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SPECIES: Kalmia latifolia
|Annette Hoeggemeier, Botanical Garden Bochum, Germany|
AUTHORSHIP AND CITATION:
League, Kevin R. 2005. Kalmia latifolia. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://www.fs.fed.us/database/feis/plants/shrub/kallat/all.html . FEIS ABBREVIATION:
Kalmia latifolia L. var. laevipes Fernald 
NRCS PLANT CODE [ 113]:
The scientific name of mountain laurel is Kalmia latifolia L. (Ericaceae) [12,21,40,42,62,94,108,134,135].
FEDERAL LEGAL STATUS:
|New York||Exploitably Vulnerable |
Mountain laurel is found in openings or open stands of spruce-fir (Picea-Abies spp.) forests in the central and southern Appalachian arboreal highlands, mountain tops, and "balds" (see below) . These types of forest are dominated by red spruce (P. rubens) but may coalesce with mixed hardwood or northern hardwood forests on lower slopes. Common overstory associates include Fraser fir (A. fraseri), yellow buckeye (Aesculus flava), sweet birch (Betula lenta), and black cherry (Prunus serotina) [38,41]. Common understory associates include rhododendrons (Rhododendron spp), American mountain-ash (Sorbus americana), and possumhaw (Viburnum nudum var. cassinoides) [2,66,111]. Other understory associates include highbush cranberry (V. edule), mountain holly (Ilex montana), speckled alder (Alnus rugosa), pin cherry (P. pensylvanica), serviceberry (Amelanchier spp.), raspberries (Rubus spp.), blueberries (Vaccinium spp.), and huckleberries (Gaylussacia spp.) [100,128]. In closed red spruce stands, mosses, lichens, and clubmosses (Lycopodium spp.) dominate the understory along with other shade tolerant species such as wood sorrel (Oxalis spp.), trillium (Trillium spp.), and wintergreen (Gaultheria procumbens) .
Heath "balds" that form along the tops of the highest (>4000 feet (1200 m)) southern and central Appalachian mountain peaks are dominated by dense thickets of ericaceous shrubs. Mountain laurel is a dominate species of these habitats or may co-dominate with Catawba rosebay (Rhododendron catawbiense) at subxeric/submesic ecotones [16,128]. However, a considerable difference in the distribution of these 2 species is present over an elevational gradient. Mountain laurel tends to favor the lower elevation balds whereas above 6000 feet (1800 m), where the highest balds exist, Catawba rosebay is common [4,5,9,17]. Common shrub associates include Catawba rosebay, black chokeberry (Photinia melanocarpa), mountain sweetpepperbush (Clethra acuminata), highbush blueberry (Vaccinium corymbosum), mountain holly, possumhaw, blackberries, and American mountain-ash. Herbaceous abundance is limited by these dense thickets [44,100,127].
Mountain laurel is a common understory component of northern hardwood forests. These forests are generally found at middle to high elevations in the central and northern Appalachian Mountains, often transitioning to spruce/fir or mixed hardwood forest at higher or lower elevations, respectively [103,111,128]. Common overstory tree species include sugar maple (Acer saccharum), basswood (Tilia americana), yellow birch (B. alleghaniensis), black cherry, red spruce, white spruce (Picea glauca), American beech (Fagus grandifolia), eastern white pine (Pinus strobus), eastern hemlock (Tsuga canadensis), northern red oak (Quercus rubra), white oak (Q. alba), and yellow-poplar (Liriodendron tulipifera) [100,103]. Understory associates include beaked hazel (Corylus cornuta), eastern leatherwood (Dirca palustris), red elderberry (Sambucus racemosa var. racemosa), alternate-leaf dogwood (Cornus alternifolia), bush-honeysuckle (Diervilla lonicera), Canada yew (Taxus canadensis), red raspberry (Rubus idaeus), and blackberries. Carolina springbeauty (Claytonia caroliniana), snow trillium (Trillium grandiflorum), anemone (Anemone spp.) marsh blue violet (Viola cucullata), downy yellow violet (V. pubescens), hairy Solomon's seal (Polygonatum pubescens), starry Solomon's-seal (Maianthemum stellatum), hairy sweet-cicely (Osmorhiza claytonii), adderstongue (Ophioglossum spp.), Jack-in-the pulpit (Arisaema triphyllum), bigleaf aster (Eurybia macrophylla), and clubmosses [103,127].
