Jil M. Swearingen, USDI National Park Service, Bugwood.org
AUTHORSHIP AND CITATION:
Zouhar, Kris. 2008. Berberis thunbergii. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ .
NRCS PLANT CODE :
The scientific name of Japanese barberry is Berberis thunbergii DC. (Berberidaceae) [8,24,34,36,47,73,84,89,98,111,117].
Berberis × ottawensis is a hybrid of Japanese barberry and common barberry (Berberis vulgaris) . Japanese barberry is also used to breed hybrids for horticultural purposes .
As a popular ornamental, there are numerous cultivars of Japanese barberry .
In this review, the wild type will be referred to as "Japanese
barberry", and cultivars, when identified as such in the literature, will be
referred to by cultivar name in single quotations marks (e.g., 'Sparkle').
Berberis thunbergii DC. var. atropurpurea Chenault 
FEDERAL LEGAL STATUS:
No special status
Japanese barberry is considered a pest species with varying degrees of invasiveness throughout its North American range. Information on state-level noxious weed status of plants in the United States is available through Plants Database. Invasiveness rankings are available through individual pest plant councils and land management agencies (e.g., [49,72,94,102,103,104,107,109]).
Japanese barberry is a popular ornamental and landscape plant [95,96]. Local florae indicate that Japanese barberry is commonly planted and escapes cultivation in the northeastern United States and adjacent Canada [13,36] including Ontario , Nova Scotia , Michigan , Illinois , Ohio , and West Virginia ; and the Blue Ridge Mountain counties in North Carolina [84,117], South Carolina, and Virginia . Barton and others  found that Japanese barberry spread from intentional plantings in a rural town in western Maine into surrounding deciduous forests, although it did not appear to be invasive in that area at the time of the study (2001-2002).
Japanese barberry is native to Japan . A review by Wells and Brown  states that Japanese barberry was documented in the United States by 1818. Other accounts indicate that Japanese barberry seeds were received at the Arnold Arboretum in Boston around 1875 and from there were distributed for cultivation in the United States . Japanese barberry was promoted as a substitute for common barberry, which was introduced to North America by early settlers from Europe for hedgerows, dyes, and jams, and later found to be a host for black stem rust (Puccinia graminis) of wheat and consequently eradicated . Most Japanese barberry cultivars are resistant to infection by black stem rust and are therefore approved for cultivation in the United States by the USDA, Agricultural Research Service. Fewer cultivars are approved by Agriculture Canada for cultivation in Canada. However, Japanese barberry is considered invasive in many areas (see Other Status), although some cultivars may be less invasive than others (see Regeneration Processes).HABITAT TYPES AND PLANT COMMUNITIES:
In southern Maine, dense populations of Japanese barberry occurred at 2 coastal forest sites. On Monhegan Island, Japanese barberry occurred where the upper stratum of the overstory was dominated by American mountain-ash (Sorbus americana), white spruce (Picea glauca), and balsam fir (Abies balsamea), and the lower stratum was dominated by chokecherry (Prunus virginiana). At the Wells National Estuarine Research Reserve, Japanese barberry occurred on a site dominated by gray birch (Betula populifolia) in the upper strata and chokecherry in the lower stratum. Native species regenerated poorly and were sparse under the Japanese barberry canopy . Japanese barberry also occurred in eastern white pine (Pinus strobus) forests on old fields, and in mixed hardwoods on the Rachel Carson National Wildlife Refuge in Maine .
The Bartlett Experimental Forest in eastern New Hampshire was surveyed in the late 1960s, and Japanese barberry was present but confined mostly to a red maple (Acer rubrum) swamp . In a chronosequence study of old field successional communities in southeastern New Hampshire that included at all stages of succession ranging from 14 to over 200 years since abandonment of agricultural use, Japanese barberry occurred in all community types except the gray dogwood (Cornus racemosa) type. It occurred in the early successional common juniper-Allegheny blackberry-sweetfern (Juniperus communis-Rubus allegheniensis-Comptonia peregrina) community type (estimated at 17±5 years after abandonment); the eastern white pine community type (estimated at 81±46 years after abandonment); the northern red oak-mapleleaf viburnum (Quercus rubra-Viburnum acerifolium) community type (estimated at 97±59 years after abandonment); and the eastern hemlock (Tsuga canadensis) community type (estimated at 134±61 years after abandonment), with American beech (Fagus grandifolia), eastern white pine, northern red oak, and sweet birch (Betula lenta) as common components .
In the Berkshire region of western Massachusetts, Japanese barberry dominated and in some cases had more than 80% cover in the understory of a mature, closed-canopy, deciduous forest dominated by sugar maple (Acer saccharum), sweet birch, and white ash (Fraxinus americana). Japanese barberry, multiflora rose (Rosa multiflora), gray dogwood, silky dogwood (Cornus amomum), and winterberry (Ilex verticillata) were common components of a closed-canopy, forested swamp dominated by white ash and red maple with a dense shrub understory dominated by nonnative Morrow’s honeysuckle (Lonicera morrowii) [86,88]. At Quabbin Reservoir Reservation in central Massachusetts, Japanese barberry occurred in widely scattered populations; extensive and fairly uniform populations occurred under a canopy dominated by white ash. Associated overstory species included eastern white pine, red pine (P. resinosa), black cherry (Prunus serotina), and sugar maple [11,12]. A survey of 159 forested sites at the Reservation found that Japanese barberry rarely occurred in eastern hemlock and spruce (Picea spp.) stands . Inventory and vegetation classification of floodplain forest communities in Massachusetts found that nonnative Japanese barberry, multiflora rose, and Oriental bittersweet (Celastrus orbiculatus) occurred and had high indicator values in highly disturbed floodplain forests along major rivers. Dominant vegetation in these communities included silver maple (Acer saccharinum), eastern cottonwood (Populus deltoides), boxelder (Acer negundo), and ostrich fern (Matteuccia struthiopteris) . Japanese barberry was one of the most frequent invasives observed in the Quinnebaug Highlands forest of southern Massachusetts and northern Connecticut. This study site was located in the transition zone between the central hardwood forest dominated by various oaks (Quercus spp.), hickories (Carya spp.), red maple, and sweet birch, and the northern hardwood forest dominated by sugar maple, American beech, eastern hemlock, and eastern white pine .
Japanese barberry was planted in Platt Park near Southbury, Connecticut, around 1960 to 1965. A floristic inventory and vegetation classification conducted in 1995 describes a sugar maple-Japanese barberry-northern spicebush (Lindera benzoin) cover type where sweet birch and northern red oak were common associates. Japanese barberry had 9% cover and 75% frequency, and northern spicebush had 8% cover and 100% frequency in the shrub stratum. The dominant herbaceous species in this cover type was the evergreen Christmas fern (Polystichum acrostichoides). On the lower southeastern slope of the cover type, pure thickets of Japanese barberry persisted. The cultivated shrubland-woodland cover type consisted of a strip of vegetation running parallel to an abandoned farm road. The majority of vegetation in this cover type consisted of planted and nonnative species and was characterized by dense shrubs and many weedy forbs, sedges, and grasses. Common tree species included small individuals of eastern hemlock, eastern redcedar (Juniperus virginiana), eastern white pine, and European crab apple (Malus sylvestris). Japanese barberry occurred in the shrub stratum in dense thickets along with common barberry, autumn-olive (Elaeagnus umbellata), multiflora rose, smooth sumac (Rhus glabra), Bell's honeysuckle (Lonicera × bella), and European privet (Ligustrum vulgare). Two species of poison-ivy (Toxicodendron radicans and T. rydbergii) carpeted the ground and climbed shrubs and trees. Japanese barberry also occurred in a few patches in the understory of the eastern hemlock cover type in the park .
In the Black Rock Forest in southeastern New York, Japanese barberry formed a large area of continuous canopy in the understory of a second-growth forest dominated by northern red oak, chestnut oak (Q. prinus), and red maple. Co-occurring native shrubs included black huckleberry (Gaylussacia baccata), mountain-laurel (Kalmia latifolia), pink azalea (Rhododendron periclymenoides), highbush blueberry (Vaccinium corymbosum), and other blueberries (Vaccinium spp.) . Ostfeld and others  described a habitat in rural southeastern New York with 60- to 80-year-old stands of sugar maple that developed following abandonment of cultivated fields; the sparse understory vegetation was dominated by Japanese barberry. On forests dominated by sugar maple and American beech that had been selectively logged but never cleared for cultivation, Japanese barberry occurred at <1% relative cover on 23% of sites surveyed in 1999. It did not occur in these forests in 1938 . Japanese barberry occurred at 0.8% relative cover in oak-hickory (Carya spp.) forests at the Cary Arboretum, Hudson Valley, New York, but did not occur in chestnut oak or red maple forests when surveyed in 1984 . On Robins Island, Japanese barberry is most common in red maple swamp and common reed (Phragmites australis) marsh plant communities. Associated species in red maple swamp communities include black cherry, black tupelo (Nyssa sylvatica), common greenbrier (Smilax rotundifolia), multiflora rose, grape (Vitis spp.), grasses (Panicum and Agrostis spp.) and rushes (Juncus spp.). Common reed marshes support a variety of herbaceous species .
Informal survey results suggest that Japanese barberry is common in the understory of closed-canopy deciduous forests throughout central and northern New Jersey and adjacent areas of Pennsylvania and New York . Japanese barberry populations in Morristown National Historic Park, New Jersey, occurred under a closed canopy of mature hardwood trees including yellow-poplar (Liriodendron tulipifera), white oak (Q. alba), black oak (Q. velutina), northern red oak, red maple, sugar maple, sweet birch, and white ash . The typical native understory in these forests is characterized by blueberries (Vaccinium spp.) and huckleberries (Gaylussaccia spp.) . Kourtev and others  compared characteristics of soils and vegetation in invaded and uninvaded sites in 3 parks in northern New Jersey. The canopy in all sites was composed of a mixture of oaks, American beech, yellow-poplar, sweet birch, white ash, red maple, sugar maple, and other species. Invaded areas had fewer oaks and more yellow-poplar and white ash in the canopy, and the native understory shrubs deerberry (Vaccinium stamineum) and hillside blueberry (V. pallidum) were significantly less abundant (P<0.05). On one site, heavy deer browsing had eliminated most shrubs other than Japanese barberry. Several other nonnative shrubs and vines occurred in invaded areas. Japanese barberry often occurred with Japanese stiltgrass (Microstegium vimineum), the latter carpeting the ground between Japanese barberry shrubs. The authors noted that neither Japanese barberry nor Japanese stiltgrass was widespread 10 years prior to their study, with surveys in Morristown National Historic Park reporting no Japanese stiltgrass and only a few isolated individuals of Japanese barberry . Japanese barberry was a relatively common component of some upland forest stands in northern New Jersey that had been free of major disturbance for at least 60 years. For details of the shrub and herbaceous components of the 55 forest stands studied, see Davidson and Buell .
Japanese barberry occurs on a floodplain site dominated by sliver maple, boxelder, green ash (Fraxinus pennsylvanica), sycamore (Platanus occidentalis), and slippery elm (Ulmus rubra) within an oak forest in Maryland .
Japanese barberry cover was "minor" in a northern red oak-mixed hardwood forest in Pennsylvania surveyed in midsummer 2002. However, the authors suggested that Japanese barberry, Japanese stiltgrass, and ferns (Polypodiophyta) "may inhibit forest regeneration" .
In an old-growth oak-sugar maple-hickory forest in southwestern Ohio, Japanese barberry had a relative frequency of 1.3% and relative density of 0.3%. It did not appear on the hillsides in the surrounding area . In a second-growth (>100-year-old), mixed-deciduous forest dominated by sugar maple and white ash in southwestern Ohio, Japanese barberry had 6.7% frequency, <0.01 m²/ha basal area, and density of 28 individuals/ha. Associated shrubs included blackhaw (Viburnum prunifolium), northern spicebush, and the nonnative Amur honeysuckle (Lonicera maackii) .
Japanese barberry occurred at low density (<20 stems/ha) in lowland forest stands in southeastern Wisconsin. Stands were dominated by silver maple, with black ash (Fraxinus nigra) and green ash as subdominants. Yellow birch (Betula alleghaniensis), red maple, American elm (Ulmus americana), boxelder, and hawthorn (Crataegeus spp.) were the next most common tree species. The shrub layer was dominated by currant (Ribes spp.), sumac (Rubus spp.), and gray dogwood. Stands were variably affected by Dutch elm disease and consequently had variable amounts of American elm mortality, ranging from 0 to 28 dead trees per hectare across 15 stands. Species composition of stands was not significantly related to the number of dead canopy elms .
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
Aboveground description: Japanese barberry is a deciduous shrub, usually about 3 to 6 feet (1-2 m) tall but ranging from about 1 to 10 feet (0.3-3 m) tall [34,36,45,84,98,100]. Shrubs have multiple stems  originating from the root crown, plus shoots arising from rhizomes at variable distances from the root crown . Individual shrubs are typically dense and compact [36,84,93,100] and usually broader than tall at maturity, with widths of 3 to 8 feet (1-2.5 m) . Stems may be erect to decumbent , and have short axillary shoots  and dense, spreading branches . Ehrenfeld  also refers to shoots arising from stolons. Aerial stems have simple, short, stiff spines [34,36,45,73,84,93,98] and dense foliage . Leaves are simple and entire [34,36,73,84], typically about 0.2 to 1 inch (0.5-2.5 cm) long and 3 to 18 mm wide [34,84,100], with short petioles, 0 to 8 mm [34,36]. Flowers are 8 to 15 mm wide [34,36,84] and solitary or borne in small, umbellate clusters of 2 to 5 flowers [34,36,73,84,98,100,111] along the entire length of the stem . Fruits are bright red berries [34,84,100] with dry flesh [13,73], about 7 to 11 mm long [34,36,84,100].
