|© 2006 Vivian Parker|
According to Cronquist and others , woods strawberry and Virginia strawberry (Fragaria virginiana) do not hybridize in the western U.S., and any similarities in diagnostic traits are more likely attributable to variability within species.
For the purposes of this review, the common name "woods strawberry" is used when discussing
characteristics common to (or assumed to be common to) the species in general. When referring to infrataxa,
the scientific names for the subspecies listed above are used. When referring to multiple Fragaria spp.,
the name "wild strawberries" is used.
FEDERAL LEGAL STATUS:
No special status
Information on state-level protected status of plants in the United States is available at Plants Database.
In Canada, woods strawberry occurs from coastal British Columbia east to Newfoundland [37,61,72,79,80,90,107,125,134,134,173], as well as in Northwest Territories . It also occurs in Baja California, Mexico [37,78,108,175].
Globally, woods strawberry distribution is circumboreal [98,99]. While it is widely considered a native species in North America, at least some populations may originate from introduced European stock [61,111,141], especially in the northeastern United States and adjacent Canada [61,80,134,141], and the northern Great Plains .
Comprehensive surveys examining the presence or absence of woods
strawberry within the following biogeographic vegetation schemes are not available. These lists represent a
"best estimate" of woods strawberry occurrence based on information obtained from floras and other
literature, herbarium samples, and confirmed observations.
FRES10 White-red-jack pine
FRES13 Loblolly-shortleaf pine
FRES21 Ponderosa pine
FRES22 Western white pine
FRES24 Hemlock-Sitka spruce
FRES26 Lodgepole pine
FRES28 Western hardwoods
FRES30 Desert shrub
FRES33 Southwestern shrubsteppe
FRES34 Chaparral-mountain shrub
FRES37 Mountain meadows
FRES38 Plains grasslands
FRES40 Desert grasslands
FRES41 Wet grasslands
STATES/PROVINCES: (key to state/province abbreviations)
Woods strawberry is a low-growing, deciduous perennial herb [6,27,37,62,63,72,73,90,99,108,120,126,145,154, 173,175], with petioles and flowering stems typically arising from a single crown in rosette form. Occasionally a single crown may split into 2 or more crowns by the development of an axillary meristem, but production of leaves and flowers is generally restricted to a single meristematic axis in each ramet . Petioles are generally 0.3 to 6.9 inches (0.8-17.5 cm) long [37,78,80,173], with flowering stems often shorter . Leaves are basal and palmately trifoliate [37,62,63,72,78,79,80,90,99,108,120,141,145,154, 173,175], with leaflets 0.5 to 2.6 inches (1.3-6.5 cm) long and 0.5 to 2.8 inches (1.3- 7.0 cm) wide [37,78,108,145,173], the terminal leaflet being largest [37,173]. Flowers of Fragaria vesca ssp. vesca, F. v. ssp. americana, and F. v. ssp. californica are exclusively perfect, while F. v. ssp. bracteata produces occasional female-only plants . Fleshy fruits are up to 0.4 inch (1 cm) thick and covered with 0.05 inch (1.3-1.4 mm) long achenes [37,62,78,80,108,126,173]. Crowns arise from short rhizomes [63,78,90,99,108,126], spreading and forming colonies by stolons that root and produce plantlets at the nodes [37,47,62,63,72,73,78,80,90,99,108,120,126,145, 154,173,175].RAUNKIAER  LIFE FORM:
Pollination: According to Ostler and Harper , woods strawberry is "animal-pollinated", and flower structure is open with "unrestricted access to nectaries and/or pollen."
Breeding system: Fragaria vesca. ssp. vesca, F. v. ssp. americana, and F. v. ssp. californica have perfect flowers. Fragaria vesca ssp. bracteata is gynodioecious, in which most plants have perfect flowers, but occasionally some plants bear only female flowers .
Seed production: No information is available on this topic.
Seed dispersal: Seeds are probably dispersed by birds and mammals (Martin and others 1951, as cited in ), .
Seed banking: Although information describing longevity of viable, soil-stored woods strawberry seed is sparse, there is some indication that it does develop seed banks ( and references contained therein). Laboratory and field research in Europe indicate that viable woods strawberry seeds may persist in soil for at least 5 years .
It appears that the woods strawberry seed bank is found close to the soil surface. Kramer and Johnson  studied seed banks in Douglas-fir and grand fir forests in west-central Idaho. A total of 19 viable woods strawberry seeds were collected from 12 of 48 stands sampled. Ninety-five percent of viable woods strawberry seeds were found in the 0 to 2 inch (0-5 cm) depth, which was mainly composed of compacted litter and organic layers. Five percent of viable woods strawberry seeds were found in the 2 to 4 inch (5-10 cm) depth, which was predominantly mineral soil . Similarly, of soil samples taken from 3 grand fir-dominated sites in the Blue Mountains of eastern Oregon, 2 sites yielded germinable seeds only from the litter/humus layer, and 1 site only from the 0 to 0.8 inch (0-2 cm) mineral soil layer. No woods strawberry seedlings emerged from the 0.8 to 1.6 inch (2-4 cm) soil samples .
