|© Pat Breen, Oregon State University|
Dwarf birch hybridizes with arctic dwarf birch (Betula nana subsp. exilis and Betula nana subsp. nana) where their ranges overlap [54,77,159]. Dwarf birch also hybridizes with paper birch (Betula papyrifera) in interior Alaska . Numerous other hybrids have been described including:
Betula × sargentii Dugle (B. nana × B. pumila)
Betula × eastwoodiae Sargent (B. nana × B. occidentalis) [31,51,54]
Betula × dugleana Lepage (B. nana × B. neoalaskana)
Betula × dutillyi Lepage (B. nana × B. minor, a putative hybrid)  LIFE FORM:
FEDERAL LEGAL STATUS:
No special status
Information on state-level protected status of plants in the United States is available at Plants Database.
Dwarf birch is characteristic of many mixed shrub and tussock tundra communities in Alaska and northern Canada [1,2,10,149]. In southwestern Canada and the contiguous United States, dwarf birch often occurs on wetland sites including bogs, fens and carrs, within lodgepole pine (Pinus contorta), Engelmann spruce (P. engelmannii), or subalpine fir (Abies lasiocarpa) forest types and is often associated with alders (Alnus spp.) and willows (Salix spp.) [15,22,84,86,110].
Dwarf birch is listed as a dominant species in the following vegetation classifications:United States―
black spruce/dwarf birch/feather moss (Hylocomium spp.) vegetation type
black spruce/dwarf birch-marsh Labrador tea/sphagnum (Ledum palustre/Sphagnum spp.) vegetation type
black spruce-white spruce/dwarf birch vegetation type 
black spruce-white spruce/dwarf birch/feather moss community 
black spruce-white spruce/dwarf birch/reindeer lichen (Cladonia spp.) community 
black spruce-white spruce/thinleaf alder (Alnus incana ssp. tenuifolia)-dwarf birch/Schreber's big red stem moss (Pleurozium schreberi) vegetation type
dwarf birch vegetation type
dwarf birch-blueberry/rough fescue (Vaccinium spp./Festuca altaica)/feather moss-lichen vegetation type
dwarf birch-blueberry/Bigelow's sedge (Carex bigelowii) vegetation type
dwarf birch-bog blueberry-black crowberry (Vaccinium uliginosum-Empetrum nigrum)- marsh Labrador tea/lichen vegetation type
dwarf birch-bog blueberry/sedge (Carex spp.)/sphagnum vegetation type
dwarf birch-bog rosemary (Andromeda polifolia)/sphagnum vegetation type
dwarf birch-diamondleaf willow (Salix planifolia)-bog blueberry vegetation type
dwarf birch-mountain cranberry-cloudberry (Vaccinium vitis-idaea-Rubus chamaemorus)/sphagnum vegetation type
dwarf birch-marsh Labrador tea-blueberry vegetation type
dwarf birch-marsh Labrador tea/mountain cranberry/wideleaf polargrass (Arctagrostis latifolia) vegetation type
dwarf birch/Schreber's big red stem moss-mountain-fern moss (H. splendens) vegetation type
dwarf birch-sweet gale (Myrica gale)-bog rosemary/sphagnum vegetation type
dwarf birch-sweet gale/sedge/sphagnum vegetation type
dwarf birch-willow (Salix spp.)-marsh Labrador tea/Bigelow's sedge/feather moss-lichen vegetation type
dwarf birch-willow-thinleaf alder vegetation type
mountain alder (Alnus viridis subsp. crispa)-dwarf birch-marsh Labrador tea/sphagnum vegetation type
paper birch/dwarf birch/feather moss vegetation type
shrubby cinquefoil (Dasiphora fruticosa ssp. floribunda)- sweet gale-dwarf birch-black crowberry/sphagnum vegetation type
shrubby cinquefoil-sweet gale-dwarf birch-marsh Labrador tea/feather moss vegetation type
white spruce/dwarf birch/feather moss-reindeer lichen vegetation type
white spruce/dwarf birch/reindeer lichen vegetation type