Mountain laurel is an understory species associated with mixed hardwood forest. This habitat occurs on rich, mesic sites, on sandy plains, rock outcrops, and at the outer edges of floodplains east of the Mississippi. These forests often support a high level of plant diversity [89,107,111]. Overstory associates of mountain laurel are numerous and include northern red oak, white oak, black oak (Q. velutina), scarlet oak (Q. coccinea), southern red oak (Q. falcata), post oak (Q. stellata), yellow-poplar, eastern white pine, American beech, sugar maple, red maple (Acer rubrum), black cherry, American basswood, sweetgum (Liquidambar styraciflua), white ash (Fraxinus americana), green ash (F. pennsylvanica), aspen (Populus tremuloides), hickories (Carya spp.), black tupelo (Nyssa sylvatica), black walnut (Juglans nigra), jack pine (Pinus banksiana), eastern hemlock , and elm (Ulmus spp.) [12,79,128]. Common mid-canopy tree associates include flowering dogwood (Cornus florida), holly (Ilex spp.), eastern hophornbeam (Ostrya virginiana), sassafras (Sassafras albidum), American bladdernut (Staphylea trifolia), eastern redbud (Cercis canadensis), common persimmon (Diospyros virginiana), and serviceberry. Common understory shrubs and vines include greenbrier (Smilax spp.), blueberries, rosebay rhododendron (Rhododendron maximum), eastern leatherwood, witch-hazel (Hamamelis virginiana), beaked hazel, spicebush (Lindera benzoin), poison-ivy (Toxicodendron radicans), and grape (Vitis spp.) [6,100].
Mountain laurel is the primary understory species of xeric pine (Pinus spp.) -hardwood forest. This forest type is common on southerly facing slopes in the southern and central Appalachians, adjacent foothills, piedmont, and coastal plains. These forests are thought to be highly dependent on moderate- to high-intensity fires . However fire suppression, drought-induced insect infestations, and logging have promoted the dominance of hardwood species and dense thickets of mountain laurel in later-successional stands [110,111]. Early-successional stands are dominated by pitch pine (P. rigida), Table Mountain pine (P. pungens), and/or Virginia pine (P. virginiana) [10,29]. As stands mature, other associated tree species arrive  and include chestnut oak (Q. prinus) [27,28], white oak, bear oak (Q. ilicifolia), blackjack oak (Q. marilandica), chinkapin oak (Q. muehlenbergii), post oak, black oak, shortleaf pine (P. echinata), scarlet oak, red maple, black tupelo, sourwood (Oxydendrum arboreum), American chestnut (Castanea dentata), black locust (Robinia pseudoacacia), hickories, and sassafras [14,86,93,107]. Associated shrub species include downy serviceberry (Amelanchier arborea), coastal sweetpepperbush (Clethra alnifolia), black huckleberry (G. baccata), dwarf huckleberry (G. dumosa), blue huckleberry (G. frondosa), sheep laurel (Kalmia angustifolia), wintergreen, fetterbush (Leucothoe racemosa), maleberry (Lyonia ligustrina), piedmont staggerbush (L. mariana), bayberry (Morella spp.), black chokecherry, black cherry, flameleaf sumac (Rhus copallinum), cat greenbrier (Smilax glauca), roundleaf greenbrier (S. rotundifolia), Virginia tephrosia (Tephrosia virginiana), low sweet blueberry (Vaccinium angustifolium), and hillside blueberry (V. pallidum) [5,17,57,130].
Mountain laurel is a common understory species of oak (Quercus spp.)-hickory forests in the southern and east-central United States. Oak-hickory forests are found on sand deposits and on dry upper slopes, ravines, and ridges of southerly or westerly aspects . This type of forest covers approximately 127 million acres (51 million ha) or 34% of the forests in the eastern U.S. Oak-hickory forest dominates the east-central U.S. but gives way to mixed hardwoods to the north and in the higher terrain of the Appalachian Mountains, and to pine-hardwood forest to the south . Dominant overstory associates include blackjack oak, post oak, northern red oak, white oak, black oak, scarlet oak, southern red oak, and turkey oak (Q. laevis). Other overstory associates include pignut hickory (C. glabra), black hickory, mockernut hickory (C. tomentosa), shingle oak (Q. imbricaria), winged elm (U. alata), black tupelo, and sourwood [12,111,128]. Understory tree and shrub associates include flowering dogwood, blueberries, huckleberries, and sumac (Rhus spp.). Herbaceous plant associates include bluestems (Andropogon spp.), little bluestem (Schizachyrium scoparium), and various sedges (Carex spp.) [14,100].