Germination: As of this writing (2007) there is little published information describing conditions either favoring or inhibiting woods strawberry seed germination. Steele and Geier-Hayes  wrote that woods strawberry "germinates on moist mineral soil in partial shade."
Results from a laboratory experiment suggest that cold stratification may induce more rapid germination of woods strawberry seed but provides a much smaller, perhaps negligible effect on eventual numbers of germinants. Woods strawberry seeds were planted in sterilized soil and overwintered in either a coldframe or a heated greenhouse. Seeds overwintered in coldframes were brought indoors after 83 days and had greater germination (45.5%) compared with seeds from the heated greenhouse (32%). Seeds in the cold frame treatment also germinated more rapidly, between 14 and 56 days, while those in the heated greenhouse required between 48 and 252 days for germination .
Seedling establishment/growth: To date (2007), not much information has been published about woods strawberry seedling establishment and growth. However, there is some indication that seedling establishment occurs mainly apart from established populations, perhaps following some type of soil disturbance. A review by Eriksson  suggests that seedling establishment in preestablished populations of adult woods strawberry clones is rare, and that seedlings mainly contribute to establishment of new populations apart from established clones. Anecdotal evidence provided by Jurik  concurs, noting not only that seedlings do not seem to establish in preexisting populations, but that seedlings were observed only where the original vegetation was removed and mineral soil exposed. Steele and Geier-Hayes [148,150,151] noted that woods strawberry seedling establishment apparently requires bare shaded soil.
Asexual regeneration: Vegetative spread in woods strawberry occurs in 3 ways; although, according to a review by Eriksson , woods strawberry vegetative spread is mainly by stolons. Crowns arise from short rhizomes [63,78,90,99,108,126], and stolons arise from axillary buds, with individual ramets producing 1 to 4 stolons per season. Stolons may branch at alternate nodes. The nonbranching nodes produce 1 to 2 small leaves and adventitious root primordia, and will root when contacting moist substratum. Stolons decay over winter. Individual nodes may root up to 3.3 feet (1 m) from the parent ramet. Adventitious roots may also develop in the axils of decayed leaves allowing plants to "creep along the forest floor . . . through the accumulation of several years' decaying leaf bases" .SITE CHARACTERISTICS:
In western North America, woods strawberry also commonly occurs in, but is not always restricted to, wooded or forested habitats. Although comprehensive surveys are lacking, it appears that woods strawberry can be found in all but the driest forest types in the western United States. Woods strawberry occurrence in forested habitats in this region is often associated with relatively recent disturbance. Examples include forest openings [27,62,72,122], roadsides [71,105], and recently cleared or early successional forest  (also see Successional Status below). Woods strawberry occurrence in western North America is also documented in meadows [47,48,49,79,108], open slopes [73,108], prairie-woodland mosaics , forest margins , and margins of meadows . Reed  mentions woods strawberry occurrence in big sagebrush (Artemisia tridentata) habitats in Jackson Hole, Wyoming, although to date (2007) this is the only example encountered for this habitat.
Elevation: In mountainous western North America, woods strawberry occurrence has been reported from a wide range of elevations. Examples of such reports include: "low" to subalpine along the Pacific Northwest coast , "low to middle elevations" in Glacier National Park , and valley bottom to lower subalpine in west-central Montana . Knight and others  indicated that woods strawberry's preferred habitat in the Medicine Bow Mountains of northern Colorado/southern Wyoming is "higher elevation, mesic sites."
The following table lists published accounts of elevation ranges where woods strawberry occurs in western North America. These examples are not necessarily elevational limits to woods strawberry distribution, but rather a range of elevations, particularly upper elevations, where woods strawberry might occur.
|east-central and southeastern Arizona||7,000 to 9,500 feet (2,100-2,900 m) |
|southeastern Arizona||>9,200 feet (2,800 m) |
|southern Arizona||7,900 to 8,000 feet (2,400 m) |
|California||100 to 6,500 feet (30-2,000 m) |
|Sierra Nevada Range, California||<6,000 feet (1,800 m) |
|Colorado||5,000 to 9,500 feet (1,500-2,900 m) |
|near Crested Butte, Colorado||8,500 to 12,500 feet (2,600-3,800 m) |
|west-central Idaho||5,000 to 7,800 feet (1,500-2,400 m) |
|New Mexico||6,500 to 10,000 feet (2,000-3,000 m) |
|Utah||6,000 to 10,500 feet (1,800-3,200 m) |
|Uinta Basin, Utah||7,000 to 10,500 feet (2,100-3,200 m) |
|Cascade and Olympic Mountains, Washington||up to 4,000 feet (1,200 m) [79,80]|
|northwestern Wyoming||7,900 feet (2,400 m) |
|Intermountain West||5,900 to 7,900 feet (1800-2400 m) |
|Yellowstone National Park||6,000 to 7,600 feet (1,800-2,300 m) |
|Baja California||"higher foothills to about" 8,200 feet (2,500 m) |
The following table provides woods strawberry distribution data by elevation in the Siskiyou Mountains of Oregon and California, and is adapted from .