Cultivars of Japanese barberry vary mainly in foliage color, growth habit (size and shape), fruit production, germination, and seedling establishment [60,62].
Belowground description: Japanese barberry has a large, shallow root system with rhizomes and many fine roots radiating from a root crown . Japanese barberry populations studied on invaded sites at 3 locations in northern New Jersey produced large amounts of fine-root biomass in the surface soils, about 3 times the root biomass of native blueberries in the same areas . Sprouts occur from rhizomes at variable distances from the root base and form diffuse swarms of stems .
Plant growth form and stand structure: Japanese barberry populations range from small plants occurring at low densities to dense stands with up to 40 stems/individual, 36 stems/m² , and few plants growing under the crown area . Japanese barberry stems arise from seeds, sprout from the root crown, sprout from rhizomes, and arise from the rooting of long stems that touch the ground at variable distances from the root base. These many forms of reproduction can result in diffuse swarms of stems covering a large area, making it difficult to determine the limits of an individual genet .
The combination of multiple forms of population growth and low mortality rates allows Japanese barberry to produce dense, persistent populations. A survey of Japanese barberry populations in Morristown National Historic Park found the average number of Japanese barberry individuals ranged from 0.08 individuals/m² in a sparse population to 3.95 individuals/m² in a dense population. The average number of stems/individual ranged from 2.4 in a sparse population to 8.2 in a dense population. The average density of stems ranged from 0.53 stems/m² in a sparse population to 16.78 stems/m² in a dense population. Small, upright stems less than 20 inches (50 cm) long were most abundant in all populations regardless of density. Stems longer than 20 inches were more abundant in dense versus sparse populations . Average stem density of Japanese barberry on invaded sites at 3 other locations in northern New Jersey was 3.99, 5.01, and 3.66 stems/m². Average aboveground biomass of Japanese barberry ranged from 4 to 44 times the average aboveground biomass of the native blueberry understory . At 2 forested sites in western Massachusetts, Japanese barberry was the dominant understory species, forming thickets 6 feet (2 m) in height. At one site Japanese barberry stem density was 12 stems/m² and leaf area index (LAI) was 1.7; at another site Japanese barberry stem density was 14 stems/m² and LAI was 2.0 .
Ehrenfeld  observed on New Jersey study sites that Japanese barberry population growth accelerates rapidly, due to greater recruitment as density increases and low mortality rates. Japanese barberry seedling establishment was proportional to shoot density, so that as plants grew in size, local recruitment from seed increased. Rates of individual stem mortality were low (0.04-0.05 individuals/m²/year). Even in the densest population, survivorship of individuals was 95% to 96%. Dead stems remained standing for several months . On research plots where Japanese barberry plants were removed in southern Maine, density of Japanese barberry seedlings was not correlated with pretreatment cover of Japanese barberry. However, there was a marginally significant (P=0.055) trend of increased abundance of sprouts with increased initial Japanese barberry cover. The author speculated that the abundance of Japanese barberry sprouts on plots with high Japanese barberry cover would likely increase with additional growing seasons .RAUNKIAER  LIFE FORM:
The invasive potential of the more than 40 cultivars of Japanese barberry is not well known. Results from nursery trials designed to test the reproductive characteristics of various Japanese barberry cultivars as indicators of invasive potential suggest that some cultivars may be less invasive than others [60,62]. In particular, Lehrer and others  suggest that the smaller, less "vigorous" Japanese barberry cultivars, 'Aurea' and 'Crimson Pygmy', may be considered "safe enough" to justify their continued commercial production and sale. However, these results alone cannot be used to assess the potential contribution of individual cultivars to invasive populations, because all cultivated genotypes studied produced at least some green-leaf seedlings that resembled the invasive wild type. More research is needed to determine whether these cultivated, ornamental plants can produce the wild type . See Seed production, Germination, and Seedling establishment for details of these studies.
Pollination: Japanese barberry is pollinated by small and large bee species. Stamens respond to a tactile stimulus (e.g., a visiting bee) by snapping toward the stigma and thus depositing pollen. Small bees trip fewer stamens per visit than large bees, leaving more pollen to be subsequently removed. If visits are frequent, small bees could be more effective pollen dispersers, and if visits are rare, large bees may be more effective dispersers because they remove more pollen per visit and leave a smaller proportion of pollen undispensed .
Seed production: Seed production rates are not well studied for Japanese barberry under field conditions. Observations of Japanese barberry seedling densities shortly after germination suggest that seed production is a function of Japanese barberry stem density (see Seedling establishment) . A study of dense, continuous stands of Japanese barberry in the University of Connecticut Forest found that Japanese barberry fruit production varied with light level, but some seeds were produced even under very low light levels (≤4% full sun) .
|Average fruit production by Japanese barberry shrubs (n=15) under variable light conditions |
Seeds per plant (SE)
Seeds/cm branch length (SE)
|89||1,500 (550)||0.141 (0.072)|
|44||1,800 (600)||0.215 (0.027)|
|4||200 (20)||0.104 (0.022)|
Cultivars: Trials of 18 cultivars or hybrids of Japanese barberry were conducted at Longwood Gardens in Pennsylvania to determine relative fruit production and germination potential. Three cultivars, 'Bogozam', 'Kobold', and 'Monlers', produced on average no more than 1 fruit per 2 inches (5 cm) of stem length. In contrast, the most prolific seed producers in the trial, 'Golden Ring', 'Rose Glow', 'Crimson Velvet', 'Sparkle', and B. 'Tara' (a hybrid of Japanese barberry and B. koreana) produced more than 3 fruits per stem inch . In a separate study, 4 forms of Japanese barberry (B. t. var. atropurpurea, 'Aurea', 'Crimson Pygmy', and 'Rose Glow') were examined to compare fruit and seed production (see table below), seed viability (see Germination), and "vigor" of the resultant seedling progeny (see Seedling establishment/growth) with those of the Japanese barberry wild type [60,61].
|Propagule production of 5 Japanese barberry forms [60,61]|
|B. t. var. atropurpurea*||2,500||3,000|
|Wild type B. thunbergii||~1,140||1,135|
|B. t. var. atropurpurea is the form from which 'Crimson Pygmy' and 'Rose Glow' were developed . It is no longer recognized as a variety .|
Seed dispersal: Most Japanese barberry fruits are dispersed by gravity, but some long-distance dispersal occurs. In New Jersey, Ehrenfeld  observed a relationship between Japanese barberry seedling density and local stem density, indicating that most berries simply drop to the ground beneath the parent plant. Similarly, of the 525 first-year seedlings mapped on Connecticut study sites, 92% were found underneath or within 3 feet (1 m) of the canopy of a Japanese barberry shrub. However, "several" were 160 feet (50 m) or more from the nearest adult, with the furthest being 260 feet (80 m) distant . An informal survey of forest preserves in the New York Metropolitan region indicated that in several instances Japanese barberry populations extend away from disturbed or open areas at least 330 feet (100 m) into undisturbed forest. Sparse populations or individual plants were noted in some areas that were not only undisturbed but separated from moderate or dense populations by several kilometers, indicating Japanese barberry spread in intact forest distant from abundant seed sources .
A review by Silander and Klepis  notes that birds are the most common animal dispersers of barberries (Berberis spp.). Birds that disperse barberries either feed directly on the fruit pulp and discard the seeds locally or ingest the entire fruit and defecate the seeds elsewhere (review by ). Several ground-dwelling birds including ruffed grouse, northern bobwhite, ring-necked pheasant, and wild turkey are listed as dispersal agents for Japanese barberry seed [95,100], and observations suggest that these and other ground-dwelling fauna may be as or more important than passerine birds for regional dispersal . Wild turkey and grouse are known to use Japanese barberry fruits heavily (Wolgast, personal communication cited in ), and recent increases in wild turkey and other frugivorous game bird populations in the northeastern United States may contribute to Japanese barberry spread [26,92].
The brightly colored fruits of Japanese barberry are available to birds throughout the winter, but they do not seem to be preferred  and are generally a low-priority food item for many birds. These birds eat them primarily late in the season (Kern 1921, as cited by ) and in critical periods when other foods are scarce or absent . Japanese barberry seed was recorded from traps, feces, and stomachs of various frugivorous birds in central New Jersey . See Importance to Wildlife for further implications of this relationship.
Seed banking: Studies in the greenhouse and on invaded sites in southern Maine  suggest that Japanese barberry does not form a large or persistent soil seed bank. Japanese barberry plants were completely removed from study plots in southwestern Maine by cutting aboveground stems in fall of 2004, and seedling densities were recorded in spring and fall of 2005. Lack of significant increase in Japanese barberry seedling density from fall 2004 to fall 2005, when shading from Japanese barberry canopy was removed, suggests that Japanese barberry did not have a substantial seed bank at these locations. A greenhouse study using litter and soil samples taken from these plots yielded the following results :
|Average density (stems/m²) of Japanese barberry seedlings emerging from litter and soil samples taken from field sites and incubated in the greenhouse |
|Fall 2004||Spring 2005||Fall 2005|
|Monhegan - litter||0||10.0||6.9|
|Monhegan - soil||4.5||16.1||9.2|
|Wells - litter||2.6||0||0|
|Wells - soil||2.6||6.3||4.7|
These results suggest that either viable Japanese barberry seed was depleted in the first year or that seed viability decreases in the second growing season after seed drop. Additional evidence of a short-lived seed bank comes from commercial Japanese barberry seed stored in the greenhouse, which had an emergence rate of 9.4% the first year and 1.8% the following year .
More research is needed to better understand seed bank dynamics in Japanese barberry.
Germination: Japanese barberry seed has a morphophysiological dormancy. Two things must happen before seeds with morphophysiological dormancy can germinate: 1) the embryo must grow to a species-specific critical size and 2) physiological dormancy of the embryo must be broken [5,6]. A period of cold stratification at about 32 to 41 °F (0-5 °C) and/or alternating temperatures from lows of about 41 to 50 °F (5-10 °C) to highs of about 68 to 90 °F (20-32 °C) seems to break dormancy of and provide optimum germination conditions for Japanese barberry seed [17,76]. Freezing does not favor afterripening and kills large numbers of imbibed seeds. Germination rates of Japanese barberry seeds reach from 60% to 70% when planted outdoors in the fall, protected from freezing, and exposed to the fluctuating temperatures of early spring .
Results of germination experiments vary somewhat with regard to the period of cold stratification and temperature regimes required for optimum germination. For example, Barton  observed no beneficial effects on germination of Japanese barberry seed from either stratification at 41 °F (5 °C) or of presoaking seeds in water. See these sources for more details: [4,17,58,76].
Cultivars: Trials of 18 cultivars or hybrids of Japanese barberry indicated that seeds from all selections were viable, with germination rates ranging from 70% to 100% . In other studies [60,61], germination rates of 4 Japanese barberry forms rarely exceed 80%.
|Average germination rates of seed from 4 ornamental Japanese barberry forms [60,61]|
Germination rate (%)
|B. t. var. atropurpurea||~72|
Lehrer  indicated that seeds collected from the wild type of Japanese barberry located in "naturalized" conditions showed high rates of predation by an unknown seed weevil and had malformations that may account for reduced viability under field conditions (data not given).
Seedling establishment/growth: Ehrenfeld  conducted a 2-year study in Japanese barberry populations in a northern New Jersey hardwood forest and found that seedling densities were highly variable among populations and years but were significantly correlated with stem densities (P< 0.0001). In 1994 Japanese barberry seedling stem densities ranged from an average (SE) of 0.17 (0.07) seedlings/m² in a sparse population to 12.90 (5.51) seedlings/m² in a dense population. In 1995, Japanese barberry seedling densities were an order of magnitude lower than the previous year and ranged from an average (SE) of 0.025 (0.025) seedlings/m² in one moderately dense population to 0.40 (0.19) seedlings/m² in another moderately dense population. Seedlings established rapidly, with relatively low rates of mortality during the first year, especially in sparse populations .
|Mortality rates (fraction of initial May 1994 cohort) for Japanese barberry seedlings in 6 populations of varying density at in Morristown National Historic Park, New Jersey |
|Population density/site number||May-August
Although seedling mortality rates can exceed 90%, the large seed set, especially in areas with high stem density, results in substantial recruitment to the population. When seedling mortality rates measured over both seasons are combined with average initial seedling densities in 1994, the recruitment rate of new individuals from seed ranges from 0.08 individual/m² in the sparse population to 0.97 individual/m² in a dense population . Studies of 2 populations in southern Maine found that most Japanese barberry seedling mortality occurred during the summer months .
Surviving Japanese barberry seedlings may persist for several years as single-stemmed plants, or additional shoots may arise from the root crown or rhizomes to form a multistemmed plant. Stems may die and arise each year, resulting in a net decrease, increase, or no net change in individual plant size each year . Ehrenfeld  observed that more plants increase in size annually than decrease. Results from field studies in Connecticut suggest a high and continuous stem turnover in Japanese barberry, with old stems dying after a few years and being replaced by new stems sprouting from the root crown. Of 43 stems assessed for radial growth, 81% were 2 or 3 years old, fewer than 7% were 4 to 6 years old, and only 1 stem was 7 years old. Thus, there is no easy way to estimate the age of individual shrubs, some of which may have persisted in the forest for several decades . Mortality of individuals is greatest for small plants with fewer than 3 stems per plant and/or stems less than 20 inches (50 cm) tall .