Mountain laurel is an understory associate of eastern white pine forests. These forests occur on a variety of sites along a moisture gradient from wet bogs and moist stream bottoms to xeric sand plains and rocky ridges. Eastern white pine often forms pure stands but more frequently occurs as a codominant or associate of northern hardwood or mixed hardwood forest types containing northern red oak and/or red maple . In the northern range of this species through Maine and New Brunswick, eastern white pine forests occur on mesic sites along or near bogs. In the southern and central Appalachian Mountains, pure stands mainly occur on northerly aspects, in coves, and on stream bottoms . Due to the large amount of shade in the understory of these forests, herbaceous and shrub species are scarce in pure stands of eastern white pine. On dry sites where stand densities may allow more light, mountain laurel's understory associates include blueberry, wintergreen, bush-honeysuckle, sweet fern (Comptonia peregrina), western bracken fern (Pteridium aquilinum), clubmoss, and broomsedge bluestem (A. virginicus) [6,26]. On moist rich sites, associates include mountain woodsorrel (Oxalis montana), partridgeberry (Mitchella repens), wild sarsaparilla (Aralia nudicaulis), Jack-in-the-pulpit, and eastern hayscented fern (Dennstaedtia punctilobula). Herbaceous associates include bigleaf aster, wild lily-of-the-valley (Maianthemum canadense), and bunchberry (Cornus canadensis) [103,125].
Mountain laurel commonly occurs in the understory of oak-pine forest. These forests are found along the Atlantic and Gulf coastal plains, piedmont, and floodplains. Pines may make up 25% to 50% of the composition of these forests . Common overstory associates include shortleaf pine, loblolly pine (P. taeda), scarlet oak, southern red oak, water oak (Q. nigra), willow oak (Q. phellos), black tupelo, sweetgum, Table Mountain pine, mockernut and pignut hickories, winged elm, sourwood, red maple, American beech, and Carolina ash (F. caroliniana). Common understory woody species include flowering dogwood, redbud, and common persimmon [20,91,100,110,111].
Mountain laurel frequently occurs in "pine barren or plain" communities of the New Jersey and New York coastal plains . These habitats have a limited distribution of fire-dependent habitats ranging from pine forests to dwarfed (< 10 feet (3.0 m) tall) shrubland communities . Dominant overstory species include pitch pine and other tree species such as blackjack oak, bear oak, shortleaf pine, and dwarf chinquapin oak (Q. prinoides). Shrub associates include black huckleberry, hillside blueberry, dangleberry (Gaylussacia frondosa), piedmont staggerbush, and highbush blueberry [20,43,57,78,129].
Mountain laurel is an occasional understory species in upland and mesic sites within longleaf pine (P. palustris) forests and savannas. The fire dependent forests dominated by longleaf pine are located in and along the Atlantic and Gulf coastal plains and lower Piedmont regions of Georgia and Alabama . Associated species on mesic coastal plain sites include southern red oak, blackjack oak, water oak, flowering dogwood, black tupelo, sweetgum, persimmon, and sassafras. Associated species on xeric sandhill sites include turkey oak, bluejack oak (Q. incana), and live oak (Q. virginiana). Associated shrubs include inkberry (I. glabra), yaupon (I. vomitoria), large gallberry (I. coriacea), southern bayberry (Myrica cerifera), blueberries, huckleberries, blackberries, saw-palmetto (Serenoa repens), sweetbay (Magnolia virginiana), cyrilla (Cyrilla racemiflora), and buckwheat tree (Cliftonia monophylla). In longleaf pine's western range, groundcover includes bluestems and panicums (Panicum spp.). In its eastern range, pineland threeawn (Aristida stricta) is the primary groundcover [20,92,100].
Classifications describing plant communities in which mountain laurel is a dominant species are as follows:North Carolina [11,16,82,100]
J.S. Peterson @ USDA-NRCS PLANTS Database
GENERAL BOTANICAL CHARACTERISTICS:
This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g. [12,21,40,42,62,94,108,134,135]).
Mountain laurel is a native North American perennial shrub . Mature plants
are 6.5 to 10 feet (2-3 m) tall, but may reach up to 40 feet (12 m) in height.
Leaves are evergreen, sclerophyllous, leathery, 0.75 to 4 inches (2-10 cm) long,
and 1 to 2 inches (2.5-5 cm) wide [12,21,40]. The inflorescence is a compound corymb
of showy saucer shaped flowers, 0.5 to 1 inch (1.5-3 cm) wide. Stems are long and narrow
with furrows and ridges, often sloughing in narrow strips or flakes [62,134]. The
fruit is a capsule, 4-6 mm in diameter, bearing hundreds of small (< 1 mm in length,
< 0.5 mm wide) seeds [42,94,135]. Below a basal burl, mountain laurel has a thick
rootstock that supports numerous other vertical and horizontal roots that may reach up
to 30 inches (76 cm) in depth . Mountain laurel roots associate with
mycorrhizal fungus [60,68].