|Elevation range (feet)||1,500-2,500||2,500-3,500||3,500-4,500||4,500-5,500||5,500-6,300||6,300-7,000|
|Percent frequency of occurrence||0.6||1.1||5.9||10.2||7.0||4.5|
As of this writing (2007) there is no published information regarding elevation and woods strawberry distribution in eastern North America.
Moisture: Based on general information contained in site
descriptions, habitat types, etc., it appears that woods strawberry occurs under a wide range of
moisture conditions, although it is probably not tolerant of extremely wet or dry conditions. Although
comprehensive, rangewide information about moisture conditions for woods strawberry habitat is lacking, the
following descriptions provide some guidelines, at least for parts of the western United States. Lackschewitz
 indicated that woods strawberry occurs on sites in west-central Montana that are mesic (adequate moisture
during all or most of the growing season, but rarely if ever flooded) to meso-xeric (moisture abundant in the
early growing season but dry later on). Franklin and Dyrness  indicated that woods strawberry is more common
in warm, dry forests, less common in cool, moist forests, and rare to nonexistent in cold, moist forests of the
South Umpqua River valley, western Oregon.
Although evidence is limited, it appears that woods strawberry is most prevalent in early successional forests in the western United States. Nevertheless, it also appears that it may be found in most, if not all, successional stages of forest development, at least within some western forest types. For example, Antos and Habeck  sampled vegetation in grand fir-dominated communities in the Swan Valley, western Montana. Average woods strawberry percent occurrence was significantly (P<0.05) greater in stands less than 90 years old (67%), compared with stands greater than 150 years old (7%) . Habeck  also studied succession in western redcedar (Thuja plicata)-western hemlock (Tsuga heterophylla) zone forest communities in Glacier National Park. Woods strawberry exhibited its greatest presence in the earliest stages of succession in this zone, where forests that had established following fire were dominated by Rocky Mountain lodgepole pine (Pinus contorta var. latifolia) and, to a lesser extent, western larch (Larix occidentalis). Woods strawberry diminished in importance in later-successional communities where western redcedar and western hemlock were dominant . Spies  found that mean woods strawberry percent frequency of occurrence in the Oregon Cascades was significantly (P<0.05) lower in old-growth (mean age = 395 years) forest stands, compared with mature (mean age = 115 years) or young (mean age = 60 years) stands. However, Steele and Geier-Hayes [147,148,149,150,151,152] characterized woods strawberry as a midseral species in several Douglas-fir- and grand fir-dominated habitat types in Idaho, and Ross and Hunter  included woods strawberry among "dominants in the climax vegetation" of the western redcedar-western hemlock association in Montana.
Several sources suggest or demonstrate that woods strawberry presence in western forest habitats is enhanced by disturbance. Hall  indicated that wild strawberries tend to increase with site disturbance in the Blue Mountains of eastern Oregon and southeastern Washington. Ferguson and others  indicated that woods strawberry increased substantially in response to both partial and total overstory removal in grand fir-dominated sites in northern Idaho and southeastern Oregon. Green and Jensen  noted that stands of grand fir (grand fir/wild ginger (Asarum caudatum) habitat type) that were subjected to clearcutting, broadcast burning, and high-intensity mechanical scarification resulted in a woods strawberry-thistle (Cirsium spp.) successional community. Nelson and Halpern  studied the responses of understory plants to aggregated retention harvests in 70 to 80-year-old and 110 to 140-year-old Douglas-fir-dominated forests on the western slope of the Cascade Range, southwestern Washington. Aggregates were 2.5 acres (1 ha), with 5 aggregates retained per 32-acre (13 ha) harvest unit. Sampling did not detect woods strawberry in preharvest plots of either the harvested or retention treatments, nor in postharvest retention units 1 to 2 years after cutting. However, woods strawberry was sampled at 3% frequency in harvested areas, with mean cover less than 0.05% . A thinning experiment in a central Colorado Rocky Mountain lodgepole pine forest showed that woods strawberry cover was significantly (P<0.05) greater 5 years after heavy thinning (average basal area 30 ft²/acre), compared with moderate thinning (58 ft²/acre), light thinning (73 ft²/acre), and unthinned controls (basal area not reported) .
