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Betula nana subsp. exilis (Sukatsch.) Hult., dwarf birch [31,34,44,92]
Betula nana subsp. nana, arctic dwarf birch [31,34]
Dwarf birch hybridizes with resin birch (Betula glandulosa) where their ranges overlap [31,44,92]. Horne birch (Betula × hornei Butler) is the hybrid between dwarf birch and paper birch (Betula papyrifera) [92].
LIFE FORM:AK |
AB | BC | MB | NF | NT | NS | NU | PQ | SK | YK |
BLM PHYSIOGRAPHIC REGIONS [5]:
None
KUCHLER [53] PLANT ASSOCIATIONS:
K094 Conifer bog
SAF COVER TYPES [29]:
12 Black spruce
13 Black spruce-tamarack
18 Paper birch
201 White spruce
202 White spruce-paper birch
203 Balsam poplar
204 Black spruce
217 Aspen
222 Black cottonwood-willow
251 White spruce-aspen
252 Paper birch
253 Black spruce-white spruce
254 Black spruce-paper birch
SRM (RANGELAND) COVER TYPES [76]:
901 Alder
904 Black spruce-lichen
907 Dryas
911 Lichen tundra
912 Low scrub shrub birch-ericaceous
913 Low scrub swamp
916 Sedge-shrub tundra
917 Tall shrub swamp
918 Tussock tundra
919 Wet meadow tundra
920 White spruce-paper birch
921 Willow
HABITAT TYPES AND PLANT COMMUNITIES:
Dwarf birch is characteristic of low, open, mixed-shrub and tussock tundra
communities. It is also found in black spruce (Picea mariana) and white spruce
(P. glauca) communities including black spruce-birch (Betula spp.),
the most widespread ecosystem type in Alaska [1,36,84,88,91].
Dwarf birch is listed as a dominant species in the following vegetation classifications:
United States―alpine sweetgrass (Hierochloe alpina)-dwarf birch community [95]
Bigelow's sedge-water sedge (Carex bigelowii-C. aquatilis)-dwarf birch vegetation type
black spruce/dwarf birch/cottonsedge/sphagnum (Eriophorum spp./Sphagnum spp.) vegetation type
black spruce/dwarf birch/sedge (Carex spp.) vegetation type
black spruce/dwarf birch-shrubby cinquefoil (Dasiphora fruticosa ssp. floribunda)/sedge vegetation type
black spruce/thinleaf alder (Alnus incana subsp. tenuifolia)/dwarf birch-blueberry/reindeer lichen (Vaccinium spp./Cladina spp.) vegetation type
black spruce/thinleaf alder/dwarf birch-marsh Labrador tea (Ledum palustre)/sphagnum vegetation type
black spruce-white spruce/dwarf birch/feather moss (Hylocomium spp.) vegetation type
black spruce-white spruce/dwarf birch-red fruit bearberry-bog blueberry (Arctostaphylos rubra-Vaccinium uliginosum) vegetation type
diamondleaf willow (Salix planifolia)-thinleaf alder/dwarf birch/bluejoint (Calamagrostis canadensis) vegetation type
dwarf birch vegetation type [88]
dwarf birch-bog Labrador tea (L. groenlandicum)/bluejoint reedgrass vegetation unit [90]
dwarf birch-cloudberry (Rubus chamaemorus)-marsh Labrador tea-blueberry vegetation type
dwarf birch-diamondleaf willow/arctic sweet coltsfoot (Petasites frigidus) vegetation type
dwarf birch-diamondleaf willow-bog blueberry vegetation type
dwarf birch-diamondleaf willow-marsh Labrador tea vegetation type
dwarf birch-diamondleaf willow/mountain-fern moss-turgid aulacomnium moss (H. splendens-Aulacomnium turgidum) vegetation type [88]
dwarf birch-marsh Labrador tea community [27]
dwarf birch shrub tundra community [47]
dwarf birch/mountain-fern moss vegetation unit [90]
dwarf birch-willow (Salix spp.)-red fruit bearberry-white arctic mountain heather (Cassiope tetragona)-marsh Labrador tea vegetation type
dwarf birch-willow/water sedge-horsetail (Equisetum spp.) vegetation type
grayleaf willow (S. glauca)-dwarf birch vegetation type