white spruce/dwarf birch/sphagnum vegetation type
white spruce/dwarf birch/mountain-fern moss vegetation type 
diamondleaf willow-dwarf birch shrub association 
willow-dwarf birch type 
Wolf's willow (S. wolfii)-dwarf birch-shrubby cinquefoil shrub association 
dwarf birch/woollyfruit sedge (C. lasiocarpa) community type 
dwarf birch dominance type 
dwarf birch/tufted hairgrass (Deschampsia caespitosa) community type 
dwarf birch/woollyfruit sedge community type 
grayleaf willow (S. glauca)-dwarf birch-shrubby cinquefoil shrub type 
dwarf birch-kinnikinnick (Arctostaphylos uva-ursi) shrub carr association 
white spruce/willow (Salix spp.)-dwarf birch zone 
dwarf birch/star reindeer lichen (Cladonia alpestris)-moss community (Kershaw 1984, cited in )
birch (Betula spp.) vegetation association 
balsam poplar (Populus balsamifera)/dwarf birch/arctic lupine (Lupinus arcticus) vegetation type
black spruce/dwarf birch-marsh Labrador tea vegetation type 
dwarf birch/rough fescue community 
dwarf birch-bog blueberry-reindeer lichen vegetation type
cloudberry-dwarf birch-bog blueberry vegetation type
lichen-dwarf birch-marsh Labrador tea vegetation type 
white spruce/dwarf birch/water sedge (Carex aquatilis) community 
Dwarf birch is a deciduous, long-lived shrub. Plants are low and spreading to erect with 1 to several main stems. Dwarf birch ranges from 8 inches (20 cm) tall on upland sites and in arctic environments to 10 feet (3 m) in drainages and in more southern areas [31,44,60,76,77,77,102,137,159,168]. The bark is thin, smooth, and does not peel readily [51,75,159,168]. Leaves are thick and leathery and range from 0.2 to 1.2 inches (0.5-3 cm) long and 0.2 to 0.8 inch (0.5-2 cm) wide [75,76,77,159]. The inflorescences are catkins. Male catkins are 0.4 to 1 inch (10-25 mm) long, and female catkins are 0.3 to 0.8 inch (7-20 mm) long [31,159,168]. Fruits are narrow-winged, single-seeded samaras 1 to 1.5 mm long and wide [31,41,104]. Rhizomes are 0.8 to 2.4 inches (2-6 cm) thick and are found in the top 2.4 inches (6 cm) of soil . Dwarf birch has an extensive root system [24,42,104]. Roots are ectomycorrhizal, an adaptation to arctic and alpine soils that are generally low in inorganic nitrogen and phosphorus [37,145].RAUNKIAER  LIFE FORM:
Pollination: Dwarf birch is wind pollinated. In a dwarf birch population on Baffin Island, Northwest Territories, female catkins were smaller and contained 50% fewer flowers than were contained in female catkins from a more southern site in subarctic Quebec. There was an estimated 10-fold difference in pollen dispersed between the 2 sites. At the northern extent of its distribution, dwarf birch is clonal, and the distance between genetically distinct individuals is great. In these areas, female catkins are more likely to receive incompatible pollen, preventing fertilization from occurring .
Breeding system: Dwarf birch is monoecious [64,104]. Plants are not self fertile .
Seed production: Dwarf birch produces numerous catkins, each of which yields 30 to 50 samaras . Seed production is generally high in more southern parts of its range [30,42,73]. In more northern areas, production of viable seed is limited by the shorter growing season, lower temperatures, and distance between genetically distinct individuals .
Seed dispersal: Dwarf birch seeds are dispersed in their samaras. Wind, water, and sometimes gravity disperse the samaras. Samaras may blow across crusted snow [11,44,104].