RAUNKIAER  LIFE FORM:
Mountain laurel regenerates from seed or asexually by sprouting, suckering, and layering [68,70,95,99,132].
Breeding system: Mountain laurel is monoecious 
Pollination: is insect or self-mediated [62,118]. Bumblebees are the primary species of insect-mediated pollination . Mountain laurel anthers are positioned under tension which is suddenly released when a bumblebee or other insect lands on the flower. If the flowers remain unpollinated, the anther will self release pollen onto the flower's own pistil [12,68,71]. Real and Rathcke  found that insect flower visitation depends on annual nectar production rates, which vary from year to year.
Seed production: Seeds are contained in small fruit-like capsules each containing 300 to 700 seeds. Individual mountain laurel shrubs can produce 1000s of seeds annually [68,95].
Seed dispersal: Mountain laurel seeds are wind dispersed and rarely travel beyond 50 feet (15 m) from the parent plant. Seedfall begins in the fall and continues through the spring [68,95].
Seed banking: Mountain laurel seed remains viable in the soil for several years [59,68]. Jaynes  found that an average of 71% of seed 2 to 4 years old remained viable, whereas viability declined to 20% after 8 years.
Germination: Mountain laurel germination is enhanced by stratification [59,68]. Jaynes  found that 66% of mountain laurel seed germinated after being refrigerated at 39 °F (4 °C) for 8 weeks versus 19% of untreated controls. Treatments using a gibberellin solution also enhanced germination. Kurmes  found that germination of mountain laurel seed is more successful when soil temperatures are 64 to 71.5 °F (18 to 22 °C).
Seedling establishment/growth: Mountain laurel requires a moss-covered or moist mineral soil seedbed for successful establishment [68,99]. Seedlings are moderately shade tolerant but tend to grow more vigorously in forest openings [68,75]. Growth rates of mountain laurel are relatively slow; young plants (< 15 years) add about 5 inches (12 cm) in height and 3.5 inches (9 cm) in crown width annually [68,84]. Older mountain laurel stems may attain heights up to 40 feet (12 m) and diameter at ground level of 5 inches (15 cm) . Mountain laurel is usually a tall, spreading shrub throughout most of its range, yet in the fertile Blue Ridge valleys and in the Allegheny Mountains of the southern Appalachian Mountains mountain laurel may attain the size of a small tree. In 1877, botanist Asa Gray noted at Caesar's Head in extreme northwest South Carolina that the trunks of mountain laurel reached 50 inches (125 cm) in circumference. Mountain laurel burl size varies with age. A 600-pound (272 kg) burl has been reported in western North Carolina . In the southern Appalachian Mountains, mountain laurel stem density can range from sparse to nil on mesic sites to thickets of over 26,000 stems/ha on xeric southerly slopes. Basal area of mountain laurel at 1 inch (2.5 cm) above ground level can exceed 25 m2/ha .
Mountain laurel's primary mode of reproduction is through sprouting from basal burls,
layering, or suckering [68,70,99,132].
Soil: Mountain laurel occurs commonly on xeric sites with rocky or sandy acidic soils on southern-facing slopes, ridges, and mountain hillsides [8,40,75,81,94,108,134], although it occasionally occurs on well-drained mesic floodplain soils . Mountain laurel may be less abundant or entirely absent on northerly-facing mesic slopes or along stream bottoms . Mountain laurel forms dense, almost impenetrable patches known locally as "laurel hells" or "ivy thickets," on upper slopes and ridges where tree canopy may be sparse or lacking [60,84]. These sites are characterized by steep rocky slopes, high solar radiation, and acidic sandy soils containing low amounts of organic matter [36,84,94,108,134]. In the southern Appalachian Mountains mountain laurel occurs more frequently on sites with a thin A soil horizon layer . Where mountain laurel is common, soil nutrient levels and water availability are generally low [64,82]. The following table shows average soil chemical and physical properties from a southern Appalachian xeric oak-pine forest .
|N (%)||C (%)||pH||Ortho-p (mg kg-1)||Ca (mg kg-1)||K (mg kg-1)||Mg (mg kg-1)||Bulk density (g cm-3)|
Mountain laurel foliage litterfall contributes nutrients back to forest soil . The following table shows estimated average mountain laurel foliage nutrient concentration percent.
|Lignin (%)||Ca (%)||Mg (%)||P (%)||K (%)|
Mountain laurel is dependent on mycorrhizal fungus associated with its root system in the soil, which ensures adequate absorption of water and minerals even in areas of nutrient-poor, acidic soil .