Japanese barberry seedling survival and and plant growth are related to light availability. Studies of 2 populations in southern Maine found a significant (P=0.003) negative relationship between forest canopy cover and density of Japanese barberry seedlings . Field studies in Connecticut indicate that radial stem growth is positively correlated with light availability (P<0.002). However, this relationship was driven by samples from intermediate and high light conditions, and considerable variation of radial stem growth was observed at light levels below 4% full sun. Japanese barberry biomass per unit area was also positively correlated with both available light and soil moisture (P=0.009). In the greenhouse, total new stem growth (length and biomass) was positively correlated with light level (P<0.001) .
A review  suggests that Japanese barberry seedlings may grow 2 to 4 feet (0.6-1.2 m) in one season, although the source of this information is not given.
Cultivars: Comparison of growth among progeny of barberry forms revealed that seedlings of the 2 larger forms, B. t. var. atropurpurea and 'Rose Glow', attained greater height and width, produced more branches, and produced heavier canopy growth than the smaller forms, 'Aurea' and 'Crimson Pygmy' [60,61]:
|Growth characteristics of seedlings derived from 4 ornamental Japanese barberry forms [60,61]|
|Form||n||Height (cm)||Width (cm)||No. branches||Dry weight (g)|
|B. t. var. atropurpurea||230||200.1a*||111.2b||5.2b||1.2b||2.5a|
Wild type Japanese barberry seedlings generally attained similar or somewhat smaller dimensions compared to B. t. var. atropurpurea and 'Rose Glow' progeny, though they had fewer branches and were "often ungainly in appearance." The strong growth of seedlings derived from some landscape cultivars may reflect inbreeding depression in the wild type, or a degree of hybrid vigor due to outcrossing of cultivars. More work is needed to understand the nature of these trends .
Vegetative regeneration: Japanese barberry spreads locally by sprouting from the root crown and rhizomes, and by layering. Recruitment from sprouting and layering is roughly an order of magnitude less than recruitment by seedling establishment . Ehrenfeld  also refers to shoots arising from stolons, but this is the only mention of stolons found in the available literature so the importance of this mode of vegetative regeneration for Japanese barberry is unclear.
Following damage or removal of aboveground stems, Japanese barberry can regenerate by sprouting from stumps , root crowns, and underground organs. At 2 study sites with dense Japanese barberry infestations in southwestern Maine, aboveground stems of Japanese barberry were completely removed by cutting at ground level in fall of 2004 and spring of 2005. Season of clipping did not have a significant effect (P>0.05) on the subsequent density of Japanese barberry or any associated vegetation .
|Density (stems/m²) of Japanese barberry sprouts on 2 sites in southern Maine treated with complete top removal of Japanese barberry |
Clipped fall 2004
Clipped spring 2005
Japanese barberry vegetative sprouts showed a tendency to decrease with increasing forest canopy cover, but the relationship had only marginal significance (P=0.058) .SITE CHARACTERISTICS:
Japanese barberry is included among those shrubs that can "tolerate adverse site conditions" such as high acidity, low fertility, and shallow soil ; and it is included in a list of shrubs recommended for strip-mine reclamation . Japanese barberry is not salt tolerant [74,75].
Silander and Klepis  suggest that the northern limits of Japanese barberry distribution are probably set by low temperature tolerances, the southern limits by cold stratification requirements (see Germination), and the western limits by drought tolerance.
Japanese barberry is less common and probably less invasive in some parts of its North American range than others. Its site affinities in some of these outlying areas are described as follows: Japanese barberry occurs occasionally in woods, swamps, fields, and dunes in Michigan ; is an infrequent escape to woodlands in the Blue Ridge Mountain counties of Virginia, North Carolina, and South Carolina ; occurs rarely on wooded slopes in scattered localities in North Carolina ; and occurs in streambank thickets in Wyoming . On 14 forested sites in central and southern Indiana, Japanese barberry did not occur more than 33 feet (10 m) from the road . In a survey of edge vegetation in 7 old-growth forests in central Indiana, Japanese barberry occurred on only 1 out of 14 edges surveyed, an edge that had a southwestern aspect .
Flora of North America  reports an elevational range of 0 to 4,270 feet (0-1,300 m) for Japanese barberry.
General climate and microclimate: Japanese barberry has a wide distribution in the eastern United States. However, it appears to be most invasive from Maryland and Pennsylvania to the north and east, as several sources (for example, [14,20,120]) describe dense thickets occurring in parts of this region. The table below provides general climatic characteristics given in this literature:
|Climatic characteristics of some locations where Japanese barberry occurs in dense stands and is considered invasive|
|Location||Average maximum temperature (°C)||Average minimum temperature (°C)||Average annual precipitation (mm)|
|Monhegan Island, Maine||22.1 in August||-7.8 in January||1,129|
|Wells Research Reserve, Maine||24.6 in July||-11.1 in January||1,219 |
|Quabbin Reservoir Reservation, Massachusetts||21 in July||-3 in January||1,140 |
|Black Rock Forest, New York||24.4 in July||-2.7 in January||1,200 |
Within these areas, Japanese barberry occurs on a variety of microsites, ranging from wetlands with saturated, organic soils to xeric ridgetops [27,52,92], but it seems to prefer mesic conditions is not as common on extremely wet or dry sites . Dense populations of Japanese barberry often occur on soils derived from glacial till [11,14,20,69] with loamy textures [20,52,54,114] that are well drained to excessively well drained [14,20,114]. In Platt Park near Southbury, Connecticut, Japanese barberry thickets persisted on the lower portion of southeastern slopes in a "rich and moist hardwood forest", with "mesic conditions" due to an abundance of seepage water, protection from desiccating winds, and "cool" air temperatures throughout the year . In a forest on the southeastern slope of the tallest hill on Monhegan Island in southern Maine, transects through Japanese barberry infestations ran through a wetland, but no Japanese barberry occurred in the wetland itself . In the University of Connecticut Forest near Storrs, Connecticut, dense, continuous populations of Japanese barberry occurred on soils varying from moderately well-drained Dystrochrepts to poorly drained Humaquepts. Soil moisture content on these sites varied from 19% to 39%. Transplant experiments in the greenhouse suggest that Japanese barberry tolerates a full range of soil moisture regimes from very poorly drained soils with soil moisture content greater than 40%; to dry ridgetops with thin soil; to coarse-textured, extremely well-drained soils with soil moisture less than 10%. However, established adults were not found on these extreme sites in the field, probably because seedlings could not establish under those conditions .
Current and past land use: Japanese barberry was introduced to North America as an ornamental and landscape plant, and some of the densest populations in forested New England landscapes occur around homesites where it was planted [11,26,65,101] and along roads [26,65]. In a study of farms in northeastern Connecticut, researchers observed very high barberry densities around orchards and house sites, although too few of these site types were sampled to allow statistical comparison to other site types . Observations in Quabbin Watershed in central Massachusetts indicate that while scattered populations of Japanese barberry occurred throughout the watershed, the propagule sources for those populations were probably the large populations found along cellar holes of old homesteads in the area . In an informal survey of forest preserves in the New York Metropolitan region, some of the populations described by respondents and observed by the author clearly originated from old hedgerows, former homesteads, or inhabited areas adjacent to the forests . In the Quinebaug Highlands of northern Connecticut and southern Massachusetts, current land development was strongly correlated with invasive plant cover and richness (P<0.001). Several nonnative invasive species were included in this study and, based on mean cover and frequency in invaded plots, the 3 most common invasives were Japanese barberry, Oriental bittersweet (Celastrus orbiculatus), and multiflora rose .
|Mean frequency and cover of Japanese barberry on plots varying in level of land development |
|n||Frequency (%)||Cover (SE) (%)|
|0 houses||118||26.3||0.74 (0.30)|
|1-2 houses||21||42.9||3.33 (1.44)|
|3-5 houses||29||48.3||0.66 (0.52)|
|6-8 houses||12||66.7||0.50 (0.42)|
|>8 houses||8||62.5||0.00 (±0.00)|
Japanese barberry also commonly occurs along roads, with populations often extending into the forest away from the road edge . In the Quinebaug Highlands, richness, cover, and frequency of all invasives studied increased with increasing road size. Richness and cover of invasive plants were significantly greater along paved roads than along trails or in unfragmented forest (P<0.0001) .
|Mean frequency and cover of Japanese barberry on plots associated with different road types, listed in order of increasing size and associated disturbance |
|n||Frequency (%)||Cover (SE) (%)|
Studies in Massachusetts  and northern Connecticut [65,101] found that past land use was a strong predictor of Japanese barberry abundance. While modern edaphic characteristics explain a substantial portion of the variation associated with Japanese barberry distribution in the Quabbin Watershed, knowledge of land-use history considerably improved understanding of Japanese barberry population densities and potential invasion mechanisms. A survey of 159 forested polygons found that distance to potential seed sources and postintroduction land use were significantly (P<0.001) better predictors of Japanese barberry abundance than preintroduction or modern land uses or soil characteristics. Recent harvesting did not influence Japanese barberry occurrence or abundance . Similarly, Townesmith  found that on old farms in northeastern Connecticut, sites that had historically been used as pastures had the highest levels of Japanese barberry, followed by formerly mowed fields and woodlots. Formerly plowed fields had the lowest barberry densities . Prevalence of contemporary and former agricultural fields in southeastern New Hampshire was the most influential feature affecting both establishment and spread of nonnatives including Japanese barberry. Japanese barberry presence was negatively correlated with road area within 0.6 mile (1 km) of occurrence and positively correlated with agricultural land within 0.6 mile of occurrence (P<0.05) .
In the Quinebaug Highlands, Japanese barberry had the highest frequency in former fields, former residential areas, and current fields (land use not specified). However, abundance of all invasive species studied was influenced more strongly by past land use than current land use. These relationships varied among individual species .
|Frequency and cover of Japanese barberry in plots adjacent to former (1934) and current (1990) forest, field, or residential land |
Cover (SE) (%)
See Successional Status for more information on the effects of land use and disturbance on Japanese barberry establishment, persistence, and dominance.
Soil characteristics and feedback loops: Japanese barberry occurrence is often associated with less acidic soils than uninvaded sites [20,52], and occurrence  and productivity [12,39] are associated with greater nitrate availability. Investigators have provided evidence that, rather than these soil characteristics contributing to site invasibility, these differences in soil characteristics between invaded and uninvaded sites likely resulted from Japanese barberry invasion and contribute to its persistence [29,51,53,54,55]. The relationship between abundance of Japanese barberry and soil characteristics has been examined by several investigators on 3 deciduous hardwood forest sites in northern New Jersey, and in the Quabbin Watershed in central Massachusetts.
Field studies on 3 deciduous hardwood forest sites in northern New Jersey [52,54] followed by greenhouse studies [29,51,53,55] found pronounced differences in soil characteristics between invaded versus uninvaded sites that seemed attributable to the presence of Japanese barberry. Invaded sites had understories dominated by Japanese barberry in the shrub layer and most invaded sites were dominated by Japanese stiltgrass in the herb layer. Understories on uninvaded sites were dominated by deerberry and hillside blueberry in the shrub layer, and native herbaceous cover was low. See Habitat Types and Plant Communities for a description of the vegetation on these sites . Soil pH was significantly higher, although more variable (ranging from 3.92 to 7.66), and litter and organic horizons were significantly thinner in invaded versus uninvaded areas (P<0.05). Japanese barberry density was negatively correlated with organic horizon thickness and oak basal area at all 3 sites; negatively correlated with litter layer thickness and native blueberry basal area at 2 sites; and positively correlated with pH at all 3 sites (P<0.05) . Total soil carbon, total soil nitrogen, and net ammonification rates were higher under native vegetation; and soil pH, available nitrate, and net potential nitrification were significantly higher (P<0.001) in soils under Japanese barberry. Nitrate reductase activities were much higher in the leaves of Japanese barberry than in leaves of most native species tested, suggesting that Japanese barberry is better able to utilize the higher nitrate supplies. Earthworm densities were also higher in the soil under Japanese barberry as compared with soils under native blueberry and huckleberry (Vaccinium spp.). Because earthworms are associated with surface litter incorporation, increased pH, and increased nitrification, the authors suggest that the worms may have helped create a soil environment that promotes the growth of Japanese barberry more than native shrubs .
Because the land use history is not different between invaded and uninvaded sites, the researchers hypothesized that differences in soil characteristics may be caused by the Japanese barberry invasion itself, rather than having occurred prior to invasion . Further research demonstrated that differences in soil pH, nitrification rates, and net nitrogen mineralization rates could be replicated in the greenhouse by growing Japanese barberry in previously uninvaded soil, indicating that these differences result from the presence of Japanese barberry plants . Additional studies provided evidence that these changes in soil characteristics occurred via changes in the composition and activity of the soil microbiota [51,53,55]. These results demonstrate that Japanese barberry presence can rapidly alter the soil microbiota and associated soil characteristics (nitrogen availability and pH) and processes (nitrogen mineralization) on invaded sites .
Changes in soils that alter growth of invasives may be an important component of site invasibility . Japanese barberry produces a large amount of leaf, stem, and fine-root biomass, all of which have higher nitrogen concentrations than the native tree and shrub species in the northern New Jersey studies. Consequently, Japanese barberry litter is higher in nitrogen and decomposes more rapidly than litter of the native species, with little or no net immobilization of nitrogen. High concentrations of nitrate reductase in Japanese barberry leaves imply high rates of nitrate uptake, which is supported by both pot and field studies . Studies in the Quabbin Watershed suggest that nitrogen availability was the primary limitation to Japanese barberry dominance on study sites. Nitrogen availability limited barberry growth and productivity but soil acidity or rock-derived nutrients (calcium, phosphorus, potassium, and manganese) did not. Relative growth rate and foliar nitrogen concentration of barberry were correlated with rates of nitrogen mineralization and nitrification (P<0.05), but not correlated with soil pH . Harrington and others  found that higher nitrogen availability led to higher foliar nitrogen content, increased photosynthesis at light saturation, and greater specific leaf area in Japanese barberry, suggesting that increased allocation to leaves and increased foliar nitrogen both contributed to increased production.