Seed banking: Dwarf birch produces numerous, tiny seeds and has a transient seed bank. In a review of the literature, Karrfalt  states that birch seeds may be abundant in the soil but the seeds are generally short lived. Rowe 1983  states that viable dwarf birch seeds are "rare" in the soil seed bank. Dwarf birch seeds were present, however, in the first 1.2 inches (3 cm) of soil collected from alpine sites on the Gaspé Peninsula, Quebec . Results of this study are provided in the table below.
Dwarf birch seed production and density on sites in Quebec 
|Site||Total seeds/m²||Viable seeds/m²||% cover in aboveground vegetation|
Germination: Prechilling improves germination of dwarf birch seeds. Optimum germination temperature for many arctic species is 59 to 86 °F (15-30 °C) . The germination rate of dwarf birch seeds collected from alpine sites in the White Mountains, New Hampshire, was 25% for refrigerated seeds and 4% for unrefrigerated seeds. Days required for germination ranged from 14 to 28 for refrigerated seeds and from 27 to 299 for unrefrigerated seeds .
Seed viability varies with latitude. At the northern range limit of dwarf birch on Baffin Island, <0.5% of seeds were viable. Very few samaras contained seeds with fully developed embryos. At a southern site in subarctic Quebec, 70% of seeds were viable [166,167]. Seeds that overwinter on plants remain viable until they disperse the following spring .
Seed germination and samara weight may be correlated. In a germination study in Kuujjuaq, Quebec, no seeds from samaras weighing <0.09 mg germinated, few samaras weighing <0.12 mg had seed that germinated, and all samaras weighing >0.34 mg had seed that germinated . Germination of wind-dispersed seeds may be highest on exposed mineral soils .
Seedling establishment/growth: Seedling recruitment rates in dwarf birch populations are usually very low. Site disturbance by fire increases the likelihood of seedling establishment . Although recruitment from seed is almost nonexistent in northern dwarf birch populations, plants of all age classes were evident in a southern Quebec population [73,166]. Seedling growth is very slow, and seedling mortality is often high [41,44].
Vegetative regeneration: Dwarf birch reproduces vegetatively by branch layering and sprouting from dormant buds on the root crown and rhizomes [26,44]. Dwarf birch is clonal in the northern parts of its range .
Dwarf birch occupies a wide variety of sites, ranging from rocky subarctic and alpine tundra to deep, organic, boreal soils . It is typically a wetland species occurring most commonly on moist, acidic, and nutrient-poor organic sites including fens, swamps, bogs, muskegs, wet meadows, lake and stream margins, and seepage areas [22,31,48,60,75,76,77,159,168]. Bog birch is also found on upland sites including eskers, till ridges, rock outcrops covered with shallow soil, cliffs, sandy hillsides, and rocky ridges [5,31,51,82,137]. It dominates open valley bottoms in the Canadian Rocky Mountains  and is the most common shrub at treeline in interior Alaska, forming a nearly continuous zone between the treeline and alpine tundra in many areas .
Elevation: Dwarf birch occurs between 1,300 and 11,000 feet (400-3,400 m) across its range [66,75,79,80,123,125,168]. Elevational ranges are summarized below.
Elevational ranges for dwarf birch by state or province
|Sierra Nevada||6,500-8,500 |
|Nova Scotia||1,300 |
Temperature: Dwarf birch is tolerant of cold temperatures. It is common in black spruce forests in the Yukon where the mean annual temperature is 27 °F (-3 °C) . Frost tolerance in dwarf birch is high, and dwarf birch grows abundantly over large areas of permafrost . Dwarf birch tolerates severe winter temperatures by withdrawing water from the protoplast and freezing it in the cell walls .