It is not clear if observed increases in woods strawberry associated with site disturbance are due to seedling establishment that is promoted by litter layer and soil disturbance (see Seedling Establishment/Growth). It is also possible that extant woods strawberry populations are released from competition for light by disturbance-induced changes in canopy structure, and expand their coverage by vegetative spread (see Asexual Regeneration). Although Kemball and others  considered woods strawberry to be shade intolerant, Steele and Geier-Hayes  indicated that woods strawberry is more shade tolerant than many of the early seral herb-layer species with which it is often associated in Idaho forests, and that it, along with Virginia strawberry, achieves its greatest coverage "beneath a light canopy of trees or tall shrubs where partial shade has reduced competition from earlier successional herbs" .SEASONAL DEVELOPMENT:
|east-central/southeastern Arizona ||X||X||X||X||X|
|near Moscow, Idaho ||X||X|
|northern Idaho ||X||X||X|
|New Mexico ||X||X||X||X||X||X|
|western North Carolina ||X||X||X|
|western Oregon/southwestern Washington ||X||X||X|
|Uinta Basin, Utah ||X||X|
|West Virginia ||X||X||X|
|Blue Ridge Mountains ||X||X||X|
|northern Great Plains ||X||X|
|Intermountain West ||X||X|
|New England ||X||X|
|northeastern United States ||X||X||X|
|coastal, New York to Newfoundland ||X||X||X||X|
|Baja California ||X||X||X||X|
Reported dates for ripe fruits include mid-June to early August near Moscow, Idaho , and by early July in central New York . Stolon production occurs from early June to late August in central New York  and early May through August near Ithaca, New York . Stolon decay begins in late summer and connection between nodes is usually lost by spring, at least in central New York .
Leaf production occurs continuously from April to October in central New York, and a few leaves may overwinter . Steele and Geier-Hayes [150,151] also reported that at least some woods strawberry leaves remain green through the winter in Idaho.
Schmidt and Lotan  reported the following phenological data for woods strawberry from locations east of the Continental Divide in Montana and in Yellowstone National Park, 1928-1937:
|First appearance||Leaves full grown||Flowers start||Flowers end||Fruits ripe||Seed fall starts||Leaves start to color||Leaves fallen|
There is also some suggestion that, at least at the population level, woods strawberry is adapted to fire-prone habitats due to a propensity for postfire seedling establishment. In a study of postfire plant cover in northeastern Oregon, Johnson  indicated that in postfire year 5, woods strawberry established by seed dispersed from outside the measurement plots in a grand fir-pinegrass habitat type. Suggestions that woods strawberry seedling establishment is generally benefited by some type of disturbance (see Seedling Establishment and Growth and Successional Status) also supports the hypothesis that woods strawberry seedling establishment is promoted by fire. In addition, Strickler and Edgerton  suggested that heat may promote woods strawberry seed germination, but a small sample size provided limited experimental evidence.
Although several sources have suggested that seedling establishment and vegetative spread typically do not occur together concurrently, at least within established populations (see Seedling Establishment and Growth), Ahlgren [3,4] observed both woods strawberry seedling establishment and vegetative sprouting, in about equal numbers, in postfire experiment plots in northeastern Minnesota.
Fire regimes: As of this writing (2007), there is little published information linking woods strawberry with specific fire regimes. To the extent that woods strawberry benefits from fire (see Fire Effects), and to the extent that other postfire site characteristics are suitable for its occurrence, it is reasonable to suggest that woods strawberry is likely to be found in areas that experience moderately frequent, relatively low-severity fires. For example, Atzet and McCrimmon  described the fire regime of an Oregon white oak/woods strawberry habitat type in the southern Oregon Cascades as follows: "Fire occurred on three of the four sites sampled. Frequency is high, intensity is low, and many fires are confined to the type, without entering adjacent dense forest sites. Spread rates are moderated by the gentle topography. Heavy fuel production is low, but flashy fuels (grasses) are abundant and dry early in the summer. Vertical and horizontal fuel distribution is discontinuous and varied. Surface area, except for the grasses, is low" .
This is not to suggest that woods strawberry does not occur in areas with starkly different fire regimes than described above. For instance, it may be found in plant communities and ecosystems where the predominant disturbance type is something other than fire, such as windthrow, that may nevertheless benefit woods strawberry (see Successional Status). Given its apparent ubiquity across North America (see Distribution and Occurrence), fire regime is likely just one of many factors influencing woods strawberry occurrence and abundance.
