SPECIES: Ledum palustre


Ledum palustre: INTRODUCTORY

INTRODUCTORY

SPECIES: Ledum palustre

© 2005 Susan Aiken, Canadian Museum of Nature


AUTHORSHIP AND CITATION:
Gucker, Corey L. 2005. Ledum palustre. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

FEIS ABBREVIATION:
LEDPAL

SYNONYMS:
Ledum palustre ssp. decumbens (Ait.) Hult. [37]
    = Ledum decumbens (Ait.) Lodd. [2,71]

NRCS PLANT CODE [78]:
LEPA11

COMMON NAMES:
northern Labrador tea
marsh Labrador tea
narrow-leaf Labrador tea

TAXONOMY:
The currently accepted scientific name of northern Labrador tea is Ledum palustre (Ait.) Hult. (Ericaceae) [37,39]. A single subspecies, L. palustre ssp. decumbens (Ait.) Hult. is recognized [37]. In this review, the subspecies is not distinguished. In this species review, northern Labrador tea will refer to both L. palustre and L. p. ssp. decumbens. For any information cited that recognizes the Ledum genus alone, the common name, Labrador tea, will be used.

LIFE FORM:
Shrub

FEDERAL LEGAL STATUS:
None

OTHER STATUS:
Northern Labrador tea is considered rare in British Columbia, Ontario [63], and Saskatchewan [39].

DISTRIBUTION AND OCCURRENCE

SPECIES: Ledum palustre
GENERAL DISTRIBUTION:
Northern Labrador tea is restricted to northern latitudes. In the western hemisphere, northern Labrador tea occurs in Alaska and Canada [39]. Northern Labrador tea occupies a large range in Alaska and in Canada's Yukon, Northwest, and Nunavut territories. Distribution of northern Labrador tea is restricted to the northern parts of Canada's more southern territories and is likely absent from Prince Edward Island, Nova Scotia, and New Brunswick. Populations of northern Labrador tea are considered rare in British Columbia, Ontario [63], and Saskatchewan [39]. In northern Ontario, northern Labrador tea has expanded its range but is still regionally restricted [62].

Plants database provides a distributional map of northern Labrador tea.

ECOSYSTEMS [29]:
None

STATES/PROVINCES: (key to state/province abbreviations)
UNITED STATES
AK

CANADA
AB BC MB NF NT
NU ON PQ SK YK

BLM PHYSIOGRAPHIC REGIONS [4]:
None

KUCHLER [41] PLANT ASSOCIATIONS:
None

SAF COVER TYPES [25]:
12 Black spruce
13 Black spruce-tamarack
16 Aspen
18 Paper birch
107 White spruce
201 White spruce
202 White spruce-paper birch
204 Black spruce
217 Aspen
251 White spruce-aspen
252 Paper birch
253 Black spruce-white spruce
254 Black spruce-paper birch

SRM (RANGELAND) COVER TYPES [69]:
ALASKAN RANGELANDS
901 Alder
904 Black spruce-lichen
906 Broadleaf forest
911 Lichen tundra
912 Low scrub shrub birch-ericaceous
913 Low scrub swamp
916 Sedge-shrub tundra
918 Tussock tundra
920 White spruce-paper birch
921 Willow

HABITAT TYPES AND PLANT COMMUNITIES:
Bliss [5] describes several generic arctic and subarctic vegetation types in which northern Labrador tea is important. In low shrub tundra, northern Labrador tea is common where the open shrub canopy is characterized by the presence of low-growing (16-24 inches (40-60 cm)) dwarf birch (Betula nana), grayleaf willow (Salix glauca var. acutifolia), diamondleaf willow (S. pulchra), and Richardson willow (S. richardsonii). In dwarf shrub heath tundra, northern Labrador tea and other evergreen species belonging to the Ericaceae, Empetraceae, and Diapensiaceae families are the dominant woody vegetation. Northern Labrador tea is least common in tall shrub tundra vegetation occurring along rivers and near lakes. Tall shrub tundra vegetation occupies more nutrient rich sites than other tundra types. Dominant species in tall shrub tundra include willows (Salix spp.), birches (Betula spp.), and alders (Alnus spp.).

Alaska: Northern Labrador tea occurs in arctic and subarctic vegetation in the interior and coastal regions of Alaska. In the foothills of the Brooks range, approximately equal proportions of northern Labrador tea, sheathed cottonsedge (Eriophorum vaginatum), dwarf birch, and mountain cranberry (Vaccinium vitis-idaea) dominate the tussock tundra vegetation of the landscape [13].

In many northwestern Alaska vegetation types, northern Labrador tea is considered important. The birch-willow vegetation type includes bog birch (B. glandulosa), dwarf birch, diamondleaf willow, Richardson willow, and Alaska bog willow (S. fuscescens). The dwarf birch-heath/lichen vegetation type occupying rocky slopes with well-drained soils is typical habitat for dwarf birch, bog blueberry (V. uliginosum), black crowberry (Empetrum nigrum), and northern Labrador tea. The blueberry (Vaccinium spp.)-heath/lichen vegetation is widespread on hills of the Seward Peninsula. Bog blueberry dominates this community type but northern Labrador tea and scattered low growing dwarf birch are common too. The white arctic mountain heather (Cassiope tetragona)-blueberry and alpine bearberry (Arctostaphylos alpina)-mountain cranberry vegetation types are also northern Labrador tea habitat. The alpine bearberry-mountain cranberry type occupies gravelly sites of the Cape Nome headland. In the dwarf shrub-marsh community type, northern Labrador tea occurs with several characteristic bog species including cloudberry (Rubus chamaemorus), bog cranberry (V. oxycoccos), and sedges (Carex spp.). The cloudberry-dwarf shrub marsh vegetation type includes mountain cranberry, dwarf birch, black crowberry, cloudberry, and northern Labrador tea [32].