Moisture: Although it is primarily a wetland plant, dwarf birch does not appear to tolerate continuous flooding. In bogs near Fairbanks, Alaska, dwarf birch abundance decreases as soil moisture increases. Dwarf birch is also more "vigorous" in communities that support taller tussocks . In the Cariboo Forest Region of British Columbia, dwarf birch is common in wetlands that have no standing water late in the season . In Montana, however, the water table is often within the rooting zone of dwarf birch throughout the summer, and dwarf birch grows in soils that remain flooded until midsummer or are saturated year-round . In a willow (Salix spp.)-dwarf birch community near Churchill, Manitoba, the depth of the water table averaged 3 inches (6.5 cm) below the surface, and soil moisture in the organic layer was 63% . Dwarf birch is an indicator of "substantial groundwater" in the North Thompson River valley, British Columbia .
Annual precipitation ranges from 4 to 9 inches (109-230 mm) on 2 northern Canadian study sites where dwarf birch is abundant [6,24]. While some authors describe dwarf birch as drought intolerant , in a review of the literature de Groot and others  state that dwarf birch appears tolerant of periodic drought.
Soils: Dwarf birch grows in a variety of soils, ranging from sandy and gravelly loam on river terraces to poorly drained, organic soils in bogs, muskegs, and other wetland habitats [43,64,114,121,141]. It is tolerant of moderate salinity  and pH ranging from 3.1 to 6.5 [105,141].SUCCESSIONAL STATUS:
The table below summarizes an analysis of 5 stands representing a vegetation chronosequence on gravel outwash of the Muldrow Glacier in Denali National Park, Alaska. Dwarf birch was not present in the earliest successional stage but was abundant in intermediate stages and persistent in the oldest stands .
|Frequency (%) and cover (%) of dwarf birch at 5 successional stages |
|Pioneer stage (25-30 years)||0||0|
|Meadow stage (100 years)||80||<5|
|Early shrub stage (150-200 years)||100||50-75|
|Late shrub stage (200-300 years)||100||50-75|
|Climax tundra (5,000-9,000 years)||100||25-50|
|Flowering dates for dwarf birch by region|
|Sierra Nevada, California||April-June |
|Gaspé Peninsula, Quebec||June-August |
Fruits mature between July and October and can persist through the winter [104,106,159,166]. Samara dispersal occurs in the fall, just prior to snow fall, and in the following spring soon after snow melt [78,166]. Leaves begin to senesce in late summer, and leaf abscission is complete by late September .
Phenological stages for dwarf birch in a valley-bottom floodplain in west-central Alberta are summarized below.
|Seasonal development of dwarf birch in west-central Alberta |
|5 May||most plants initiating leaf-break|
|10 June||male catkins dropped; female catkins small and turning darker green|
|29 June||female catkins at mature size|
|11 Aug.||female catkins brown; terminal buds large|
|1 Sept.||half of leaves on most plants yellow|
Fire regimes: Dwarf birch is adapted to a wide range of fire regimes, from subarctic and alpine areas that seldom burn to boreal environments that burn frequently [42,44]. Wetland areas where dwarf birch grows burn infrequently due to the high moisture content of the vegetation and soil. These sites sometimes act as firebreaks. Fires do occur, however, during dry summers or in the spring and fall when the vegetation is dry [35,43,44,86,104,143].
In interior Alaska, dwarf birch is found on poorly drained and permafrost underlain sites occupied primarily by black spruce stands, muskegs, and bogs. These types are widespread in Alaska and burn frequently [154,158]. Black spruce-birch (Betula spp.) is the most widespread forest type in interior Alaska and also the type with the highest frequency of fire . Native Americans were an important cause of fires in the black spruce-birch ecosystem . Fire frequency increased with the increase in mining activity in the 1800s . Today, most fires are lightning caused [70,95]. Between 1940 and 1969, lightning was responsible for 78% of the area burned in interior Alaska .
Fires occur in interior Alaska between 1 April and 30 September. Most fires occur in May, June, and July, corresponding with the highest annual temperatures, longest day length, lowest humidity and precipitation, and high winds [55,154]. Fires can occur, however, whenever fuels are not covered with snow and are exposed to sufficiently warm temperatures and drying winds .