Climate: Considerable climatic diversity is found throughout mountain laurel's range. In general, temperature, precipitation, and length of growing season increase from north to south. However, a wide variety of local microclimatic conditions exist in the complex topography of the Appalachian Mountain region. Habitats that include mountain laurel endure climate ranging from subtropical along coastal plains to temperate further inland. Seasonal weather patterns are driven by alternating cold/dry continental air masses from Canada and warm/moist air from the Gulf of Mexico. Precipitation is generally distributed uniformly throughout the year mostly as rain, while snow and ice are common in the winter months, especially in mountain laurel's northern range and higher mountainous terrain. Mean annual precipitation ranges from 39 to 78 inches (1000-2000 mm). Depending on location, annual snow accumulations range from 8 to 48 inches (200-1220 mm). Tropical cyclones are possible throughout the summer and fall months and can result in very high amounts of precipitation and wind [20,44,103,105].
Annual average precipitation for select locations are:
|State||Location||Mean Annual Precipitation||Citation|
|NC||Coweeta||71.3 inches (1810 mm)|||
|KY||Stanton||44.5 inches (1130 mm)|||
|TN||Cleveland||53.2 inches (1350 mm)|||
Seasonal variations in temperature increase away from the coast. Average winter
temperatures vary from 10 °F (-12 °C) in the north to 64 °F (18 °C) in mountain laurel's
southern range. Average summer temperatures are less variable, ranging from 70 to 72 °F
(21 to 22 °C) [20,44,103].
Stand scale disturbances: In the southern Appalachians and in other hardwood forests of the eastern U.S., mountain laurel quickly establishes after disturbance, sprouting aggressively from basal burls . Mountain laurel also re-establishes by suckering and layering after disturbance. Mountain laurel is shade-tolerant and is typically found in the understory of fast-growing, early-successional pioneer tree species such as yellow-poplar, black locust, and red maple [33,94]. As postdisturbance stands mature and senesce, mountain laurel commonly remains a dominant understory species . This is especially true in xeric communities such as pine-hardwood forest of the southern Appalachians where mountain laurel often persists from early to late stages of succession . For example, Elliot and others  found mountain laurel stem densities increased beyond precut densities during a 19-year period after a xeric pine-hardwood forests was clear-cut. Years before and after cutting and percent basal area of mountain laurel is as follows:
|Pre-cut||Years after cutting|
Gap scale disturbances: While large-scale canopy disturbances from regional drought, fire, and ice storms do occur periodically, small-scale openings in the canopy are much more common. These disturbances often come in the form of a "canopy gap" created by the loss of 1 or more overstory individuals by any number of factors (i.e. wind throw, lightning, disease, insect, etc.) . Canopy openings provide increased light and temperature to the forest surface, stimulating establishment of new mountain laurel shrubs at a disturbed site .
Synergistic relationships with overstory canopy: In the southern Appalachians mountain laurel has grown abundant in areas where insect outbreaks are responsible for mortality of overstory species. In xeric pine-hardwood or oak-pine forests, drought-induced southern pine beetle attacks are responsible for reducing densities of overstory tree species and increasing densities of mountain laurel. In these stands successful regeneration of overstory species is much less than in stands with less mountain laurel . In fact mountain laurel is hypothesized as the most important competitor to regenerating hardwood and some pine species. Dense thickets of mountain laurel form a barrier to juvenile trees, suppressing growth and limiting establishment and survival. Mountain laurel's influence on overstory growth is lessened once juvenile trees emerge from mountain laurel's canopy cover [22,34,63,85].
Some studies have found dissimilar results that indicate mountain laurel's influence on overstory regeneration might be less than previously thought. In northern hardwood and xeric pine-hardwood forests of New England, Kittredge and Ashton  found that a dense understory of mountain laurel negatively influenced only overstory pine species abundance, while overstory hardwood species abundance remained uninhibited. In the southern Appalachians, Waterman and others  found that the manual removal of mountain laurel from a pine-hardwood stand did not influence recruitment and establishment rates of juvenile trees. Clinton and others  found that the leaf surface area of mountain laurel is less than that of other understory shrubs, allowing considerable amounts of light to reach the forest floor for establishment of overstory species beneath its canopy.
Increased abundance over the past century: Increases in mountain laurel density across the Appalachian Mountains over the past century may be due to loss of the once regionally dominant American chestnut. This species was decimated by the chestnut blight of the early 20th century. Canopy gaps provided by decadent chestnut overstory have allowed higher amounts of light to reach the subcanopy and have contributed to increased abundance of mountain laurel and other ericaceous shrubs over the past century [13,35]. Also, the introduced gypsy moth has played a large role in shaping current forest structure over the past century. Researchers in the central Appalachians using remote sensing found that mountain laurel occurrence was strongly related to increased subcanopy light caused by gypsy moth defoliation . Other forest disturbances such as logging and fire suppression have also contributed to the increase in mountain laurel (see: Fire Regime) .