grayleaf willow/eightpetal mountain-avens (Dryas octopetala)-dwarf birch vegetation type [88]
paper birch/dwarf birch/mountain-fern moss vegetation unit [90]
sweet gale (Myrica gale)-dwarf birch-willow/bluejoint reedgrass-sedge vegetation type
tussock cottongrass (Eriophorum vaginatum)-dwarf birch vegetation type
tussock cottongrass-dwarf birch-diamondleaf willow-marsh Labrador tea-blueberry vegetation type
tussock cottongrass-dwarf birch-diamondleaf willow-marsh Labrador tea-blueberry/Bigelow's sedge vegetation type
tussock cottongrass-dwarf birch-marsh Labrador tea-blueberry/Bigelow's sedge vegetation type
tussock cottongrass-dwarf birch-marsh Labrador tea-blueberry vegetation type
tussock cottongrass-dwarf birch-marsh Labrador tea/sphagnum vegetation type [88]
white spruce/dwarf birch vegetation association [69]
white spruce/dwarf birch-bog blueberry/feather moss vegetation type [88]
white spruce/dwarf birch/mountain-fern moss vegetation unit [66,90]
white spruce/dwarf birch/reindeer lichen vegetation unit
white spruce/dwarf birch/sphagnum vegetation unit [90]
netleaf willow (S. reticulata)-dwarf birch-cloudberry vegetation type
tussock cottongrass-marsh Labrador tea-dwarf birch vegetation type [80]
Dwarf birch is a deciduous, low and spreading shrub. Plants are strongly branching and range from 0.5 to 3 feet (.15-1 m) tall. Twigs are resinous and slightly hairy. Leaves are thick and leathery and range from 0.2 to 0.5 inch (5-12 mm) long and 0.2 to 0.6 inch (5-16 mm) wide. The inflorescences are catkins. Male catkins are 0.4 to 1 inch (10-25 mm) long, and female catkins are 0.2 to 0.4 inch (6-10 mm) long. Fruits are narrow-winged, single-seeded samaras [21,31,44,92]. Dwarf birch has an extensive underground system. Rhizomes and roots account for 80% of total plant biomass [15,16]. Roots are ectomycorrhizal, an adaptation to arctic and alpine soils that are generally low in inorganic nitrogen and phosphorus [20,83].
RAUNKIAER [74] LIFE FORM:Pollination: Dwarf birch is wind pollinated.
Breeding system: Dwarf birch is monoecious [49]. Birches in general are strongly self incompatible [23].
Seed production: Dwarf birch is a prolific seed producer [9,98]. Plants at high altitudes and in cold climates produce few seeds (Elkington 1968, cited in [23]).
Seed dispersal: Dwarf birch seeds are dispersed in their samaras. Wind, water, and sometimes gravity disperse the samaras. Samaras may blow across crusted snow [24,49,63].
Seed banking: In a review of the literature, Karrfalt [49] states that birch seeds may be abundant in the soil, but the seeds are generally short lived. Dwarf birch was not found in the seed bank at an Alaskan arctic study site [28]. At another site near Eagle Summit, Alaska, however, dwarf birch seed was absent from the aboveground vegetation but present between 0 and 24 inches (0-60 cm) in the soil [61]. Dwarf birch also germinated from the seed bank at a northern Finland research site [86].
Germination: Seed germination in dwarf birch varies from 21% to 95% [18,21]. Optimum germination temperature for many arctic species is 59 to 86 °F (15-30 °C) [6]. Stratification improves germination of birch seeds [49]. In a greenhouse experiment, stratification for 5 to 15 days broke seed dormancy in dwarf birch. Stratification for 15 days was required for maximum germination in 14 days at 54 °F (12 °C). A longer period of stratification was required for maximum germination at lower temperatures. Germination occurred at a high temperature (75°F (24 °C)) with no special treatment [48].