Fire years are sporadic in occurrence but tend to occur at least once every decade . “Exceptional fire years” are characteristic of the black spruce-birch ecosystem. In Alaska, 6 years (1941, 1950, 1957, 1969, and 1977) accounted for 63% of the total area burned between 1940 and 1978 . The average acreage burned each year in interior Alaska is approximately 1 million acres . Fires tend to be large and may spread over thousands to hundreds of thousands of acres or more [71,94,150].
Estimated fire-return intervals in the black spruce-birch ecosystem vary from 50 to 200 years [71,160]. Fires occur every 50 to 70 years in black spruce-white spruce/bog birch/reindeer lichen communities in interior Alaska . Heinselman  estimates a fire-return interval of 130 years for open black spruce/reindeer lichen forest and 100 years for closed-canopy black spruce forest. Mean fire-return intervals in lowland black spruce forests on the Kenai Peninsula, Alaska, range from 89 to 195 years [4,97].
Black spruce-birch communities experience high-severity, stand-replacing fires. These communities are highly flammable due to the abundance of ericaceous shrubs, the prevalence of dead, low-hanging branches on the black spruce trees, which are often covered with highly flammable epiphytic lichens, and the thick moss and lichen mats that cover the forest floor and become highly flammable after periods of low rainfall [94,95,155]. There is often nearly continuous fuel from the forest floor to the tree crowns . Most fires in black spruce-birch communities are either crown fires or ground fires severe enough to damage or kill aboveground vegetation, including overstory trees. Fires may be severe enough to completely expose the mineral soil layer [50,71,150,160].
The following table provides fire return intervals for plant communities and ecosystems where dwarf birch is important. Find 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-return intervals for plant communities with dwarf birch|
|Community or Ecosystem||Dominant Species||Fire Return Interval Range (years)|
|birch||Betula spp.||80-230 |
|tamarack||Larix laricina||35-200 |
|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 |
|jack pine||Pinus banksiana||<35 to 200 [34,50]|
|Rocky Mountain lodgepole pine*||Pinus contorta var. latifolia||25-340 [16,17,144]|
|aspen-birch||Populus tremuloides-Betula papyrifera||35-200 [50,161]|
|quaking aspen (west of the Great Plains)||Populus tremuloides||7-120 [7,62,103]|
|Rocky Mountain Douglas-fir*||Pseudotsuga menziesii var. glauca||25-100 [7,8,9]|
|Changes in root biomass and root phosphorus in dwarf birch before and after fire |
|Root characteristics||Mature (140-year-old)||Burned (0-year-old)||Change (%)|
|root biomass (kg/ha)||9,159||8,886||-4|
|concentration of P in roots (% dry weight)||0.047||0.133||+283|
|mass of P in roots (kg/ha)||4.30||11.80||+274|
Dwarf birch increases after low- to moderate-severity fires . Repeated fires near treeline and on some wet sites in Alaska and northern Canada result in thickets of dwarf birch, mountain alder, and willows (Salix spp.) [82,154]. On tundra sites near Inuvik, Northwest Territories, total vascular plant cover on a burned area was more than twice that on an adjacent unburned area. The increase was due in large part to dwarf birch, which increased 8.8% after the burn .
Because of its ability to sprout from the root crown and rhizomes, dwarf birch is among the first plants to regenerate after fire in many communities [26,43,44,69,105,149,150]. Dwarf birch also persists into middle and late successional stages [23,105,133,149,150]. It was present in all postfire successional stages observed in a black spruce/reindeer lichen woodland in northern Quebec, but was most abundant in the intermediate stages between approximately 20 and 50 years after fire . Frequency of dwarf birch at each successional stage is summarized below.
|Frequency (%) of dwarf birch at 4 postfire stages |
|postfire year 5||postfire year 20||postfire year 50||postfire year 90|
In subarctic black spruce forests of western Labrador, dwarf birch was most abundant 18 to 40 years after fire. Mean canopy volume of dwarf birch between 2 and 140 years after fire is summarized below .