Water and Light: Mountain laurel is drought resistant and is a strong competitor for water resources at xeric sites [25,72,84]. Mountain laurel adapts to a broad range of light regimes, from moderate shade in forest understory to no shade in open or recently disturbed stands. Al-Hamdani and others  found that mountain laurel foliage chlorophyll a:b ratio was lower than that of other understory species. The authors considered this characteristic an adaptation of mountain laurel to low light availability.
In the absence of disturbance: Generally as juvenile stands mature, overstory canopy structure becomes more dense and mountain laurel densities decline due to less light reaching the forest floor. Hemond and others  found, in mixed hardwood forests of Connecticut, that mountain laurel stem density declined 50% in maturing forests over a 20-year period. Harrod and others  found similar declines of mountain laurel in maturing xeric pine-hardwood stands in the southern Appalachians.
Nutrient flux: In southern Appalachian forests, mountain laurel has as a
large influence on nutrient flux in forest soils. Elliot and others  found
in soils where mountain laurel is abundant, the contribution of their low-nutrient
leaves to litterfall can reduce litter quality, alter pH, decrease forest floor
decomposition rates, and alter overall soil quality.
Mountain laurel stem growth occurs during the spring and ceases during summer. Flowers bloom April to June from buds that form during the previous growing season. Flowers are numerous and may number in the 1,000s, especially from individuals that grow in open stands. Seed matures from September to October . The majority of mountain laurel leaves survive for 2 to 3 years. Mountain laurel leaves begin to die in the late spring during their 2nd growing season while a few persist into the 3rd; hence, about half of the leaves on any given plant are the current year's production. Leaf fall occurs throughout the year with peak litter production occurring in the autumn and spring. Annual leaf litter production is 127 kg per ha or 47% of its standing crop of leaves . Mountain laurel leaf moisture content peaks during late summer and is lowest during the spring .
Fire regime: : Many scientists believe that before the colonization of eastern forests by European settlers, forest fires were a major contributor to the stand dynamics of presettlement forests. The ignition sources of these fires include Native Americans and lightning . Frequent burning is hypothesized as one of the most important elements of the disturbance regime in some eastern forests, particularly in the xeric pine/hardwood forest-types that are primarily composed of pine and oak species with an understory of mountain laurel . These stands are thought to be highly dependent on frequent, high-intensity fires for their maintenance and rejuvenation. Mountain laurel presettlement abundance may be a critical component of pine forest structure as a ladder fuel, allowing fire to move from the surface to the crowns of serotinous pine species [112,120]. Fire suppression practices of the 19th and 20th centuries have diminished aboriginal-and lightning-ignited fires in these stands. In addition, drought-related insect infestations and previous logging practices have led to decreased densities of pines and increased densities of shade-tolerant overstory and understory species, including mountain laurel. In these stands mountain laurel is thought to be a major reproductive competitor with juvenile trees (See Successional Status), so its removal from the understory in some forests is currently a major objective of fire management (See Fire Effects) [36,86,112,117,124].
In oak forests with a mountain laurel dominated understory, infrequent (>25 years) low-severity surface fires in leaf litter were once a common element of the presettlement fire regime . A few of these forests, especially in ecotonal areas with table mountain and pitch pine, are believed to have endured infrequent stand replacement fires during periods of severe fire weather conditions [22,115,124]. However, fire suppression efforts have reduced the fire frequency in these forest types. The absence of fire in these forests may be as the primary reason for the decrease in abundance of oak forests and increase in abundance of mountain laurel and other shade-tolerant species over the past century across the eastern U.S. .
In Tennessee's Great Smoky Mountains National Park, Harmon , using fire scar data in a xeric pine-hardwood stand with a mountain laurel dominated understory, found a mean fire frequency of 12.7 years and a fire rotation period of 10 to 40 years between 1856 and 1940. This period coincides with increased burning by European settlers, decreased native American burning, and decreased burning from natural ignitions due to fire suppression policies.
In pitch pine forests in New Jersey, fire intervals in stands where mountain laurel is dominant or codominant vary from 5 to 60 years . In these stands, increases in the density of mountain laurel over the past century are speculated to be strongly linked to the length of time between fires. Windisch  found that unburned stands (>50 years) contain higher densities of mountain laurel than those that have recently burned .