Seedling establishment/growth: Although dwarf birch produces abundant seed and seed viability may be as high as 95%, successful establishment from seed is rare [18,28,98]. Dwarf birch seedlings are slow growing [10,21,97]. Dwarf birch had the greatest number of active apical meristems producing leaves, stems, or inflorescences of 8 species studied at Eagle Creek, Alaska. It also had the lowest annual aboveground production [18]. In the spring, nitrogen and phosphorus stored in dwarf birch rhizomes and roots are transported into new leaf and stem tissue aboveground. After early July, the leaves are net exporters of nutrients to the rest of the plant, and by late August belowground tissues have regained their initial spring nitrogen and phosphorus concentrations [15].
Growth rates in dwarf birch increase under increased nutrient availability. In experimentally treated plots in Alaskan moist tussock tundra, dwarf birch became dominant following fertilization with nitrogen and phosphorus. Dominance was attributable to increased growth of individuals already present and not the recruitment of new individuals. Under unfertilized conditions, most axillary buds on dwarf birch plants grow into short shoots. The branching pattern in dwarf birch can change, however, when nutrients are not limiting. Under fertilized conditions, axillary buds that would have produced short shoots are stimulated to produce longer, structural branches. Long shoots produce 2 to 3 times more leaf area than short shoots, increasing the plant's total photosynthetic capacity and allowing a dense dwarf birch canopy to form [10,11]. Dwarf birch also produces more long shoots in response to experimental warming [17,36,42].
Vegetative regeneration: Dwarf birch reproduces vegetatively by layering and by sprouting from the root crown and/or rhizomes after fire and other top-killing disturbances [6,9,27,98].
SITE CHARACTERISTICS:In bogs near Fairbanks, Alaska, dwarf birch abundance decreases as soil moisture increases. Dwarf birch is more "vigorous" in communities that support taller tussocks [12,46]. In a review of the literature, de Groot and others [21] state that bog birch does not appear tolerate continuous flooding but does appear to tolerate periodic drought.
Dwarf birch occurs in circumpolar regions with long, cold winters and short, cool summers. In a review of the literature, de Groot and others [21] state that the optimum temperature for photosynthesis in dwarf birch is 50 to 55 °F (10-13 °C). Dwarf birch appears to tolerate colder temperatures than bog birch. Annual precipitation across the range of dwarf birch varies from 12 to 16 inches (300-400 mm) in circumpolar regions to 47 to 78 inches (1,200-2,000 mm) in the British Isles.
SUCCESSIONAL STATUS:The phenology of dwarf birch across its range is summarized below.
Seasonal development of dwarf birch [23] | |
bud break | mid-May to mid-June |
new shoot growth | mid-June to early August |
female catkins in flower | early June |
seeds ripe | August |
leave senescence | August-September |
leaf abscission | complete by late September |
In tussock tundra in central Alaska, dwarf birch leaves expand in June, mature in mid-July, and begin to senesce in early August [65]. Flowering and fruiting dates are given below.
Timing of flowering and fruiting in dwarf birch in central Alaska [65] | ||
Onset of flower bud swell | Onset of flowering |
Onset of fruiting |
28 May-15 July | 17 June-31 July | 9 July-17 July |
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 [22,24]. Black spruce-birch (Betula spp.) is the most widespread forest type in interior Alaska and also the type with the highest frequency of fire [91]. Native Americans were an important cause of fires in the black spruce-birch ecosystem [59]. Fire frequency increased with the increase in mining activity in the 1800s [89]. Today, most fires are lightning caused [39,58]. Between 1940 and 1969, lightning was responsible for 78% of the area burned in interior Alaska [89].
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 [32,89]. Fires can occur, however, whenever fuels are not covered with snow and are exposed to sufficiently warm temperatures and drying winds [89].
Fire years are sporadic in occurrence but tend to occur at least once every decade [40]. “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 [93]. The average acreage burned each year in interior Alaska is approximately 1 million acres [59]. Fires tend to be large and may spread over thousands to hundreds of thousands of acres or more [40,57,87].