The following table provides fire return intervals for plant communities and ecosystems where woods strawberry likely occurs (although precise distribution information is limited). For further information about specific fire regimes, see the FEIS review(s) of the dominant species listed below.
|Community or Ecosystem||Dominant Species||Fire Return Interval Range (years)|
|silver fir-Douglas-fir||Abies amabilis-Pseudotsuga menziesii var. menziesii||>200|
|grand fir||Abies grandis||35-200 |
|maple-beech||Acer-Fagus spp.||684-1,385 [34,168]|
|silver maple-American elm||Acer saccharinum-Ulmus americana||<5 to 200|
|sugar maple||Acer saccharum||>1,000|
|sugar maple-basswood||Acer saccharum-Tilia americana||>1,000 |
|birch||Betula spp.||80-230 |
|California montane chaparral||Ceanothus and/or Arctostaphylos spp.||50-100 |
|sugarberry-America elm-green ash||Celtis laevigata-Ulmus americana-Fraxinus pennsylvanica||<35 to 200 |
|mountain-mahogany-Gambel oak scrub||Cercocarpus ledifolius-Quercus gambelii||<35 to <100 |
|Atlantic white-cedar||Chamaecyparis thyoides||35 to >200|
|beech-sugar maple||Fagus spp.-Acer saccharum||>1,000|
|black ash||Fraxinus nigra||<35 to 200 |
|green ash||Fraxinus pennsylvanica||<35 to >300 [52,168]|
|western juniper||Juniperus occidentalis||20-70|
|Rocky Mountain juniper||Juniperus scopulorum||<35 |
|cedar glades||Juniperus virginiana||3-22 [68,121]|
|tamarack||Larix laricina||35-200 |
|western larch||Larix occidentalis||25-350 [12,18,42]|
|yellow-poplar||Liriodendron tulipifera||<35 |
|Great Lakes spruce-fir||Picea-Abies spp.||35 to >200|
|northeastern spruce-fir||Picea-Abies spp.||35-200 |
|Engelmann spruce-subalpine fir||Picea engelmannii-Abies lasiocarpa||35 to >200 |
|black spruce||Picea mariana||35-200|
|conifer bog*||Picea mariana-Larix laricina||35-200 |
|blue spruce*||Picea pungens||35-200 |
|red spruce*||Picea rubens||35-200 |
|Rocky Mountain bristlecone pine||P. aristata||9-55 [45,46]|
|whitebark pine*||Pinus albicaulis||50-200 [1,9]|
|jack pine||Pinus banksiana||<35 to 200 [34,50]|
|Rocky Mountain lodgepole pine*||Pinus contorta var. latifolia||25-340 [17,18,161]|
|Sierra lodgepole pine*||Pinus contorta var. murrayana||35-200 |
|shortleaf pine||Pinus echinata||2-15|
|shortleaf pine-oak||Pinus echinata-Quercus spp.||<10 |
|Jeffrey pine||Pinus jeffreyi||5-30|
|western white pine*||Pinus monticola||50-200|
|Pacific ponderosa pine*||Pinus ponderosa var. ponderosa||1-47 |
|interior ponderosa pine*||Pinus ponderosa var. scopulorum||2-30 [11,16,101]|
|Arizona pine||Pinus ponderosa var. arizonica||2-15 [16,35,140]|
|red pine (Great Lakes region)||Pinus resinosa||3-18 (x=3-10) [33,58]|
|red-white pine* (Great Lakes region)||Pinus resinosa-P. strobus||3-200 [34,75,106]|
|pitch pine||Pinus rigida||6-25 [30,76]|
|eastern white pine||Pinus strobus||35-200|
|eastern white pine-eastern hemlock||Pinus strobus-Tsuga canadensis||35-200|
|eastern white pine-northern red oak-red maple||Pinus strobus-Quercus rubra-Acer rubrum||35-200|
|loblolly pine||Pinus taeda||3-8|
|loblolly-shortleaf pine||Pinus taeda-P. echinata||10 to <35|
|Virginia pine||Pinus virginiana||10 to <35|
|Virginia pine-oak||Pinus virginiana-Quercus spp.||10 to <35|
|sycamore-sweetgum-American elm||Platanus occidentalis-Liquidambar styraciflua-Ulmus americana||<35 to 200 |
|eastern cottonwood||Populus deltoides||<35 to 200 |
|aspen-birch||Populus tremuloides-Betula papyrifera||35-200 [50,168]|
|quaking aspen (west of the Great Plains)||Populus tremuloides||7-120 [11,66,110]|
|black cherry-sugar maple||Prunus serotina-Acer saccharum||>1,000 |
|mountain grasslands||Pseudoroegneria spicata||3-40 (x=10) [10,11]|
|Rocky Mountain Douglas-fir*||Pseudotsuga menziesii var. glauca||25-100 [11,13,14]|
|coastal Douglas-fir*||Pseudotsuga menziesii var. menziesii||40-240 [11,112,131]|
|California mixed evergreen||Pseudotsuga menziesii var. menziesii-Lithocarpus densiflorus-Arbutus menziesii||<35|
|California oakwoods||Quercus spp.||<35 |
|northeastern oak-pine||Quercus-Pinus spp.||10 to <35|
|white oak-black oak-northern red oak||Quercus alba-Q. velutina-Q. rubra||<35 |
|canyon live oak||Quercus chrysolepis||<35 to 200|
|blue oak-foothills pine||Quercus douglasii-P. sabiniana||<35 |
|northern pin oak||Quercus ellipsoidalis||<35 |
|Oregon white oak||Quercus garryana||<35 |
|bear oak||Quercus ilicifolia||<35 |
|California black oak||Quercus kelloggii||5-30 |
|bur oak||Quercus macrocarpa||<10 |
|oak savanna||Quercus macrocarpa/Andropogon gerardii-Schizachyrium scoparium||2-14 [121,168]|
|chestnut oak||Quercus prinus||3-8|
|northern red oak||Quercus rubra||10 to <35|
|post oak-blackjack oak||Quercus stellata-Q. marilandica||<10|