The following table provides fire return intervals for plant communities and ecosystems where mountain laurel is important. 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".
|Community or Ecosystem||Dominant Species||Fire Return Interval Range (years)|
|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|
|beech-sugar maple||Fagus spp.-Acer saccharum||>1,000|
|black ash||Fraxinus nigra||<35 to 200|
|yellow-poplar||Liriodendron tulipifera||<35 |
|northeastern spruce-fir||Picea-Abies spp.||35-200 |
|southeastern spruce-fir||Picea-Abies spp.||35 to >200 |
|red spruce*||Picea rubens||35-200 |
|shortleaf pine||Pinus echinata||2-15|
|shortleaf pine-oak||Pinus echinata-Quercus spp.||<10|
|longleaf pine-scrub oak||Pinus palustris-Quercus spp.||6-10|
|Table Mountain pine||Pinus pungens||<35 to 200 |
|red-white-jack pine*||Pinus resinosa-P. strobus-P. banksiana||10-300 [32,51]|
|pitch pine||Pinus rigida||6-25 [15,53]|
|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-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 |
|aspen-birch||Populus tremuloides-Betula papyrifera||35-200 [32,119]|
|black cherry-sugar maple||Prunus serotina-Acer saccharum||>1,000 |
|oak-juniper woodland (Southwest)||Quercus-Juniperus spp.||<35 to <200 |
|northeastern oak-pine||Quercus-Pinus spp.||10 to <35 |
|oak-gum-cypress||Quercus-Nyssa-spp.-Taxodium distichum||35 to >200 |
|southeastern oak-pine||Quercus-Pinus spp.||<10|
|white oak-black oak-northern red oak||Quercus alba-Q. velutina-Q. rubra||<35|
|northern pin oak||Quercus ellipsoidalis||<35|
|bear oak||Quercus ilicifolia||<35|
|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|
|eastern hemlock-yellow birch||Tsuga canadensis-Betula alleghaniensis||>200 |
|elm-ash-cottonwood||Ulmus-Fraxinus-Populus spp.||<35 to 200 [32,119]|
|Prescribed fire burning in a mixed hardwood forest with an understory of mountain laurel during the fall of 2004 in Pennsylvania. Credits: Tomas Liogys, Senior Firefighter, Delaware Water Gap National Recreation Area.|
IMMEDIATE FIRE EFFECT ON PLANT:
Fire top-kills mountain laurel [120,132].
DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
Fire effects to mountain laurel vary with season, severity, and intensity and range from partial consumption to complete consumption of the aboveground plant. Leaves of mountain laurel are reported to burn at high intensity; burning shrubs can produce flame lengths of 100 feet (30 m) . The combustible nature of mountain laurel is suspected to be due to the oil or wax content of the leaves . Also, fire behavior characteristics are thought to be highly associated with live fuel moisture. In the southern Appalachians, leaf moisture content of mountain laurel is highest (70%) in new growth and declines as leaves mature. Live fuel moisture of leaves, twigs, and stems greater than 1-year-old average 50% to 60% moisture content (see: Seasonal development) .
PLANT RESPONSE TO FIRE:
Mountain laurel sprouts from basal burls or by layering or suckering "prolifically" regardless of fire intensity, severity, or frequency [36,45,131,133].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
The majority of research that has investigated mountain laurel fire effects is in the context of silvicultural management for improvement of hardwood or pine forest yields. In these forests, dense thickets of mountain laurel are commonly thought to be in greater abundance than during the presettlement era. In addition, these thickets are speculated to restrict regeneration of oak and other desirable hardwood species by quickly outgrowing and limiting light resources in early-successional postharvest stands. Thus, fire management in these forests centers around the use of prescribed fire to reduce the abundance and competitive influence of mountain laurel. Typical treatments involve the removal of merchantable timber and cutting and felling the remaining woody stems and abandoning them as slash in the spring after leaf out. As the slash dries, sprouts of less desirable species such as mountain laurel emerge and are burned during the mid-summer. Much of the research focuses on the effects of varying fire intensities and frequencies on postfire sprouting of mountain laurel [22,24,54,114,117].
Fire severity/intensity: Mountain laurel responds to burning by sprouting abundantly after burning regardless of fire intensity.