Japanese barberry may thus promote a positive feedback loop in which the species increases the rate of net nitrification and and available nitrate, which it preferentially takes up to support its large biomass. Increases in the size and density of shrubs  then augment the input of rapidly degradable leaf litter to the forest floor and large amounts of nitrogen-rich fine root litter to the soil. This promotes increased nitrification, resulting in greater nitrate availability, which favors Japanese barberry over native shrubs .
Japanese barberry is shade tolerant and may establish and persist in any successional stage. Examples from the available literature suggest that it probably establishes best on open, disturbed forest sites in early succession and usually persists as forest succession proceeds. However, some accounts indicate that Japanese barberry does not always persist or persists only in open areas in some communities as succession proceeds. Substantial evidence indicates that Japanese barberry establishment is not restricted to open sites, and that establishment and persistence in late-successional environments is common.
Japanese barberry is a widely planted ornamental that has spread not only into open fields and forest edges adjacent to human development, but also into closed-canopy forest. On a variety of old fields in southeastern New Hampshire, Japanese barberry occurred at all stages of forest succession ranging from 14 to over 200 years (see Habitat Types and Plant Communities) . In a study of Massachusetts hardwood forests dominated by sugar maple, Japanese barberry occurred at 11% frequency on "primary" forests, 19% frequency on "19th-century secondary" forests, and 45% frequency on "20th-century secondary" forests. Forests classified as primary were those forested in both 1830 and 1942, and secondary forests were those cleared for agricultural use in the past. Nineteenth-century secondary forests were open in 1830 and forested in 1942; and 20th-century secondary forests were either open or in early successional vegetation in 1942 . Informal surveys suggest that Japanese barberry is a common component in the understory of closed-canopy forests in the New York metropolitan area and possibly throughout the northeastern United States .
Dense Japanese barberry stands may have few understory plants growing under the crown area . On study plots at 2 sites in southern Maine, a large number of plots had 100% Japanese barberry canopy cover and low frequency of other plants. Native species regenerated poorly under Japanese barberry, although native stem densities were not correlated with percent cover of Japanese barberry. Frequency of native herb, shrub, and tree seedlings was too low to be analyzed at one site, where an average of 50% of plots lacked seedlings. Seedlings of Japanese barberry were more abundant than any other plant life form at this study site, with more than twice the maximum density (162.4 Japanese barberry stems/m²) of understory herbs (80.9 herb stems/m²). When Japanese barberry plants were removed by clipping, plots clipped in spring had higher density of herbs than those clipped in fall. This is probably because herbs were released in early spring and could respond to the increased light. Species found in fall 2004 typically had increased density in fall 2005. Tree seedling densities were consistently low, with little short-term recovery after Japanese barberry removal .
Shade tolerance: Japanese barberry tolerates full sun, part sun, and shade, and may occur under almost any shade level. In the University of Connecticut Forest, dense populations of Japanese barberry occur under light conditions from 4% to 89% of full sunlight . On a variety of old field sites in southeastern New Hampshire, Japanese barberry occurred at all successional stages studied, where photosynthetically active radiation at 16 inches (40 cm) above ground averaged 5.0%, with a minimum of 0.8% and a maximum of 17.0% . Japanese barberry populations in an "advanced stage of invasion" at 2 sites in southern Maine occurred where forest canopy cover ranged from 60% to 90%. Many plots had 100% Japanese barberry canopy cover and low frequency of other plants. Low densities of Japanese barberry seedlings and understory herbs were associated with high forest canopy cover .
A landscape-level survey in the Quabbin Watershed, where Japanese barberry occurs in the understory of forests dominated by white ash, revealed that Japanese barberry LAI (used as an indicator of vigor) was inversely correlated with overstory LAI but was not correlated with any other site variable. This suggests that Japanese barberry can persist in shaded understory conditions and increase in vigor as overstory canopy LAI decreases . Japanese barberry fruit production varies with light level, but can occur even under very low light levels (≤4% full sun) (see Seed production). Biomass per unit area (P=0.009) and radial stem growth (P<0.002) were positively correlated with light availability at the University of Connecticut Forest. Transplant experiments showed Japanese barberry survival at light levels of <1% to 90% transmittance; however, in greenhouse experiments about 60% mortality occurred at light levels <1% transmittance, with "very few" deaths at intermediate or high light levels. Under full sun, Japanese barberry occurs with other fast-growing woody species such as multiflora rose, eastern poison-oak (Toxicodendron toxicarium), blackberry (Rubus spp.), Oriental bittersweet, and various tree seedlings and saplings. However, it does not dominate these sites .
Establishment and persistence in early succession: Successional patterns on the New England landscape in the last century influence present-day Japanese barberry occurrence, distribution, and local abundance. Modern forests and natural areas have a complex disturbance history influenced by human settlement and development. Japanese barberry was introduced at a time when much of the landscape had been cleared of forest and was under cultivation or used as pasture for domestic livestock. Shortly after this time, in the early 20th century, much of this agricultural land was abandoned. The period of historical agricultural abandonment in New England represents a major pulse in resource availability (sensu ) that resulted in dramatic, persistent changes in the distribution and abundance of native and nonnnative species. The densest populations of Japanese barberry apparently resulted from a combination of open site conditions in the early 20th century, propagule availability, and site fertility .
The strong relationship between modern abundance of Japanese barberry and historical agriculture suggests that Japanese barberry established in open fields and persisted as sites succeeded to forest. In the Quabbin Watershed, Japanese barberry was most likely to occur on sites that remained as arable or pasture land after its introduction and less likely to occur on sites that were continuously wooded or reforested prior to Japanese barberry introduction . On farms in northeastern Connecticut, stone walls form boundaries between old fields, probably indicating differences in past use; some of these walls divide areas of high Japanese barberry d ensity from areas where it is scattered. Other than house and orchard sites (which were too few to be included in the analysis), historically pastured fields had the highest levels of Japanese barberry, followed by fields that were historically mowed or used as woodlots. Historically plowed fields had the lowest barberry densities. Higher densities in former pastures may be due to the type of physical disturbance (compared with mowing and plowing) or to changes in soil properties from disturbance and fertilization from livestock. None of the sites included in this study were described as "undisturbed" .
The presence of Japanese barberry in second-growth forests may be evidence of prior grazing. Japanese barberry is apparently rarely browsed by livestock and, according to anecdotal accounts, is common in actively grazed pasture land, although generally at lower densities than in forests. Therefore, if it establishes on active pasture land it will likely persist, and once grazing ceases it may be an important component of the early-successional flora . Similarly, Japanese barberry persistence and spread in forests may be facilitated by its unpalatability to wildlife. While one review  classifies Japanese barberry as a plant "highly preferred by mule deer", several other reviews and accounts suggest that it is not palatable to white-tailed deer [11,26,95,115] (see Importance to Wildlife and Livestock). It is further suggested that high densities of deer may contribute to the spread of Japanese barberry because deer dislike it and browse on natives, giving Japanese barberry an advantage [95,115]. On one site in northern New Jersey, researchers observed that heavy white-tailed deer browsing eliminated most other shrubs . A study in deciduous forest in Rondeau Provincial Park, Ontario, found that Japanese barberry occurrence was characteristic of plots grazed by white-tailed deer .
Several examples from the literature indicate that Japanese barberry does not always persist after establishment in early succession, or that it persists only on sites that remain open in these communities. An old field in southeastern Connecticut was cultivated until about 1945, grazed until 1951, burned in spring 1954, and surveyed later in 1954 for frequency and cover of plant species. Japanese barberry was present (at <1% cover and <3 feet (1 m) tall) only in the first survey year and was not detected on subsequent sampling dates (1960, 1973, 1983, and 1992), as vegetation changed from an open, herbaceous, perennial meadow to a thicket of woody vegetation . A permanent plot study indicates that Japanese barberry was absent prior to a hurricane in Massachusetts in 1938 that resulted in complete loss of the canopy in a mixed hardwood-eastern white pine-eastern hemlock forest. Japanese barberry established sometime during the 2 years following salvage logging and slash pile burning after the hurricane and stayed at 8% frequency from 1940 through 1991, showing an affinity for open, herbaceous habitats . In coastal southern New England and adjacent New York, Japanese barberry occurred in open habitats (and not in forest, shrubland, or heath habitats) and averaged 3.1% frequency and 0.5% cover . Observations in Black Rock Forest in Cornwall, New York, suggest that Japanese barberry is common on disturbed sites including roadsides and recently cut areas. It also "still grows on sites cut thirty years ago, but is being gradually replaced...in open sites" by highbush blueberry (Vaccinium corymbosum) . Stem density of Japanese barberry was higher in young and midsuccessional forests than in mature forests on 14 forested sites in the transitional zone between western mesophytic forest and beech-maple (Fagus-Acer spp.) forest in central and southern Indiana .
Establishment following modern (late 20th century) disturbances: At a landscape scale, Japanese barberry occurrence or abundance does not appear to be influenced by disturbances such as harvesting activity occurring since 1984 in the Quabbin Watershed, Massachusetts . However, several smaller-scale studies indicate a potential for early-successional establishment of Japanese barberry following disturbance of the forest canopy. In a 9-year study to assess forest response to hemlock woolly adelgid infestation on 2 eastern hemlock stands, there was no evidence of either hemlock woolly adelgid infestation or nonnative plants in 1994. In 2003, 25% of monitored eastern hemlock trees were either dead or in severe decline, and nonnative plants including Japanese barberry, tree-of-heaven (Ailanthus altissima), garlic mustard (Alliaria petiolata), Japanese stiltgrass, and multiflora rose occurred in 35% of established permanent vegetation plots. Nonnative plant occurrence was not significantly related to light availability, and suggests that propagule pressure may be more limiting than light in early stages of nonnative plant invasion . Similarly, nonnative invasive species such as Japanese barberry, Oriental bittersweet, tree-of-heaven, and Japanese stiltgrass occurred in "several" eastern hemlock stands damaged by hemlock woolly adelgid infestation in south-central Connecticut . Japanese barberry was among the most frequently encountered nonnative invasive species on 44 early-successional sites surveyed in southeastern New Hampshire in 2004 . Japanese barberry and several other nonnative plants established either from the seed bank or from outside sources after researchers removed Norway maple (Acer platanoides) by cutting trees and removing seedlings [112,113].
Establishment or persistence in late-successional environments: Japanese barberry infestations have been reported in areas distant from marked trails and distant from areas of obvious current or former disturbance . The current distribution of Japanese barberry reflects, to some degree, its ability to establish and persist in forests, which is largely influenced by proximity to seed sources. In the Quabbin Watershed, Japanese barberry occurs in nearly 36% of sites that were wooded in the early 20th century, suggesting that Japanese barberry can establish in a forested landscape even in the absence of agricultural disturbances . The historical distribution of Japanese barberry as reflected in herbarium records suggest that there has been a slow increase in the frequency with which it has been observed in closed-canopy forest :
|Habitats in which Japanese barberry has been observed during the last century as reflected in herbarium records |
|Date of collection||Total number of observations||Percentage of observations|
|Disturbed forest or cultivated field||Undisturbed forest|
Japanese barberry was present but not common in stands that were 90 years old or >200 years old in a chronosequence study of succession from old field to deciduous forest in southwestern Ohio. Japanese barberry did not occur in 2-, 10-, or 50-year-old stands . In a mature mixed-oak forest in New Jersey that had never been cut, Japanese barberry occurred with trace cover in the herb layer on 1 plot (1% frequency) in 1950 but did not occur in any plots in the herb layer in 1969 or 1979. It did not occur in the shrub layer in any plots in 1950 or 1969, but occurred with trace cover on 1 plot in 1979 . Japanese barberry was a relatively common component of some upland forest stands in northern New Jersey that had been free of major disturbance for at least 60 years .
Japanese barberry seeds germinate in May in New Jersey , presumably when temperature regimes are appropriate for germination (see Germination). Leaves on established plants emerge in late March in northern New Jersey  and on the Black Rock Forest in southeastern New York [118,120]. Japanese barberry is one of the first woody plants to leaf out in the spring, perhaps a month or more before the tree canopy is fully leafed out; it retains its leaves after most of the canopy leaves have dropped in the fall. This longer growing season likely gives Japanese barberry an advantage over native shrubs and herbs  (see Phenological niche separation). Japanese barberry flowers from late winter (March) through spring . Beginning in October 1998, Japanese barberry fruits were dispersed rapidly from shrubs in low light conditions on study sites in Connecticut, with about 30% remaining by November. By January 1999, most fruit was dispersed from shrubs across all light levels .
|Flowering and fruiting dates for Japanese barberry in different areas|
|Area||Flowering date||Fruiting dates|
|Carolinas||March to April||May to September |
|Illinois||April to May ||...*|
|West Virginia||April to May ||...|
|Blue Ridge counties in North Carolina, South Carolina, and Virginia||March to April ||...|
|New England||May 15 to June 9 ||...|
|Northeast||mid-April to May [92,100]||fruits mature from July to October and either persist  or are dispersed through fall and winter |
|Southeast||March to April||fruit matures May to September and is often present through winter |
Phenological niche separation: Phenology of Japanese barberry differs from that of native species in invaded communities in several ways. For example, the timing and magnitude of nutrient uptake and litter deposition differ between Japanese barberry and associated native plants, which alters carbon and nutrient fluxes and pools in and on the soil in invaded communities  (see Feedback loops). Japanese barberry leafs out earlier than associated species in closed-canopy deciduous forests, which may give it an advantage by providing a substantial spring carbon subsidy when high light is available (review by ). Leaf phenology, photosynthesis, and respiration of Japanese barberry and 2 co-occurring native shrubs, the evergreen mountain-laurel and the deciduous highbush blueberry, were compared at the Black Rock Forest in southeastern New York in 2004. Japanese barberry leafed-out about 1 month earlier than highbush blueberry and about 2 to 3 weeks prior to overstory trees. The overstory canopy closed by mid-May, and Japanese barberry leaf development was complete in June [118,120].