|Mean canopy volume (m³) of dwarf birch across 5 postfire successional stages |
|postfire year 2||postfire year 18||postfire year 40||postfire year 80||postfire year 140|
Low-severity fire and spring burning promote sprouting in dwarf birch. In a study conducted during the 1992 growing season in the Rocky Mountains of Alberta, dwarf birch plants were burned in low-, medium-, and high-severity treatments. Plants burned earlier in the growing season and in low-severity treatments produced more and taller sprouts by the end of the first year after burning than plants burned late in the growing season or in severe fire treatments. Dwarf birch in the high-severity treatments sprouted latest. Following high-severity fire, new sprouts originated from the bottoms of rhizomes, indicating mortality of buds closer to the soil surface. No sprouting occurred on plants burned after late June, which may be related to seasonal variation in plant hormones that release buds from dormancy and promote stem extension in dwarf birch. Fall burning resulted in greatest plant mortality than spring and summer burning. Some plants burned in the fall sprouted the following year [43,44].
Dwarf birch was more abundant in "lightly" burned areas than in "heavily" burned areas following a June 1971 wildfire in black spruce forest near Fairbanks, Alaska . Density of dwarf birch for 4 years following the fire is provided below.
|Dwarf birch density (stems/ha) after wildfire in heavily and lightly burned areas |
|postfire year 1||postfire year 2||postfire year 3||postfire year 4|
The response of dwarf birch to fire in a valley-bottom floodplain in the Rocky Mountains of Alberta varied with fire severity. Dwarf birch stem density increased for 2 years after a spring prescribed, low-severity fire in 1984 due to abundant sprouting. Following high-severity burns in 1987 and 1993, however, both stem density and canopy cover sharply declined. Results of this study are given in the figure below .
Although survival of dwarf birch plants decreases when fire severity is high, seedlings establish more easily on the bare mineral soil that is exposed after a high-severity fire [23,42].
On some sites, including in Wisconsin fens, dwarf birch increases in the absence of fire . In the Rocky Mountains of Alberta, dwarf birch forms extensive, closed-canopy stands where fire has been excluded .DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Prescribed burning at 3- to 6-year intervals in the Rocky Mountain foothills of Alberta has decreased shrub cover and increased forage production . Dwarf birch cover decreased by 35% following a moderate-severity, prescribed spring fire in wood bison habitat in Fort Providence, Northwest Territories. After 3 months, dwarf birch cover increased by 26% . Due to dwarf birch's "vigorous" sprouting response, burning at regular intervals is necessary to minimize its regrowth .
Fuel potential of dwarf birch is low because leaf moisture content is high . Moisture content of dwarf birch measured near Inuvik, Northwest Territories, is given in the table below .
|Moisture content (%) of dwarf birch in dry and wet tundra |
|18 July||1 August||15 August|
Numerous wildlife species eat dwarf birch, including moose, mule deer, white-tailed deer, Rocky Mountain elk, mountain goats, caribou, grizzly bears, American black bears, small mammals, birds, and insects [14,68,74,81,91,109,126,146,159]. Dwarf birch is a "preferred" browse species for game animals in Teton County, Wyoming . It is dominant in tamarack swamps in southwestern Manitoba. These swamps provide habitat for moose, jumping mice, northern river otters, shrews, Canada jays, black-capped chickadees, white-throated sparrows, and Connecticut warblers .
Moose: Dwarf birch accounted for 11.8% of summer and 0.7% of winter moose forage on the Red Rock Lakes National Wildlife Refuge . It is preferred browse in Banff and Jasper National Parks, Alberta , but is not preferred by moose in Alaska .
Caribou: Buds, leaves, and sprouts of dwarf birch are preferred foods for caribou in Alaska in the spring and early summer. The rumens of 6 caribou examined in mid-June contained almost exclusively bog birch. Caribou eat the leaves extensively into June and July, but by mid-September the leaves are less palatable than willow (Salix spp.) leaves [135,159]. Caribou also eat dwarf birch in summer and winter in northern Canada [20,36,72,128]. Heavy browsing by the Rivière George caribou herd in northern Quebec depleted winter carbohydrate reserves in dwarf birch, leading to decreased dwarf birch growth in spring .