Two prescribed fires (one in 1984 and another in 1985) were used in combination with a felling treatment in Connecticut to asses the postfire response of mountain laurel in a 70-to 80-year-old oak-hardwood stand. Burning was conducted in the spring. Each stand endured both low- and high-severity fires which were measured as <30% or >70% postfire reduction in tree stem density when compared to adjacent stands. After burning, mountain laurel sprouted "quickly" and grew "vigorously" resulting in heights higher than in adjacent unburned control stands 8 and 9 years after fire. The most vigorous mountain laurel growth occurred in the severely burned area where overstory mortality was greatest . The following table represents average annual height growth rates of mountain laurel in all treatments.
|Severe Burn||Moderate Burn||Unburned Control|
|3.9 inches/year||3.1 inches/year|
A lightning caused wildfire in July 1988 at Virginia's Shenandoah National Park in a Table Mountain-pitch pine forest revealed that mountain laurel sprouts quickly after a variety of burn severities. Mountain laurel's sprouting response was stronger in the more severe burn. Fire severity was assessed by measuring postfire cumulative tree mortality, crown scorch, and stem char. The following table represents mountain laurel importance values 1 and 2 years postfire.
Mountain laurel sprouted "rapidly" after spring burning in an Appalachian Mountain oak forest with a mountain laurel dominated understory. Increases in mountain laurel stems per hectare resulted after 2 separate fires each representing low- to high-severity fire when compared to adjacent unburned control stands. Low fire severity was characterized by the authors  as a surface fire with limited torching of overstory trees, while severe fire severity was characterized by extensive overstory torching and mortality. Low fire severity resulted in higher densities of mountain laurel after 7 years possibly because of mountain laurel's preference for shady sites. The following table represents mountain laurel stems per hectare 7 years postfire:
|Control||Low-severity fire||Severe fire|
Mountain laurel sprouted vigorously after an experimental restoration treatment involving felling and burning at low severity in a southern Appalachian xeric pine-hardwood forest. Thirteen years after burning, mountain laurel had established 21,525 stems per hectare . Similar studies conducted by Clinton and Vose  and Elliott and others  found comparable results.
Fire frequency: The ability of mountain laurel to reproduce after repeated fire has been noted in several studies.
In xeric pine-hardwood forests near the Red River Gorge in Kentucky, a prescribed fire and a subsequent wildfire 2 years afterwards provided an opportunity to study the effects of multiple burns on mountain laurel reproduction in 4 types of stands: (1) adjacent unburned, (2) once burned (prescribed fire 1993), (3) once burned (wildfire 1995), (4) and twice-burned (1993 and 1995). All burning occurred in the spring. Sampling was conducted in August of 1997, 3 growing seasons after the wildfire of 1995 and 5 years following the 1993 prescribed fire. Post-fire reproduction strategy of new mountain laurel stems was unknown. After burning, new seedlings and/or sprouts were most frequently observed growing underneath dead mountain laurel branches. Mountain laurel increased in percent cover in all burns. The largest increase in percent cover of mountain laurel was in the twice-burned plots . Average percent cover of mountain laurel was as follows.
|control||1993 burn||1995 burn||1993& 1995 burns|
A fire history study in pine barren forests of New Jersey and New York analyzed current vegetation patterns in relation to fire frequency. In this habitat type mountain laurel is considered a strong sprouter that historically tolerated short fire intervals (< 15 years) .The following Research Project Summaries provide information on prescribed fire use and postfire response of plant community species including mountain laurel:
Allometric equations for estimating dry biomass  have been used for predicting fuel loadings of mountain laurel leaf, branch, and bole.
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Mountain laurel's leaves, buds, flowers and fruits are poisonous and may be lethal to livestock and humans [4,77]. However, white-tailed deer, eastern cotton tails, black bear, and ruffed grouse are known to utilize this species especially as winter forage or during years of food shortages [30,48,60,61,69,109,110,118].
Palatability/nutritional value: Nutritional values of mountain laurel foliage were analyzed 10 to 12 months after spring burning and in adjacent unburned stands in northeastern Georgia. The authors  believed that their methodology underestimated crude fat values. Percent composition of mountain laurel foliage before and after burning follows:
|Nitrogen (free extract)||71.0||70.9|
Cover value: Animals that associate with mountain laurel include white-tailed deer, eastern screech owl, black bear, ruffed grouse, and various song bird species [104,109,110]. Black bears are known to den in "ground nests" in mountain laurel thickets .VALUE FOR REHABILITATION OF DISTURBED SITES:
Wood Products: Mountain laurel wood is heavy (green weight: 63 lbs/ft3), hard (1,790 lbf), and strong, but rather brittle, with a close straight grain. Mountain laurel sapwood is yellow, while the heart wood is yellow-brown with red spots . The wood of mountain laurel has a long history of uses by native and Euro-Americans. It has been used in the manufacturing of pipes, wreaths, roping, furniture, bowls, utensils, and various other household goods and novelties. Economically, mountain laurel is the most important member of the genus Kalmia. The species is sold commonly as an ornamental and the foliage is used in floral displays [4,60].OTHER MANAGEMENT CONSIDERATIONS:
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