A temporal photosynthetic niche separation was observed among Japanese barberry, mountain-laurel, and highbush blueberry. The photosynthetic capacity of Japanese barberry was highest under the open canopy in spring and declined with canopy closure. Overwintering leaves of mountain-laurel had high photosynthetic capacity in the spring, while photosynthetic capacity of new spring leaves gradually increased to a peak in mid-September. Highbush blueberry had low photosynthetic capacity throughout the growing season . Japanese barberry showed the lowest stomatal limitation to photosynthesis among the 3 shrubs [118,120]. Japanese barberry acclimated to varying irradiance through active nitrogen allocation and modification of leaf morphology, and showed dynamic adjustments in the amount of leaf nitrogen invested in the photosynthetic apparatus that was not seen in the native shrubs. Japanese barberry had high leaf nitrogen in early May that decreased 50% by mid-June and remained low throughout the rest of the growing season [118,120]. Japanese barberry also down-regulated respiration following canopy closure. Japanese barberry respiration rate was highest in early May, lowest in mid June, and then gradually increased during the growing season .
These phenological characteristics are likely to favor Japanese barberry by providing both a spring carbon subsidy and reducing maintenance cost following canopy closure . Additionally, Japanese barberry has total annual leaf respiration similar to those of mountain-laurel and highbush blueberry, and seems to have a higher ratio of photosynthesis to respiration (i.e., carbon gain) than these native shrubs . More information is needed to fully understand these relationships and their implications to site invasibility under current conditions and under conditions of climate change (see Other Management Considerations).
Underground phenology: Woody species utilize stored, belowground carbohydrate reserves to survive dormancy and disturbance. These reserves naturally fluctuate over the course of a year: declining in the spring during leaf flush and shoot elongation and increasing during the growing season when excess photosynthate is produced (review by ). Although it is difficult to interpret results and draw conclusions due to small sample sizes and lack of replication, some interesting trends were observed in total nonstructural carbohydrate (TNC) levels in Japanese barberry as compared with other nonnative shrubs studied by Richburg . TNC levels in all species were depleted in early spring; however, whereas most species required most of the growing season (4 to 5.5 months) to replenish TNC reserves, Japanese barberry TNC levels recovered within 31 to 35 days. A second and unexpected decline in TNC reserves was observed in Japanese barberry during the growing season (July to September 2001), after which reserves were replenished in October. The author speculates that this pattern was related to precipitation, as depletion of TNC coincided with 35% to 52% below-average rainfall in July and August, and replenishment of TNC followed above-average rainfall in September. Depletion of TNC was not observed in Japanese barberry during a year with average precipitation throughout the growing season (2002). Japanese barberry TNC levels did not decrease during flowering and fruiting .
Japanese barberry can probably establish after fire from off-site seed sources and possibly from the soil seed bank as suggested in a review by Huebner , although limited seed banking information suggests that substantial seed banking is lacking for this species. More information is needed on seed banking and heat tolerance of Japanese barberry seed.
Fire regimes: While it is unclear what type of fire regime Japanese barberry is best adapted to, it most commonly occurs in northern hardwood forests (see Habitat Types and Plant Communities) that experience long fire-return intervals (see Fire Regime table, below), and it has been suggested that repeated fires decrease Japanese barberry abundance . Wind and insects are more common disturbance agents than fire in northern hardwood forests, and fire-return intervals in these forests have been estimated at several hundred to several thousand years (e.g., ). Japanese barberry may also occur on sites with potential natural vegetation that is adapted to more frequent fire, such as oak-hickory communities. However, at 3 sites in New Jersey, oak basal area was significantly lower (P<0.05) on Japanese barberry invaded versus uninvaded areas; and yellow-poplar and white ash basal area tended to be greater in invaded areas .
Plant communities in the northeastern United States have been severely altered by human settlement during the past several centuries, and the potential natural vegetation may be difficult to discern on many sites. Fire regimes have also been altered by European settlement. In some cases, such as in northern hardwood forests, fire occurrence may have increased; but overall, with fire exclusion policies beginning around the 1920s, fire occurrence decreased throughout the eastern United States. As a result, many oak-hickory and other communities previously maintained by fire have converted to closed-canopy forests; and shade-tolerant, fire-sensitive plants have begun to replace sun-loving, fire-tolerant plants. Thus a cool, damp, shaded microenvironment with less flammable fuel beds develops and favors shade-tolerant mesophytic species over shade-intolerant, fire-adapted species . More moist, shady conditions may favor the persistence and spread of Japanese barberry in some areas (see Site Characteristics).
Fuels: According to a review by Richburg and others , fuels from woody invasive species in the northeastern United States can be categorized into 2 types: 1) those that increase a fire hazard and 2) those that do not increase the fire hazard of an area. While Japanese barberry may increase biomass in the shrub layer on invaded sites [21,29] and may be more flammable than associated native species , unsuccessful attempts to use prescribed fire in invaded stands during the growing season suggest that Japanese barberry probably does not increase the fire hazard in invaded communities during the growing season .
Shrub cover, height, and frequency were higher in invaded versus uninvaded forests where Japanese barberry occurred in New Jersey and Maine. In a mixed-deciduous forest in New Jersey, the average aboveground biomass of Japanese barberry ranged from 4 to 44 times the average aboveground biomass of the native blueberry understory . In eastern white pine forests on old fields and in mixed hardwoods on the Rachel Carson National Wildlife Refuge in Maine, Japanese barberry was in some areas "a wall of thorny vegetation" that might present "a substantial live fuel that is significantly more abundant than the shrub layer in a nearby uninvaded stand". The authors suggest that this could either increase or decrease fire frequency and intensity, and that fire behavior may vary according to the heat content of the invasive species . Based on this hypothesis, combustion characteristics of foliage and twigs of several eastern native and nonnative species were measured in a cone calorimeter. The average heat of combustion (15.63 MJ/kg) and total heat release (14.55 MJ/kg) for Japanese barberry were higher than those of most other species tested. However, a comparison of invasive plants, including Japanese barberry, and co-occurring noninvasive plants, found that the average heat of combustion was significantly (P<0.0001) higher for the noninvasive species as a group. Average time to sustained ignition and peak heat release rate were also presented. See Dibble and others  for details.
Japanese barberry generally invades areas that rarely burn and does not seem to increase the threat of fire . Sites invaded by Japanese barberry may have less surface fuel, as Japanese barberry density was negatively correlated (P<0.05) with litter layer and organic horizon thickness on invaded sites in New Jersey  (see Soil characteristics). Treatments to control Japanese barberry, such as cutting, can increase the fuel load, but probably not enough to present a hazard during the growing season (see Fire Management Considerations). Researchers were unable to ignite Japanese barberry slash during the growing season in treated stands in mature deciduous forest sites dominated by sugar maple, black birch, and white ash. However, dormant-season burning was accomplished in November and April in treated and untreated Japanese barberry stands, respectively .
The following table provides fire regime information on vegetation communities in which Japanese barberry is most likely to be a common or dominant component, based on descriptions in available literature. The table does not include plant communities across the entire distributional range of Japanese barberry. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".
|Fire regime information that may be relevant to Japanese barberry. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models . These vegetation models were developed by local experts using available literature, local data, and/or expert opinion as documented in the PDF file linked from the name of each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Northern hardwood maple-beech-eastern hemlock||Replacement||60%||>1,000|
|Northern hardwood-eastern hemlock forest (Great Lakes)||Replacement||99%||>1,000|
|Surface or low||76%||11||2||25|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Northern hardwoods (Northeast)||Replacement||39%||>1,000|
|Eastern white pine-northern hardwoods||Replacement||72%||475|
|Surface or low||28%||>1,000|
|Northern hardwoods-eastern hemlock||Replacement||50%||>1,000|
|Surface or low||50%||>1,000|
|Appalachian oak forest (dry-mesic)||Replacement||2%||625||500||>1,000|
|Surface or low||92%||15||7||26|
|Northeast spruce-fir forest||Replacement||100%||265||150||300|
|Vegetation Community (Potential Natural Vegetation Group)||Fire severity*||Fire regime characteristics|
|Percent of fires||Mean interval
|Mixed mesophytic hardwood||Replacement||11%||665|
|Surface or low||79%||90|
|Eastern hemlock-eastern white pine-hardwood||Replacement||17%||>1,000||500||>1,000|
|Surface or low||83%||210||100||>1,000|
Replacement=Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed=Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low=Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [38,56].
Japanese barberry can probably establish after fire from off-site seed sources and possibly from the soil seed bank as suggested by Huebner , although seed banking information is limited and suggests that substantial seed banking is lacking for this species. One study reports establishment of Japanese barberry 4 years after a prescribed fire in a mature stand of red pine (Pinus resinosa) and eastern white pine (Pinus strobus) in Michigan. Japanese barberry seedlings were absent from all plots subject to biennial burning (1991, 1993, and 1995) when sampled in 1994 and 1995, and were absent from once-burned (in 1991) and unburned control plots in 1994. In 1995, Japanese barberry occurred at 0.9% relative frequency and 0.33% cover on once-burned plots and at 0.4% relative frequency and 0.03% cover on unburned control plots .
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Phenology of Japanese barberry at the time of burning may have an impact on its postfire recovery. Richburg and others [86,88] evaluated the effectiveness of applying cutting and burning treatments at different times of year in reducing sprout "vigor" for 7 woody invasive species including Japanese barberry. All treatments, regardless of timing, reduced Japanese barberry cover for over 1 year, with a decrease of nearly 90% in treatments that included a burn [86,88]. Japanese barberry sprout height, biomass, and density were generally similar between cut plots and burned plots but were not compared to control plots . Although differences were not significant, total nonstructural carbohydrate (TNC) levels were lower than controls in the April-treated Japanese barberry and remained depleted throughout the growing season. Any depleted TNC in treated plants returned to levels comparable to those of the control plots after 1 growing season without treatments. Species richness did not appear to be affected by treatments .
In the Berkshire region of western Massachusetts, Japanese barberry occurs on 2 parcels owned by The Nature Conservancy: The Bartholomew site is a mature deciduous forest dominated by sugar maple, black birch, and white ash, with an understory dominated by Japanese barberry, with an average cover of 70%. No other species had a cover value above 10% in Japanese barberry thickets. The Bear Rock site is a forested swamp dominated by white ash and red maple with an understory dominated by Morrow's honeysuckle with Japanese barberry and other nonnative shrubs as common associates. Four plots at each site were randomly assigned to 1 of 4 understory treatments in 2001: 1) untreated control, 2) dormant-season burn (or cut if unable to burn), 3) growing-season cut and burn combination, and 4) repeated growing-season cuts. All growing-season treatments were cut again in 2002. The "dormant-season" burn at the Bartholomew site was conducted on 19 April 2002, after leaf-out of Japanese barberry. Therefore, this should be considered a growing-season treatment for Japanese barberry. Researchers were unable to ignite Japanese barberry slash in treated stands during the growing season (August). However, burning was accomplished in November of the same year [86,88].
Following treatments at the Bartholomew site, Japanese barberry cover decreased to less than 6% in the plots that included burning, but only decreased by about one-third (to 23% cover) in the cut-only plot. At the Bear Rock site, Japanese barberry cover declined following treatments, with the greatest declines in growing-season-treated plots [86,88].
|Percent cover of Japanese barberry before and after cutting and burning treatments at 2 sites in Massachusetts [86,88]|
Cut (6 July 2001)
Cut (6 July 2001)
|Bartholomew (upland forest)||2001*||80.9||83.3||85.9||31.3|
|Cut (10 July 2001)
Burn (18 Nov 2001)
Cut (13 June 2002)
Cut (24 July 2002)
|Cut (10 July 2001)
Cut (13 June 2002)
Cut (24 July 2002)
(12 April 2002)
|*Pretreatment measures conducted
prior to initial treatment.
**Posttreatment measures conducted 20 August and 21 September.
Japanese barberry sprout height, biomass, and density were compared among treated plots but were not compared to control plots. At Bear Rock, Japanese barberry sprout heights were generally similar on growing-season treatment plots, while the dormant-season cut had the tallest sprout heights . Dormant- season-treated Japanese barberry plants had more than 6 times the biomass of the growing-season-treated plants, a result that cannot be explained solely by the difference in amount of growing time before harvest. Japanese barberry sprout density was similar among all treated sites .
Although differences were not significant, TNC levels were lower than controls in April-treated Japanese barberry and remained depleted throughout the growing season. TNC levels in treated plants returned to levels similar to those in untreated control plants after 1 growing season without treatments [86,88].