Estimated fire-return intervals in the black spruce-birch ecosystem vary from 50 to 200 years [40,93]. Fires occur every 50 to 70 years in black spruce-white spruce/bog birch/reindeer lichen communities in interior Alaska [32]. Heinselman [40] 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 [2,60].
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 [57,58,90]. There is often nearly continuous fuel from the forest floor to the tree crowns [93]. 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 [26,40,87,93].
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 [82] |
tamarack | Larix laricina | 35-200 [68] |
black spruce | Picea mariana | 35-200 |
conifer bog* | Picea mariana-Larix laricina | 35-200 |
jack pine | Pinus banksiana | <35 to 200 [19,26] |
aspen-birch | Populus tremuloides-Betula papyrifera | 35-200 [26,94] |
The few studies that address the effects of fire on dwarf birch have shown that dwarf birch may either increase or decrease after fire. In the Kenai Mountains, Alaska, prescribed burning was conducted at 17 sites between 1979 and 1984. In postfire surveys conducted in 1998 and 1999, dwarf birch cover had increased by an average of 2% across the burns. In 10 burns there was no change; in 1 burn there was a 4% decrease in dwarf birch cover; and in 6 burns there was an increase in dwarf birch cover that ranged from 1% to 10% [9]. Dwarf birch also increased after a July 1977 tundra fire on the Seward Peninsula, Alaska [73].
Percent frequency (and cover) of dwarf birch at 3 postfire successional stages [73] | |||
postfire year 1 | postfire year 3 | postfire year 24 | |
Site 1 | 40 (1) | 60 (1) | 100 (7) |
Site 2 | trace (0) | trace (0) | 3 (10) |
Site 3 | trace (0) | trace (0) | 6 (20) |
Site 4 | 40 (trace | 60 (trace) | 80 (11) |
Site 5 | 40 (1 | 50 (1) | 60 (6) |
In other studies in similar habitats, dwarf birch decreased after fire. In tussock tundra northwest of Fairbanks, Alaska, production of leaves and buds in dwarf birch was significantly less in burned tundra than in unburned tundra both 1 year after fire (P<0.05) and 13 years after fire (P<0.01) [30].
Dwarf birch production (g/m²) in burned and unburned tundra 1 and 13 years after fire [30] | ||
Burned | Unburned | |
1970 (postfire year 1) | 1.0 | 4.8 |
1982 (postfire year 13) | 10.8 | 21.2 |
Dwarf birch frequency was greater in unburned than in burned tundra sites 1 year after a July 1977 wildfire on the Seward Peninsula. Frequency of dwarf birch measured in May and June 1978 is given below [99].
Dwarf birch frequency (%) in burned and unburned stands 1 year after fire [99] | ||
Burned | Unburned | |
late May | 3 | 87 |
mid-June | 8 | 80 |
Ptarmigan eat the buds, catkins and twigs of dwarf birch in Alaska. Dwarf birch and bog 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 [96]. Spruce grouse eat dwarf birch seeds in central Alaska [96].
Dwarf birch foliage provides forage for a number of herbivorous insects. In Alaska, the total number of herbivorous insects decreases 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 in Koponen [51].
Palatability/nutritional value: Carbohydrate concentrations are high in dwarf birch stems and roots in the spring and decline with shoot and root growth. Carbohydrates increase again in the fall and are stored in roots and stems during the winter [14]. Protein content in dwarf birch foliage on the Kenai Peninsula, Alaska, ranges from 7.1% to 16.8%. Nutrient content of dwarf birch stems and leaves collected over 2 summers on the Kenai Peninsula is provided in the table below [67].
Nutrient content (ppm) of dwarf birch stems and leaves [67] | |||||||
Ca | K | Mg | Na | Cu | Fe | Mn | Zn |
631-3,920 | 5503-5,550 | 646-1,730 | 55-74 | 11-15 | 61-86 | 5-109 | 45-64 |
Dwarf birch produces carbon- and nitrogen-based antiherbivore compounds that deter browsing [21].
Cover value: No information is available on this topic.
VALUE FOR REHABILITATION OF DISTURBED SITES:Information on dwarf birch cultivars is available in Santamour and McArdle [75].
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