|black oak||Quercus velutina||<35 |
|redwood||Sequoia sempervirens||5-200 [11,56,158]|
|western redcedar-western hemlock||Thuja plicata-Tsuga heterophylla||>200 |
|eastern hemlock-yellow birch||Tsuga canadensis-Betula alleghaniensis||100-240 [160,168]|
|eastern hemlock-white pine||Tsuga canadensis-Pinus strobus||x=47 |
|western hemlock-Sitka spruce||Tsuga heterophylla-Picea sitchensis||>200|
|mountain hemlock*||Tsuga mertensiana||35 to >200 |
To the extent that woods strawberry plants can survive fire, or that seedlings can establish in the
postfire environment, it is apparent that fire can have a positive effect on woods strawberry populations. A
review by Patterson and others  indicated that it regenerates from stolons following fire, reaching
preburn levels within 3 to 7 years. Using the nomenclature of Volland and Dell , Powell  rated woods
strawberry postfire response as medium, suggesting it will regain its preburn frequency or cover in 5 to
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
While some studies indicate greater abundance of woods strawberry on burned versus unburned plots [113,118], other studies indicate an initial postfire decrease in woods strawberry abundance [104,159] and/or an increase in abundance 3 or more years after fire [2,117,154]. Still others report more equivocal results (e.g., [3,96]). Reported differences may be due to a number of factors, including differences in sampling protocols. For example, some studies compare paired burned and unburned plots at some time after fire, while others compare prefire abundance to postfire abundance over varying numbers of years. Additionally, some studies suggest a correlation between fire severity and woods strawberry response [19,20,82,143], while fire severity estimates are not consistently reported in other studies. It should also be noted that other factors besides fire severity may affect species-specific postfire response. Hypothetically, factors such as the character of the competing vegetation, herbivory, and additional disturbance such as flooding/debris flow may interact with the effects of fire. Interactions between such factors can confound interpretation of postfire data, leading to ambiguous results.
Two studies demonstrate greater woods strawberry presence on burned sites, compared with adjacent unburned habitat. Ten to 11 years after a 1945 wildfire in the Oregon Coast Range, frequency of woods strawberry in burned quadrats was 9%, while none was sampled in unburned forest. The unburned forest was estimated at around 300 years old, composed mainly of Douglas-fir succeeding to western hemlock. Burn characteristics were not well described, although it was apparently a predominantly stand-replacing fire . Similarly, woods strawberry was most prevalent (7% cover; 40% frequency) in a 4-year-old burned stand compared to mature (230 to 320 years old) and second-growth (53 to 80 years old) stands in Douglas-fir-western hemlock/Pacific rhododendron (Rhododendron macrophyllum) communities on the Olympic Peninsula, Washington. Although no details were provided about burn conditions, vegetation data indicate that it was a stand-replacing fire in what was previously mature forest. Woods strawberry was not present in any of the 13 sampled stands of mature forest. It was present but sparse (<1% cover and frequency) in 3 second-growth stands. It was not clear what type of disturbance initiated the second-growth stands .
Other studies show a reduction in woods strawberry in burned plots compared with unburned plots in early postfire years. Three years after the 1979 Ship Island Burn in the Middle Fork Salmon River drainage, central Idaho, woods strawberry cover was significantly (P<0.05) lower in burned plots compared with paired unburned plots . Leege and Godbolt  studied herbaceous response to prescribed burning and grass-seeding treatments to improve elk winter range in shrub-dominated habitat in north-central Idaho. Prescribed burning was conducted in mid-May, and all vegetation sampling took place in July or August. General burn conditions are provided in , but information concerning fire behavior or severity was not. Their data show woods strawberry was less frequent on burned plots than unburned plots.
|Woods strawberry frequency of occurrence within each of ten 2-foot (61 cm) diameter circular measurement plots, 1 year prior to burning and 1, 2, and 4 years after burning (adapted from )|
Woods strawberry populations in postfire plots in these 2 studies may still have been recovering. It is unknown whether woods strawberry frequency increased on these sites in subsequent years.