Species richness and understory species cover did not change at the Bartholomew site after treatment. Richness values were not given for the Bear Rock site [86,88].
|Species richness (number of species) before and after cutting and burning treatments at Bartholomew [86,88]|
Cut (6 July 2001)
Cut (6 July 2001)
|*Pretreatment measures conducted
prior to initial treatment.
**Posttreatment measures conducted 20 August and 21 September.
FIRE MANAGEMENT CONSIDERATIONS:
Potential for postfire establishment: Although only one study was found for this review that reports postfire establishment of Japanese barberry , managers should be alert to this possibility given the ability of Japanese barberry to establish in early successional environments (see Establishment and persistence in early succession).
Using prescribed fire to control Japanese barberry: A review by Johnson  suggests that prescribed fire has successfully reduced Japanese barberry populations in midwestern oak savannas. Similarly, a review by Huebner  suggests that Japanese barberry may be reduced in community importance after repeated (annually consecutive for at least 2 to 5 years) growing-season (spring to early summer) fires. Japanese barberry response to repeated prescribed fires or prescribed fires in oak savannas are not documented elsewhere in the available literature as of 2008.
Richburg and others  suggest that an ideal treatment scenario to control woody invasives would include cutting early in the growing season followed by burning later in the season but before sprouting plants have fully recovered their root TNC reserves. This would force the plants to sprout again and further deplete their reserves. If the fire treatment occurs in mid- to late summer, plants would enter the dormant season with substantially reduced potential for "vigorous" growth the next spring. Reserves can be further depleted by treating multiple times during the growing season, although several years of treatments would still be required. The limit to the number of treatments applied depends on how quickly the target species can resprout and the period of time over which it will continue to resprout before going dormant. Generally, the first treatment should be mechanical followed by a prescribed burn to remove slash. Removal treatments after fire would have to be mechanical, because the prescribed burn would leave insufficient fine fuels to allow a second burn within the same season. Japanese barberry leafs out much earlier than native species. Therefore, it may be possible to apply an early spring treatment after root carbohydrate depletion begins in Japanese barberry but prior to depletion of native species’ reserves (review by ).
The 2 sites in Massachusetts studied by Richburg and others [86,88] are managed for rare plant and animal habitat including an intensive program to eradicate nonnative species. Management plans include utilizing fire where practicable to control invasives and/or maintain habitat structure. The invaded sites are in areas where fine fuels decompose quickly and fires rarely burn, so a prescribed fire is not always possible. A "dormant-season" prescribed fire was accomplished in early April at the Bartholomew site, at which time Japanese barberry had already leafed out while the native species had not. Japanese barberry did not burn in the growing season even when cut in advance. Mechanical treatments such as cutting can increase the fuel load, after which prescribed fire may be used to reduce slash or to clear out thick brush to make additional control methods easier to apply. However, fuels were too sparse after cutting Japanese barberry in July 2001 to carry fire in August 2001. A second attempt at burning was successfully completed after leaf fall in November 2001 . Fuel characteristics and fire behavior at this site are shown in the tables below.
|Japanese barberry fuel loads for untreated (control) and treated (cut) plots calculated from 40 × 40 cm harvest plots |
|Flame length and rate of spread for head fires in Japanese barberry fuels in untreated (control) and cut plots |
|Treatment||Burn date||Flame Length (ft)||Rate of Spread (ft/min)|
Fuel models: Custom fuel models
were constructed for Japanese barberry under 3 conditions: untreated control,
growing-season cut, and dormant-season cut. The custom fuel model predicted fire
behavior well in the dormant season, but predicted greater flame length and rate
of spread than was observed in the growing season. Generally, these
custom fuel models did not perform any better than standard fuel models for
predicting fire behavior in Japanese barberry. See Richburg and others  for
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
IMPORTANCE TO WILDLIFE AND LIVESTOCK:
Information on use of Japanese barberry by livestock and wildlife is limited and comes primarily from reviews. One account suggests that it is "little browsed by livestock" . The Exotic Plants Committee of the New York Chapter of The Wildlife Society includes Japanese barberry in the group of nonnative plant species that provide "some value as wildlife food and cover" . Austin and Hash  classify Japanese barberry as "highly preferred by mule deer". However, other reviews suggest that white-tailed deer dislike Japanese barberry and selectively browse on associated native species [95,115]. According to Ehrenfeld , Japanese barberry has become a favored landscaping plant because of the unpalatability of its foliage to deer. However, she also suggests that dense populations of white-tailed deer in the Northeast may be agents of long-distance dispersal of Japanese barberry fruits , because hoofed browsers, especially white-tailed deer, eat barberries (Berberis spp.) "freely"  and are known to disperse fruits of other Berberis species in western North America .
The bright-colored fruits of Japanese barberry are available to birds throughout winter in the eastern United States, although some birds may eat them only when other foods are scarce or absent . However, wild turkey and grouse utilize Japanese barberry fruit heavily (Wolgast, personal communication cited in ), and recent increases in wild turkey populations may contribute to Japanese barberry spread . A study in central New Jersey documented Japanese barberry seed in the feces and stomachs of several native frugivorous birds. Particular species that ate Japanese barberry were not distinguished. Relative use of all nonnative species in fall was 0.4% to 14% and increased to about 50% in winter. Thus, the predominant use of nonnative fruits occurred after peak bird migration and may therefore be less well-matched to local dispersal than fruits of native plants .
Forest sites invaded by Japanese barberry may provide more favorable tick habitat than uninvaded forest sites. Abundance of Ixodes scapularis, which is a vector for lyme disease, was greater in the presence of Japanese barberry, winterberry holly (Ilex verticillata), and honeysuckle (Lonicera spp.) than in the presence of eastern hemlock (Tsuga canadensis) saplings in second-growth mixed and deciduous forests in Maine. This association held true despite variation in abundance of white-tailed deer, the host for the reproductive stage of I. scapularis .
Cover value: Veeries build nests in Japanese barberry more often than in any other substrate in forests of southeastern New York. Ground nests are second most common. Predation rates did not differ between nests in Japanese barberry and those in native shrubs, but predation rates were higher in nests on the ground than in nests in either shrub type . In a study examining 4,085 gray catbird nests over a 27-year period (1934-1960) in Michigan, Ohio, Kentucky, and Ontario, 138 nests (3.4% of the nests observed) were located in Japanese barberry shrubs .OTHER USES:
A close relative of Japanese barberry, common barberry, was historically used as a substitute for the popular medicinal plant, goldenseal (Hydrastis canadensis). Roots of both plants are rich in several alkaloids, including berberine. A study comparing alkaloid content and antibacterial activity of Japanese barberry with those of common barberry and goldenseal revealed that alcohol extracts of all 3 plants exhibit activity against bacteria associated with sore throats (Streptococcus pyogenes) and opportunistic skin infections (Staphylococcus aureus). This supports the traditional uses of these plants for wound healing and for soothing minor mouth and throat irritations. The results suggest that with respect to its berberine content and in vitro antibacterial activity, Japanese barberry is a potential substitute for goldenseal, which is classified as threatened or endangered in many of its natural habitats due to overharvesting and loss of habitat . Commercial applications of these findings, with regard to Japanese barberry, are being explored in Maine .IMPACTS AND CONTROL:
Japanese barberry invasion can alter soil microbial composition and increase nitrate concentrations [51,53,55]. High nitrate concentrations may result in higher nitrogen losses due to leaching or might make these sites more susceptible to invasion by other weedy plants. The researchers suggest that even if Japanese barberry is removed, "it is very likely that differences in the soils will persist for a prolonged period after that, which might significantly impede the restoration of native flora in the cleared sites" .
One study also provides evidence that invaded sites support more biomass in the shrub layer than uninvaded sites . There is concern that additional biomass in invaded stands may increase the likelihood of fire in those stands  (see Fuels), although this did not seem to be the case during the growing season on sites studied in Massachusetts [86,88] (see Fire Management Considerations).
Control: Information presented in the following sections comes primarily from literature reviews and may not be comprehensive. It is intended to contribute to understanding disturbance adaptations of Japanese barberry and to present considerations for the context of fire management. For more detailed information on control of Japanese barberry, go to individual references cited here or to local extension services.
Japanese barberry may be best controlled by preventing its establishment and by eliminating small, newly expanding populations . Individual Japanese barberry plants may be controlled by handpulling or digging, as it has a shallow root system [45,100]. However, this method is difficult and time consuming  and it is important to remove as much of the underground material as possible because Japanese barberry is likely to sprout from rhizomes left in the soil. Sprouts may be controlled by pulling or herbicide applications . Pulling common barberry in the early 1900s effectively eradicated it from many sites .
Japanese barberry is especially easy to see in the winter and early spring before deciduous plants leaf out. If plants have fruit present, they should be bagged and disposed of to prevent seed dispersal .
Prevention: Prohibiting the commercial sale and planting of Japanese barberry may help limit the establishment and spread of new populations . Native alternatives include coastal sweet pepperbush (Clethra alnifolia) and northern spicebush (Lindera benzoin) .
Observations by Ehrenfeld  suggest that Japanese barberry spreads into relatively undisturbed forests from forest edges. Forest reserves less than 2,400 to 4,900 acres (1,000-2,000 ha) in size would be especially vulnerable to invasion because of their large perimeter to area ratios . Maintaining large forest and natural areas uninterrupted by roads and development may help prevent the establishment and spread of Japanese barberry and other invasive species.
Integrated management: Information on integrating mechanical control (cutting) with prescribed burning is presented in the Fire Management Considerations section. Some combinations of mechanical and chemical control are described in the following sections.
Physical/mechanical: Handpulling is an effective method of reducing Japanese barberry populations and seed production, and it can be done during most of the year. It is most effective for small Japanese barberry plants and small populations . Older shrubs can be dug when soil is moist . When pulling Japanese barberry by hand or removing by other mechanical methods, it is important to remove as much of the root system as possible and to minimize soil disturbance [45,95]. Shrubs can be cut at the base in winter or spring instead of digging, and herbicide can then be used on resprouts. Once removed from old field habitats, regular mowing may prevent reestablishment [45,100]. Repeated mowing or cutting controls the spread of Japanese barberry but does not eradicate it. Stems need to be cut at least once per growing season, as close to ground level as possible. Hand-cutting of established clumps is difficult and time consuming due to the long, arching stems and prolific thorns .
Fire: See Fire Management Considerations.
Biological: A review by Silander and Klepis  suggests that there may be some potential for biological control of Japanese barberry using nonnative tephritid flies, though the potential for biocontrol has not been studied for this species in North America.
Chemical: Treatment with systemic herbicides like glyphosate and triclopyr has been effective for controlling Japanese barberry (review by ). The Southeast Exotic Pest Plant Council  suggests that large thickets of Japanese barberry may be foliar sprayed with herbicides such as glyphosate or triclopyr in areas where risk to nontarget species is minimal. They recommend using the cut-stump method (cutting stems at or near ground level and applying herbicide to the stump) when the ground is not frozen. The cut-stump method is especially useful where the presence of desirable species precludes foliar application. Glyphosate is most effective for controlling Japanese barberry when applied in early spring at leaf out, when little else is in leaf .
Cultural: No information is available on this topic.
OTHER MANAGEMENT CONSIDERATIONS:
Climate change: Studies and related models from oak-dominated, second-growth, Japanese barberry-invaded forests in the northeastern United States suggest possible implications of global warming in these communities. The investigators suggest that warming in southern New York would benefit the net carbon gain of mountain-laurel relative to Japanese barberry and may therefore limit the displacement of native shrubs by Japanese barberry. Conversely, increased regional nitrogen deposition along with pronounced winter warming may enhance carbon gain in Japanese barberry relative to native shrubs and contribute to Japanese barberry invasiveness. More information is needed to determine the role that climate change may play in Japanese barberry invasion in northeastern deciduous forests. Models based on these data predict that the annual foliar carbon loss has increased since the early 20th century by 12.9%, 10.3%, and 8.9% for Japanese barberry, mountain-laurel, and highbush blueberry, respectively [118,119,120]. See the Seasonal Development section for more details of this research.
1. Austin, D. D; Hash, A. B. 1988. Minimizing browsing damage by deer: landscape planning for wildlife. Utah Science. 49(3): 66-70. 
2. Barringer, Kerry; Clemants, Steven E. 2003. The vascular flora of Black Rock Forest, Cornwall, New York. Journal of the Torrey Botanical Society. 130(4): 292-308. 
3. Barton, Andrew M.; Brewster, Lauri B.; Cox, Anne N.; Prentiss, Nancy K. 2004. Non-indigenous woody invasive plants in a rural New England town. Biological Invasions. 6: 205-211. 
4. Barton, Lela V. 1954. Effect of presoaking on dormancy of seeds. Contributions from Boyce Thompson Institute. 17(7): 435-438. 
5. Baskin, Carol C.; Baskin, Jerry M. 2001. Seeds: ecology, biogeography, and evolution of dormancy and germination. San Diego, CA: Academic Press. 666 p. 
6. Baskin, Carol C.; Baskin, Jerry M.; Meyer, Susan E. 1993. Seed dormancy in the Colorado Plateau shrub Mahonia fremontii (Berberidaceae) and its ecological and evolutionary implications. The Southwestern Naturalist. 38(2): 91-99. 
7. Bellemare, Jesse; Motzkin, Glenn; Foster, David R. 2002. Legacies of the agricultural past in the forested present: an assessment of historical land-use effects on rich mesic forests. Journal of Biogeography. 29(10/11): 1401-1420. 
8. Braun, E. Lucy. 1989. The woody plants of Ohio. Columbus, OH: Ohio State University Press. 362 p. 
9. Brothers, Timothy S.; Spingarn, Arthur. 1992. Forest fragmentation and alien plant invasion of central Indiana old-growth forests. Conservation Biology. 6(1): 91-100. 