Birds: Several species of ptarmigan and grouse eat dwarf birch in Alaska, Canada, and the contiguous northern United States [107,159]. Sharp-tailed grouse and greater prairie-chickens eat dwarf birch buds in Wisconsin in the winter , and spruce grouse eat dwarf birch seeds in central Alaska . Dwarf birch and dwarf birch buds and catkins comprised 11% of the food in rock ptarmigan crops in Alaska in spring, 12% in summer, 45% in fall, and 79% in winter. For willow ptarmigan the 2 birches comprised 0% of food in crops in spring, 3% in summer, 4% in fall, and 12% in winter .
Small mammals: American beavers eat dwarf birch . Dwarf birch is a preferred winter food of snowshoe hares in the southwestern Yukon [39,88,122,136]. Eastern heather voles eat dwarf birch bark in the winter in Canada . White spruce/dwarf birch communities in the Kluane Region, Yukon, provide habitat for a number of small mammals including deer mice, northern red-backed voles, meadow voles, and heather voles .
Fish: Dwarf birch provides overhanging shade and cover for fish along low-gradient streams in western Montana .
Insects: Insect herbivores can cause "moderate" damage to dwarf birch. During the 1976 to 1980 growing seasons, dwarf birch plants in northern Quebec lost 20% to 50% of leaf biomass to insects . In Alaska, the total number of herbivorous insects decreased with increases in latitude and altitude and distance from the white spruce forest zone. More detailed information on insects found on dwarf birch foliage is available .
Dwarf birch importance rankings for 9 ungulate species in British Columbia are provided below.
|Importance of dwarf birch in the diets of ungulates in British Columbia |
|Sitka black-tailed deer||low|
|Rocky Mountain elk||moderate|
Palatability/nutritional value: The palatability of dwarf birch in several states is as follows
|Palatability of dwarf birch for livestock and wildlife [28,38,46,67,125]:|
The energy and protein values of dwarf birch are low . Sugar content in dwarf birch leaves declines in late summer. Nitrogen concentration in leaves peaks early in spring then declines throughout the growing season . Nutritive values measured in dwarf birch plants near Inuvik, Northwest Territories, are given in the table below [129,130].
|Nutritive values in dwarf birch twigs and leaves [129,130]|
|Plant part||Month||Cu||Mo||Fe||Mn||Zn||K||Mg||Ca||P||crude fat||crude fiber||crude protein|
* No data available.
Dwarf birch produces carbon and nitrogen-based antiherbivore compounds that deter browsing . Sugar and nitrogen content is highest in the leaves in early spring. Dwarf birch allocates the greatest portion of its photosynthate to the production of antiherbivore phenolics at that time; otherwise, leaves would be susceptible to browsing insects .
Cover value: The table below summarizes thermal or feeding cover values of dwarf birch.
|Cover values of dwarf birch for wildlife in 3 western states [28,46]|
|upland game birds||good||fair||fair|
|small nongame birds||good||fair||good|
Dwarf birch provides cover for willow, rock, and white-tailed ptarmigan in southwestern Yukon . Grizzly bears in the central Canadian Arctic constructed their dens under dwarf birch cover more than any other plant species. Dwarf birch was present at 84% of 52 den sites, and it was the highest in percent cover around den entrances. Dwarf birch roots formed ceilings of several dens studied .VALUE FOR REHABILITATION OF DISTURBED SITES:
Black spruce seedling survival after fire in the boreal forest may be facilitated by shading from dwarf birch and other shrubs that reproduce vegetatively and grow quickly .OTHER USES:
Expanding dwarf birch populations on Canadian Rocky Mountain rangelands reduce forage for elk, bison, and other grazing animals. Removal of bog birch increases the production of forage grasses .Information on the effects of herbicides on dwarf birch is available in Chapin and others .
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