Some studies indicate that populations of woods strawberry generally remain relatively low in the early postfire environment and begin increasing after 2 or more years [2,117,154]. These studies do not, however, provide information on abundance of woods strawberry before fire or in paired unburned plots. Following the Little Sioux Wildfire in northeastern Minnesota in 1971, vegetation data were collected from seventy 0.605 m² plots each August for 5 years. No other information about the fire was provided .
|Total number of woods strawberry plants sampled each August after a 1971 wildfire in northeastern Minnesota |
Ahlgren  suggested that in forests of the north-central United States and adjacent central Canada, woods strawberry increases gradually for several years following fire, peaking during the 5- to 10-year postfire period, and subsequently declining.
|Average percent cover of woods strawberry in “burned-over jack pine (Pinus banksiana)-black spruce (Picea mariana) forests in northeastern Minnesota at different intervals after fire" (adapted from )|
|Years after fire||1||2||3||4||5||10||15||20||30||50||80|
|Average percent cover (%)||1||2||2||3||4||5||1||1||1||1||1|
Twenty years of woods strawberry cover data were collected each July following the Plant Creek wildfire that burned in late August 1972 in the Sapphire Range, western Montana. These data indicate that woods strawberry was absent for 3 to 17 years following the fire, but eventually established in 9 of 10 study areas. Woods strawberry cover never exceeded 5% on any study area during this time. Prefire data were not provided, so it is not known if these populations were of sprout or seed origin .
|Number of postfire study areas (out of 10 total) containing woods strawberry (adapted from ).|
|Number of study areas||0||0||0||2||2||3||2||4||4||4||4||6||3||5||6||5||5||6||8||7|
Another study showed conflicting results. Postfire response of woods strawberry differed between 2 northern Minnesota mixed conifer-hardwood forest sites. One site was a 10-year-old jack pine plantation burned by wildfire in a late April 1952, and the other site was dominated by jack pine and black spruce and burned by wildfire in July 1955. An unburned mixed conifer-hardwood site, dominated by black spruce, jack pine, and paper birch, served as a contol. Little information about fire behavior or burn conditions was provided, although the authors noted that "little or no soil burn occurred" .
|Woods strawberry percent frequency within thirty 10 m² plots on each site (adapted from )|
|Mixed conifer-hardwood (unburned)||Jack pine (years after burn)||Jack pine-black spruce (years after burn)|
|1956||1965||1954 (3)||1956 (5)||1965 (14)||1956 (2)||1959 (5)||1965 (11)|
Fire severity, particularly fire residence time and magnitude of the downward heat pulse associated with the fire, is likely to impact woods strawberry survival and postfire response. Greater fire severity is associated with increased duff consumption, greater soil heating, and consequently, reduced woods strawberry survival. For example, Hooker and Tisdale  indicated that woods strawberry increased following "low intensity" prescribed fire in a northern Idaho shrubland, but did not "benefit" from "more intense" fire. On shelterwood cutting units in a northern Idaho mixed conifer forest, woods strawberry postfire year 1 cover was slightly lower on a site burned under dry fuel conditions than on a site burned under moist fuel conditions. Differences in fuel moisture between treatments were primarily attributable to duff moisture levels (88% for the moist treatment; 41% for the dry treatment). Average duff consumption was 30% for the moist burn, compared with 90% for the dry burn, indicating higher fire severity on the dry burn site. More detailed burn conditions and fire behavior information are available in .
|Woods strawberry cover during summer just prior to treatment and 1 year after burning (adapted from )|
Following prescribed fires in western Wyoming quaking aspen (Populus tremuloides) communities, woods strawberry biomass decreased with increasing severity 3 years after fire. This pattern was less consistent in postfire year 12 [19,20].
|Woods strawberry production before, 3 years after, and 12 years after fires of varied severitya (adapted from [19,20]). Prefire production was 108 kg/ha.|
|Years after fire||3||12|
|Light||94 kg/ha||75 kg/ha|
|Moderate||78 kg/ha||14 kg/ha|
|Heavy||51 kg/ha||45 kg/ha|
a Light burns indicate an estimated 0% to 20% of litter and duff consumed
Moderate burns indicate an estimated 20% to 80% of litter and duff consumed
Heavy burns indicate an estimated 81% to 100% of litter and duff consumed
Further evidence linking fire severity with woods strawberry's postfire response is provided by Wang and Kimball , who examined vegetation response following a wildfire in a boreal mixedwood forest codominated by quaking aspen and a mixture of balsam fir (Abies balsamea), white spruce (Picea glauca), black spruce and/or jack pine.
|Average woods strawberry cover and frequency over 4 postfire years |
aScorched indicates litter not burned or partially burned
bLightly burned indicates litter burned but with little to no duff consumption
cSeverely burned indicates forest floor completely consumed; organic matter in upper mineral soil horizon may also be partially consumed
Two northern Minnesota studies also indicate a stronger woods strawberry postfire response when fire is less severe. At 2 jack pine forest sites that were logged and then burned 1 year later, frequency of woods strawberry was similar before cutting and burning (80-83%) but differed between sites after treatment. Differences in fire severity might explain lower frequency of woods strawberry at the Grass Lake site (3-13%, 1-2 years after fire) compared with the East Bearskin Lake site (57-83%, 1-2 years after fire). Temperatures reached at the soil surface were, on average, greater than 900° F (480° C) at the Grass Lake site and less than that at the East Bearskin Lake site . In another northern Minnesota study conducted in several forest types, woods strawberry frequency tended to be higher on burned versus unburned plots, although frequency was lower on a severe burn versus a burn of moderate severity at one site . Lack of prefire information and mixed sampling approaches among sites make results from this study difficult to interpret.