10. Butler, Brett J.; Barclay, John S.; Fisher, Jeffrey P. 1999. Plant communities and flora of Robins Island (Long Island), New York. Journal of the Torrey Botanical Society. 126(1): 63-76. 
11. Cassidy, Timothy M. 2002. Effects of soil acidity and resource availability on the growth of Japanese barberry (Berberis thunbergii). Amherst, MA: University of Massachusetts. 49 p. Thesis. 
12. Cassidy, Timothy M.; Fownes, James H.; Harrington, Robin A. 2004. Nitrogen limits and invasive perennial shrub in forest understory. Biological Invasions. 6: 113-121. 
13. Chapman, William K.; Bessette, Alan E. 1990. Trees and shrubs of the Adirondacks. Utica, NY: North Country Books, Inc. 131 p. 
14. D'Appollonio, Jennifer. 2006. Regeneration strategies of Japanese barberry (Berberis thunbergii DC.) in coastal forests of Maine. Orono, ME: The University of Maine. 93 p. Thesis. 
15. Davidson, Donald W.; Buell, Murray F. 1967. Shrub and herb continua of upland forests of northern New Jersey. The American Midland Naturalist. 77(2): 371-389. 
16. Davis, Mark A.; Grime, J. Philip; Thompson, Ken. 2000. Fluctuating resources in plant communities: a general theory of invasibility. Journal of Ecology. 88(3): 528-534. 
17. Davis, Opal Hart. 1927. Germination and early growth of Cornus florida, Sambucus canadensis, and Berberis thunbergii. Botanical Gazette. 84(3): 225-263. 
18. Davison, Sara E.; Forman, Richard T. T. 1982. Herb and shrub dynamics in a mature oak forest: a thirty-year study. Bulletin of the Torrey Botanical Club. 109(1): 64-73. 
19. Decker, Daniel J.; Enck, Jody W., eds. 1987. Exotic plants with identified detrimental impacts on wildlife habitats in New York State. Natural Resources Research and Extension Series 29. Ithaca, NY: The Wildlife Society, New York Chapter. 56 p. 
20. DeGasperis, Brian G.; Motzkin, Glenn. 2007. Windows of opportunity: historical and ecological controls on Berberis thunbergii invasions. Ecology. 88(2): 3115-3125. 
21. Dibble, Alison C.; Rees, Catherine A. 2005. Does the lack of reference ecosystems limit our science? A case study in nonnative invasive plants as forest fuels. Journal of Forestry. 103(7): 329-338. 
22. Dibble, Alison C.; White, Robert H.; Lebow, Patricia K. 2007. Combustion characteristics of north-eastern USA vegetation tested in the cone calorimeter: invasive versus non-invasive plants. International Journal of Wildland Fire. 16(4): 426-443. 
23. Doran, William L. 1957. Propagation of woody plants by cuttings. Experiment Station Bulletin No. 491. Amherst, MA: University of Massachusetts, College of Agriculture. 99 p. 
24. Dorn, Robert D. 1988. Vascular plants of Wyoming. Cheyenne, WY: Mountain West Publishing. 340 p. 
25. Dunn, Christopher P. 1986. Shrub layer response to death of Ulmus americana in southeastern Wisconsin lowland forests. Bulletin of the Torrey Botanical Club. 113(2): 142-148. 
26. Ehrenfeld, Joan G. 1997. Invasion of deciduous forest preserves in the New York Metropolitan region by Japanese barberry (Berberis thunbergii DC.). Journal of the Torrey Botanical Society. 124(2): 210-215. 
27. Ehrenfeld, Joan G. 1999. Structure and dynamics of populations of Japanese barberry (Berberis thunbergii DC.) in deciduous forests of New Jersey. Biological Invasions. 1: 203-213. 
28. Ehrenfeld, Joan G. 2004. Implications of invasive species for belowground community and nutrient processes. Weed Technology. 18: 1232-1235. 
29. Ehrenfeld, Joan G.; Kourtev, Peter; Huang, Weize. 2001. Changes in soil functions following invasions of exotic understory plants in deciduous forests. Ecological Applications. 11(5): 1287-1300. 
30. Eschtruth, Anne K.; Cleavitt, Natalie L.; Battles, John J.; Evans, Richard A.; Fahey, Timothy J. 2006. Vegetation dynamics in declining eastern hemlock stands: 9 years of forest response to hemlock woolly adelgid infestation. Canadian Journal of Forest Research. 36: 1435-1450. 
31. Fahey, Timothy J.; Reiners, William A. 1981. Fire in the forests of Maine and New Hampshire. Bulletin of the Torrey Botanical Club. 108: 362-373. 
32. Fike, Jean; Niering, William A. 1999. Four decades of old field vegetation development and the role of Celastrus orbiculatus in the northeastern United States. Journal of Vegetation Science. 10(4): 483-492. 
33. Filip, Stanley M.; Little, Elbert L., Jr. 1971. Trees and shrubs of the Bartlett Experimental Forest, Carroll County, New Hampshire. Res. Pap. NE-211. Upper Darby, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 20 p. 
34. Flora of North America Association. 2008. Flora of North America: The flora, [Online]. Flora of North America Association (Producer). Available: http://www.fna.org/FNA. 
35. Flory, S. Luke; Clay, Keith. 2006. Invasive shrub distribution varies with distance to roads and stand age in eastern deciduous forests in Indiana, USA. Plant Ecology. 184: 131-141. 
36. Gleason, Henry A.; Cronquist, Arthur. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. 2nd ed. New York: New York Botanical Garden. 910 p. 
37. Glitzenstein, Jeff S.; Canham, Charles D.; McDonnell, Mark J.; Streng, Donna R. 1990. Effects of environment and land-use history on upland forests of the Cary Arboretum, Hudson Valley, New York. Bulletin of the Torrey Botanical Club. 117(2): 106-122. 
38. Hann, Wendel; Havlina, Doug; Shlisky, Ayn; [and others]. 2005. Interagency fire regime condition class guidebook. Version 1.2, [Online]. In: Interagency fire regime condition class website. U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior; The Nature Conservancy; Systems for Environmental Management (Producer). Variously paginated [+ appendices]. Available: http://www.frcc.gov/docs/22.214.171.124/Complete_Guidebook_V1.2.pdf [2007, May 23]. 
39. Harrington, Robin A.; Fownes, James H.; Cassidy, Timothy M. 2004. Japanese barberry (Berberis thunbergii) in forest understorey: leaf and whole plant responses to nitrogen availability. The American Midland Naturalist. 151(2): 206-216. 
40. Howard, Lauren F.; Lee, Thomas D. 2002. Upland old-field succession in southeastern New Hampshire. Journal of the Torrey Botanical Society. 129(1): 60-76. 
41. Huebner, Cynthia D. 2006. Fire and invasive exotic plant species in eastern oak communities: an assessment of current knowledge. In: Dickinson, Matthew B., ed. Fire in eastern oak forests: delivering science to land managers, proceedings of a conference; 2005 November 15-17; Columbus, OH. Gen. Tech. Rep. NRS-P-1. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station: 218-232. 
42. Hughes, H. Glenn. 1989. Use of native shrubs on strip-mined lands in the humid East. In: Wallace, Arthur; McArthur, E. Durant; Haferkamp, Marshall R., compilers. Proceedings--symposium on shrub ecophysiology and biotechnology; 1987 June 30 - July 2; Logan, UT. Gen. Tech. Rep. INT-256. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 70-73. 
43. Hughes, H. Glenn. 1990. Ecological restoration: fact or fantasy on strip-mined lands in western Pennsylvania? In: Hughes, H. Glenn; Bonnicksen, Thomas M., eds. Restoration '89: the new management challenge: Proceedings, 1st annual meeting of the Society for Ecological Restoration; 1989 January 16-20; Oakland, CA. Madison, WI: The University of Wisconsin Arboretum; Society for Ecological Restoration: 237-243. 
44. Hunter, John C.; Mattice, Jennifer A. 2002. The spread of woody exotics into the forests of a northeastern landscape, 1938-1999. Journal of the Torrey Botanical Society. 129(3): 220-227. 
45. Johnson, Elizabeth. 1996. Berberis thunbergii--Japanese barberry. In: Randall, John M.; Marinelli, Janet, eds. Invasive plants: Weeds of the global garden. Handbook #149. Brooklyn, NY: Brooklyn Botanic Garden: 47. 
46. Johnson, Vanessa S.; Litvaitis, John A.; Lee, Thomas D.; Frey, Serita D. 2006. The role of spatial and temporal scale in colonization and spread of invasive shrubs in early successional habitats. Forest Ecology and Management. 228(1-3): 124-134. 
47. Kartesz, John T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. 1st ed. In: Kartesz, John T.; Meacham, Christopher A. Synthesis of the North American flora (Windows Version 1.0), [CD-ROM]. Chapel Hill, NC: North Carolina Botanical Garden (Producer). In cooperation with: The Nature Conservancy; U.S. Department of Agriculture, Natural Resources Conservation Service; U.S. Department of the Interior, Fish and Wildlife Service. 
48. Kearsley, Jennifer. 1999. Inventory and vegetation classification of floodplain forest communities in Massachusetts. Rhodora. 101(906): 105-135. 
49. Kentucky Exotic Pest Plant Council. 2001. Invasive exotic plant list, [Online]. Southeast Exotic Pest Plant Council (Producer). Available: http://www.se-eppc.org/states/KY/KYlists.html [2005, April 13]. 
50. Koh, S.; Watt, T. A.; Bazely, D. R.; Pearl, D. L.; Tang, M.; Carleton, T. J. 1996. Impact of herbivory of white-tailed deer (Odocoileus virginianus) on plant community composition. Aspects of Applied Biology. 44: 445-450. 
51. Kourtev, P. S.; Ehrenfeld, J. G.; Haggblom, M. 2003. Experimental analysis of the effect of exotic and native plant species on the structure and function of soil microbial communities. Soil Biology and Biochemistry. 35(7): 895-905. 
52. Kourtev, P. S.; Ehrenfeld, J. G.; Huang, W. Z. 1998. Effects of exotic plant species on soil properties in hardwood forests of New Jersey. Water, Air, and Soil Pollution. 105(1/2): 493-501. 
53. Kourtev, P. S.; Ehrenfeld, J. G.; Huang, W. Z. 2002. Enzyme activities during litter decomposition of two exotic and two native plant species in hardwood forests of New Jersey. Soil Biology and Biochemistry. 34(9): 1207-1218. 
54. Kourtev, P. S.; Huang, W. Z.; Ehrenfeld, J. G. 1999. Differences in earthworm densities and nitrogen dynamics in soils under exotic and native plant species. Biological Invasions. 1(2/3): 237-245. 
55. Kourtev, Peter S.; Ehrenfeld, Joan G.; Haggblom, Max. 2002. Exotic plant species alter the microbial community structure and function in the soil. Ecology. 83(11): 3152-3166. 
56. LANDFIRE Rapid Assessment. 2005. Reference condition modeling manual (Version 2.1), [Online]. In: LANDFIRE. Cooperative Agreement 04-CA-11132543-189. Boulder, CO: The Nature Conservancy; U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior (Producers). 72 p. Available: http://www.landfire.gov/downloadfile.php?file=RA_Modeling_Manual_v2_1.pdf [2007, May 24]. 
57. LANDFIRE Rapid Assessment. 2007. Rapid assessment reference condition models, [Online]. In: LANDFIRE. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Lab; U.S. Geological Survey; The Nature Conservancy (Producers). Available: http://www.landfire.gov/models_EW.php [2008, April 18] 
58. Larsen, Soren Ugilt; Eriksen, Erik Nymann. 2004. Delayed release of primary dormancy and induction of secondary dormancy in seeds of woody taxa caused by temperature alternations. Acta Horticulturae. 630: 91-100. 
59. Lebuhn, Gretchen; Anderson, Gregory J. 1994. Anther tripping and pollen dispensing in Berberis thunbergii. The American Midland Naturalist. 131(2): 257-265. 
60. Lehrer, Jonathan M.; Brand, Mark H.; Lubell, Jessica D. 2006. Four cultivars of Japanese barberry demonstrate differential reproductive potential under landscape conditions. HortScience. 41(3): 762-767. 
61. Lehrer, Jonathan Michael. 2007. Horticultural strategies to counter invasive Japanese barberry (Berberis thunbergii DC.). Storrs, CT: University of Connecticut. 141 p. Dissertation. 
62. Lovinger, Sarah; Anisko, Tomasz. 2004. Benign Berberis: Shrub trials at Longwood Gardens help identify Japanese barberry cultivars with limited invasive potential. American Nurseryman. [Chicago, IL]: American Nurseryman Publishing Co. 200(11): 36-39. 
63. Lubelczyk, Charles B.; Elias, Susan P.; Rand, Peter W.; Holman, Mary S.; Lacombe, Eleanor H.; Smith, Robert P., Jr. 2004. Habitat associations of Ixodes scapularis (Acari: Ixodidae) in Maine. Environmental Entomology. 33(4): 900-906. 
64. Lubelczyk, Chuck. 2001. The good, the bad, and the thorny. Watermark. Wells, ME: Laudholm Trust; Wells National Estuarine Research Reserve. 18(3): 6. Available online: http://www.wellsreserve.org/watermark/v18n3p6.pdf [2008, February 27]. 
65. Lundgren, Marjorie R.; Small, Christine J.; Dreyer, Glenn D. 2004. Influence of land use and site characteristics on invasive plant abundance in the Quinebaug Highlands of southern New England. Northeastern Naturalist. 11(3): 313-332. 
66. Mabry, Cathy; Korsgren, Tobe. 1998. A permanent plot study of vegetation and vegetation-site factors fifty-three years following disturbance in central New England, U.S.A. Ecoscience. 5(2): 232-240. 
67. Martin, Alexander C.; Zim, Herbert S.; Nelson, Arnold L. 1951. American wildlife and plants. New York: McGraw-Hill Book Company, Inc. 500 p. 
68. McCarthy, Brian C. 1997. Response of a forest understory community to experimental removal of an invasive nonindigenous plant (Alliaria petiolata, Brassicaceae). In: Luken, James O.; Thieret, John W., eds. Assessment and management of plant invasions. New York: Springer-Verlag: 117-130. 
69. McCauley, Kathleen M.; Crow, Garrett E. 2005. The vegetation and flora of Platt Park, Southbury, Connecticut. Rhodora. 107(930): 186-230. 
70. Medley, Kimberly E. 1997. Distribution of the non-native shrub Lonicera maackii in Kramer Woods, Ohio. Physical Geography. 18(1): 18-36. 
71. Mehrhoff, L. J.; Silander, J. A., Jr.; Leicht, S. A.; Mosher, E. S.; Tabak, N. M. 2003. IPANE: Invasive Plant Atlas of New England, [Online]. Storrs, CT: University of Connecticut, Department of Ecology and Evolutionary Biology (Producer). Available: http://nbii-nin.ciesin.columbia.edu/ipane/ [2008, May 28]. 
72. Missouri Botanical Garden. 2002. Missouri exotic pest plants: Category B, [Online]. Missouri Botanical Garden (Producer). Available: http://www.mobot.org/MOBOT/research/mepp/categoryB.shtml [2004, December 23]. 
73. Mohlenbrock, Robert H. 1986. [Revised edition]. Guide to the vascular flora of Illinois. Carbondale, IL: Southern Illinois University Press. 507 p. 
74. Monk, Ralph W.; Wiebe, Herman H. 1961. Salt tolerance and protoplasmic salt hardiness of various woody and herbaceous ornamental plants. Plant Physiology. 36(4): 478-482. 
75. Monk, Ralph; Peterson, H. B. 1962. Tolerance of some trees and shrubs to saline conditions. Proceedings, American Horticultural Society. 81: 556-561. 
76. Morinaga, Toshitaro. 1926. Effect of alternating temperatures upon the germination of seeds. American Journal of Botany. 13(2): 141-158. 
77. Neumann, David D.; Dickmann, Donald I. 2001. Surface burning in a mature stand of Pinus resinosa and Pinus strobus in Michigan: effects on understory vegetation. International Journal of Wildland Fire. 10: 91-101. 
78. Nickell, Walter P. 1965. Habitats, territory, and nesting of the catbird. The American Midland Naturalist. 73(2): 433-478. 
79. Nowacki, Gregory J.; Abrams, Marc D. 2008. The demise of fire and "mesophication" of forests in the eastern United States. BioScience. 58(2): 123-138. 
80. Oregon State University. 2008. Berberis thunbergii var. atropurpurea--Purple (red) leafed Japanese barberry, [Online]. In: Landscape plants: Images, identification, and information. Volume 1. Corvallis, OR: Department of Horticulture (Producer). Available: http://oregonstate.edu/dept/ldplants/betha.htm [2008, July 3]. 
81. Orwig, David A.; Foster, David R. 1998. Forest response to the introduced hemlock woolly adelgid in southern New England, USA. Journal of the Torrey Botanical Club. 125(1): 60-73. 
82. Ostfeld, Richard S.; Cepeda, Obed M.; Hazler, Kirsten R.; Miller, Michael C. 1995. Ecology of lyme disease: habitat associations of ticks (Ixodes scapularis) in a rural landscape. Ecological Applications. 5(2): 353-361. 
83. Pederson, Brian S.; Wallis, Angela M. 2004. Effects of white-tailed deer herbivory on forest gap dynamics in a wildlife preserve, Pennsylvania, USA. Natural Areas Journal. 24(2): 82-94. 
84. Radford, Albert E.; Ahles, Harry E.; Bell, C. Ritchie. 1968. Manual of the vascular flora of the Carolinas. Chapel Hill, NC: The University of North Carolina Press. 1183 p. 
85. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. 
86. Richburg, Julie A. 2005. Timing treatments to the phenology of root carbohydrate reserves to control woody invasive plants. Amherst, MA: University of Massachusetts, Department of Natural Resources Conservation. 175 p. Dissertation. 
87. Richburg, Julie A.; Dibble, Alison C.; Patterson, William A., III. 2001. Woody invasive species and their role in altering fire regimes of the Northeast and Mid-Atlantic states. In: Galley, Krista E. M.; Wilson, Tyrone P., eds. Proceedings of the invasive species workshop: The role of fire in the control and spread of invasive species; Fire conference 2000: the first national congress on fire ecology, prevention, and management; 2000 November 27 - December 1; San Diego, CA. Misc. Publ. No. 11. Tallahassee, FL: Tall Timbers Research Station: 104-111. 
88. Richburg, Julie A.; Patterson, William A., III; Ohman, Michael. 2004. Fire management options for controlling woody invasive plants in the northeastern and mid-Atlantic U.S., [Online]. Final report: Joint Fire Science Program--Project Number: 00-1-2-06. Joint Fire Science Program, Northeast Barrens Fuels Demonstration Project (Producer). Available: http://www.umass.edu/nebarrensfuels/publications/pdfs/Richburg_Ohman-Invasives_Fire_final_report.pdf [2008, March 4]. 
89. Roland, A. E.; Smith, E. C. 1969. The flora of Nova Scotia. Halifax, NS: Nova Scotia Museum. 746 p. 
90. Schmidt, Kenneth A.; Nelis, Lisa C.; Briggs, Nathan; Ostfeld, Richard S. 2005. Invasive shrubs and songbird nesting success: effects of climate variability and predator abundance. Ecological Applications. 15(1): 258-265. 
91. Seymour, Frank Conkling. 1982. The flora of New England. 2nd ed. Phytologia Memoirs 5. Plainfield, NJ: Harold N. Moldenke and Alma L. Moldenke. 611 p. 
92. Silander, John A., Jr.; Klepeis, Debra M. 1999. The invasion ecology of Japanese barberry (Berberis thunbergii) in the New England landscape. Biological Invasions. 1: 189-201. 
93. Soper, James H.; Heimburger, Margaret L. 1982. Shrubs of Ontario. Life Sciences Miscellaneous Publications. Toronto, ON: Royal Ontario Museum. 495 p. 
94. Southeast Exotic Pest Plant Council, Tennessee Chapter. 2001. Invasive exotic pest plants in Tennessee, [Online]. Athens, GA: University of Georgia; Southeast Exotic Pest Plant Council (Producer). Available: http://www.se-eppc.org/states/TN/TNIList.html [2004, February 12]. 
95. Southeast Exotic Pest Plant Council. 2003. Southeast Exotic Pest Plant Council invasive plant manual, [Online]. Southeast Exotic Pest Plant Council (Producer). Available: http://www.invasive.org/eastern/eppc/index.html [2005, August 10]. 
96. Steffey, Jane. 1985. Strange relatives: the barberry family. American Horticulturalist. 64(4): 4-9. 
97. Stickney, Peter F. 1989. Seral origin of species comprising secondary plant succession in Northern Rocky Mountain forests. FEIS workshop: Postfire regeneration. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT. 10 p. 
98. Strausbaugh, P. D.; Core, Earl L. 1977. Flora of West Virginia. 2nd ed. Morgantown, WV: Seneca Books, Inc. 1079 p. 
99. Swanson, Ann M.; Vankat, John L. 2000. Woody vegetation and vascular flora of an old-growth mixed-mesophytic forest in southwestern Ohio. Castanea. 65(1): 36-55. 
100. Swearingen, J.; Reshetiloff, K.; Slattery, B.; Zwicker, S. 2002. Plant invaders of mid-Atlantic natural areas. [Washington, DC]: U.S. Department of the Interior, National Park Service; Fish and Wildlife Service. 82 p. Available online: http://www.invasive.org/eastern/midatlantic/index.html [2005, September 9]. 
101. Townesmith, Andrew Keith. 2004. The effects of land-use history on the distribution and density of Japanese barberry (Berberis thunbergii). Storrs, CT: University of Connecticut. 64 p. Thesis. 
102. U.S. Department of Agriculture, Forest Service, Eastern Region. 2004. Eastern Region invasive plants ranked by degree of invasiveness, [Online]. In: Noxious weeds and non-native invasive plants. Section 3: Invasive plants. Milwaukee, WI: Eastern Region (Producer). Available: http://www.fs.fed.us/r9/wildlife/range/weed/Sec3B.htm [2004, February 16]. 
103. U.S. Department of Agriculture, Forest Service, Ottawa National Forest. 2003. Ottawa National Forest: Non-native invasive plant program, [Online]. In: Botany information. Ironwood, MI: Ottawa National Forest (Producer). Available: http://www.fs.fed.us/r9/ottawa/forest_management/botany/invasive_folder/index_ottawa_national_forest.htm [2004, August 30]. 
104. U.S. Department of Agriculture, Forest Service, Southern Region. 2001. Regional invasive exotic plant species list, [Online]. In: Regional Forester's list and ranking structure: invasive exotic plant species of management concern. In: Invasive plants of southern states list. Southeast Exotic Pest Plant Council (Producer). Available: http://www.se-eppc.org/fslist.cfm [2003, August 25]. 
105. U.S. Department of Agriculture, Natural Resources Conservation Service. 2008. PLANTS Database, [Online]. Available: http://plants.usda.gov/. 
106. Vankat, John L.; Snyder, Gary W. 1991. Floristics of a chronosequence corresponding to old field-deciduous forest succession in southwestern Ohio. I. Undisturbed vegetation. Bulletin of the Torrey Botanical Club. 118(4): 365-376. 
107. Vermont Agency of Natural Resources. 1998. Invasive exotic plants of Vermont: A list of the state's most troublesome weeds. Vermont Invasive Exotic Plant Fact Sheet Series. Waterbury, VT: Department of Environmental Conservation; Department of Fish and Wildlife, Nongame and Natural Hertiage Program. 2 p. In cooperation with: The Nature Conservancy of Vermont. 
108. Villinski, Jacquelyn R.; Dumas, Elizabeth R.; Chai, Hee-Byung; Pezzuto, John M.; Angerhofer, Cindy K.; Gafner, Stefan. 2003. Antibacterial activity and alkaloid content of Berberis thunbergii, Berberis vulgaris and Hydrastis canadensis. Pharmaceutical Biology. 41(8): 551-557. 
109. Virginia Department of Conservation and Recreation, Division of Natural Heritage. 2003. Invasive alien plant species of Virginia, [Online]. Virginia Native Plant Society (Producer). Available: http://www.dcr.state.va.us/dnh/invlist.pdf [2005, June 17]. 
110. Von Holle, Betsy; Motzkin, Glenn. 2007. Historical land use and environmental determinants of nonnative plant distribution in coastal southern New England. Biological Conservation. 136(1): 33-43. 
111. Voss, Edward G. 1985. Michigan flora. Part II. Dicots (Saururaceae--Cornaceae). Bull. 59. Bloomfield Hills, MI: Cranbrook Institute of Science; Ann Arbor, MI: University of Michigan Herbarium. 724 p. 
112. Webb, Sara L.; Dwyer, Marc; Kaunzinger, Christina K.; Wyckoff, Peter H. 2000. The myth of the resilient forest: case study of the invasive Norway maple (Acer platanoides). Rhodora. 102(911): 332-354. 
113. Webb, Sara L.; Pendergast, Thomas H., IV; Dwyer, Marc E. 2001. Response of native and exotic maple seedling banks to removal of the exotic, invasive Norway maple (Acer platanoides). Journal of the Torrey Botanical Society. 128(2): 141-149. 
114. Wells, Elizabeth Fortson; Brown, Rebecca Louise. 2000. An annotated checklist of the vascular plants in the forest at historic Mount Vernon, Virginia: a legacy from the past. Castanea. 65(4): 242-257. 
115. Westbrooks, Randy G. 1998. Invasive plants: changing the landscape of America. Fact Book. Washington, DC: Federal Interagency Committee for the Management of Noxious and Exotic Weeds. 109 p. 
116. White, Douglas W.; Stiles, Edmund W. 1992. Bird dispersal of fruits of species introduced into eastern North America. Canadian Journal of Botany. 70: 1689-1696. 
117. Wofford, B. Eugene. 1989. Guide to the vascular plants of the Blue Ridge. Athens, GA: The University of Georgia Press. 384 p. 
118. Xu, Cheng-Yuan; Griffin, Kevin L.; Schuster, W. S. F. 2007. Leaf phenology and seasonal variation of photosynthesis of invasive Berberis thunbergii (Japanese barberry) and two co-occurring native understory shrubs in a northeastern United States deciduous forest. Oecologia. 154(1): 11-21. 
119. Xu, Cheng-Yuan; Schuster, W. S. F.; Griffin, Kevin L. 2007. Seasonal variation of temperature response of respiration in invasive Berberis thunbergii (Japanese barberry) and two co-occurring native understory shrubs in a northeastern US deciduous forest. Oecologia. 153(4): 809-819. 
120. Xu, Chengyuan. 2006. Foliar dark respiration: scaling gas exhange characteristics and isotopic signals from leaf to canopy and ecosystem level. New York: Columbia University. 281 p. Dissertation.