On ponderosa pine and Douglas-fir communities in the Blue Mountains of northeastern Oregon, woods strawberry cover and frequency were higher on unburned control sites than on prescribed burned, thinned, or thinned-and-burned sites. Woods strawberry was determined to be an indicator species for unburned sites (P≤0.05). For further information on the effects of thinning and burning treatments on woods strawberry and 48 other species, see the Research Project Summary of Youngblood and others'  study.
These fire studies also provide information on postfire responses of plant species in communities that include woods strawberry:
It has been suggested that woods strawberry might be an important species for mitigating postfire erosion potential. From observations of postfire shrubfields in northern Idaho, Hooker and Tisdale  wrote that woods strawberry "appeared to have an important stabilizing influence on the surface soils of the steeper slopes, since it was abundant after burning and sent out numerous stolons."
Tame mule deer utilized woods strawberry in Utah and Colorado. In a lodgepole pine-dominated forest area in northeastern Utah, woods strawberry constituted 5% by weight of the summer diet of tame mule deer in clearcut forest and mature forest habitats . Tame mule deer utilized small amounts of woods strawberry in lodgepole pine and Englemann spruce (Picea engelmannii)-subalpine fir (Abies lasiocarpa) habitats in central Colorado in summer . In an experiment on a central Colorado ponderosa pine/bunchgrass range, observations of grazing preferences of tame mule deer indicated that woods strawberry was among preferred food species. Average percent of mule deer diet comprised of woods strawberry was as follows :
|Average monthly use||April||May||June||July||August||October|
Woods strawberry is also eaten by other native mammals, including grizzly bears , black bears [150,151], and raccoons , although it is unclear if these animals are eating strictly fruit, or if they are also utilizing foliage.
Fruits are eaten by grouse and songbirds [83,150,151]. Wild strawberry is "perhaps the most important herbaceous food plant for" ruffed grouse in Minnesota . Hungerford  suggested that it was an important food for ruffed grouse in Idaho.
Palatability/nutritional value: According to Steele and Geier-Hayes [150,151] woods strawberry is moderately palatable to deer, elk and sheep. Its leaves remain "green through the winter" and provide a higher forage value "than most herb layer species during that season."
Cover value: No information is available on this topic.VALUE FOR REHABILITATION OF DISTURBED SITES:
OTHER MANAGEMENT CONSIDERATIONS:
Published information provides conflicting evidence concerning woods strawberry grazing tolerance. Hall  reported that wild strawberries tended to increase with overgrazing in the Blue Mountains of eastern Oregon and southeastern Washington. Steele and Geier-Hayes [147,148,149] indicated that, on "cutover" sites in grand fir- and Douglas-fir-dominated habitat types in Idaho, woods strawberry was less tolerant of heavy grazing than either Virginia strawberry or other common grazing-tolerant forbs. It was also suggested that woods strawberry is susceptible to trampling from heavy livestock traffic [147,148,149]. In northern California, Saenz  recorded the presence of woods strawberry in "lightly" grazed (only grazed "late in the season" by cattle) Oregon white oak woodland, but it was not observed in "heavily" grazed (grazed by cattle "for as much of the year as weather permitted") woodland, nor in "lightly" grazed or "heavily" grazed grassland.
In meadow habitat surrounded by ponderosa pine (Pinus ponderosa) forest on the Mogollon Rim, northern Arizona, exclusion of grazing by cattle, elk and deer had no consistent effect on relative abundance of woods strawberry. Comparisons were made between grazed plots and fenced exclosure plots where there had been no grazing for 8 to 9 years. Woods strawberry "relative abundance (%)" ranged from 0 to 6.5%, with no discernable effect of grazing among 3 sites.
A study on the Rogue River National Forest, Oregon, suggests that on logged sites where woods strawberry is present, removing slash (in this case piling and burning) results in greater woods strawberry presence, compared with leaving slash in place .Limited evidence suggests that woods strawberry may be relatively resistant to some herbicides. Rice and Toney  studied the effects of herbicide treatments for controlling spotted knapweed (Centaurea maculosa) on native forest and grassland vegetation in west-central Montana. At a single site, woods strawberry occurrence was not significantly (P=0.67) different in untreated plots and plots treated once with either picloram or clopyralid . It also does not appear particularly susceptible to glyphosate . Caution should be observed when making assumptions about effects of specific herbicides, application rates, and repeated applications on woods strawberry.
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