In the Yukon-Tanana uplands of Alaska, northern Labrador tea has 40% cover in black spruce/cottongrass (Picea mariana/Eriophorum spp.) communities that occur next to streambank vegetation. There is often standing water between the tussocks [22]. In sheathed cottonsedge-dominated communities near Fairbanks, northern Labrador tea, bog blueberry, mountain cranberry, willow, dwarf birch, bog birch, and cloudberry can all occur [10]. Northern Labrador tea also occurs in the following young forest community types found in the interior of Alaska: quaking aspen/russet buffaloberry (Populus tremuloides/Shepherdia canadensis), paper birch (B. papyrifera)-quaking aspen/highbush cranberry (Viburnum edule), paper birch-quaking aspen/mountain alder (Alnus viridis ssp. crispa), and white spruce (Picea glauca)-paper birch/mountain-fern moss (Hylocomium splendens) [91].

On wet coastal plains of Alaska, Bliss [5] recognizes northern Labrador tea in cottongrass-dwarf shrub heath tundra vegetation. Northern Labrador tea has 50% constancy and 3% cover in the early to mid-successional beach strawberry (Fragaria chiloensis) community type that occurs on barrier islands and coastal dunes of Alaska's Copper River Delta. Here the soils are well-drained, silt sands with pH levels near 6.4 [7]. On the Kenai Peninsula, northern Labrador tea occurs with 50% constancy in the white spruce-black spruce/black crowberry-mountain cranberry/felt lichen (Peltigera spp.)-big red stem moss (Pleurozium spp.) community type [61].

Northwest Territories: Northern Labrador tea occurs in white spruce forests of the Mackenzie Delta region of Canada's Northwest Territories. Here white spruce trees are small, under 13 feet (4 m) tall, and widely spaced. Hummocks are covered by reindeer and cup lichens (Cladina and Cladonia spp.), and the shrub layer is dominated by willow, bog birch, and northern Labrador tea. Most of these communities are even-aged postfire forests. Northern Labrador tea is typical vegetation in sedge tundra that occurs on the Yukon coastal plain and the unglaciated tip of the Tuktoyaktuk Peninsula. Shrub tundra vegetation of the Mackenzie Delta includes grayleaf willow, bog birch, alder, Lapland rosebay (Rhododendron lapponicum), and white arctic mountain heather [47].

Yukon: Northern Labrador tea is a dominant species in several community types of the Yukon region. In the sheathed cottonsedge-northern Labrador tea-dwarf birch vegetation type, northern Labrador tea has 22.5% cover. This type is very similar to the tussock-sedge tundra community. The alpine bearberry-sheathed cottonsedge-northern Labrador tea community closely resembles dwarf shrub tundra vegetation. Some scattered black spruce trees may occur in this type where northern Labrador tea coverage averages 21.5%. In the lichen/bog birch/northern Labrador tea community type that is similar to lichen/shrub or alpine tundra types, northern Labrador tea community coverage averages 22.3%. Occasional stunted black and/or white spruce occupy this habitat that is typical on open, steep north-facing slopes in the Ogilvie Mountains. The black spruce-bog birch/northern Labrador tea community type typically supports northern Labrador tea coverages of approximately 20%. This type is also known as a spruce-tall shrub taiga type and occurs on tundra peat soils on gentle northeast or northern facing slopes of the Eagle Plains and Richardson Mountains. Black spruce/lichen/northern Labrador tea communities occupy flat to gentle slopes with western and southwestern exposures. This type is also referred to as the lichen/spruce taiga type [72].

Other northern Labrador tea community types include the following (listed in order of decreasing northern Labrador tea coverage): mountain alder-alpine bearberry-bog blueberry, netleaf willow (Salix reticulata)-dwarf birch-cloudberry, cloudberry/bog birch/bog blueberry, black spruce/sheathed cottonsedge-sedge, black spruce/bog blueberry/tamarack (Larix laricina), white spruce-paper birch/mountain cranberry on steep south slopes, and lichen/white arctic mountain heather/arrowleaf sweet coltsfoot (Petasites sagittatus) [72].

Northern Labrador tea is recognized as a dominant species in the following vegetation classification:
Yukon, Canada: [72]


BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Ledum palustre

© 2005 Susan Aiken, Canadian Museum of Nature

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 [1,37,81].

Northern Labrador tea is a long-lived, resinous, evergreen shrub [8,37]. This multi-branched, prostrate shrub grows 4 to 24 inches (10-60 cm) tall and is capable of clonal growth through layering [1,2,8,71,81]. Northern Labrador tea has alternate linear leaves. The small, thick, linear leaves have a leathery appearance and are often 5 to 8 times long as they are wide. The upper leaf surface is shiny and glabrous, while the lower surface is densely hairy [1,2,37,71,81]. The margins of the leaves bend underneath to give a rounded appearance [63]. Northern Labrador tea flowers are fragrant umbels [37,81]. The fruit is a 5-parted capsule measuring 2 to 3.5 mm long by 1 to 3.5 mm wide and opening at the base [81]. Numerous small (1.7×0.3 mm) seeds are produced [1,38].

Growth dynamics: Northern Labrador tea grows in harsh arctic and subarctic environments and has prompted many to investigate its above- and below-ground growth dynamics. In the Atkasook study area southwest of Barrow, Alaska, researchers found that northern Labrador tea had less than 50% of its biomass underground and that leaves constituted almost 50% of its aboveground biomass. Northern Labrador tea maintains low nutrient levels, and soil nutrients are slowly transferred into the leaves throughout the growing season where they are stored through the winter [12].

In Eagle Creek, northeast of Fairbanks, Alaska, the underground structures of 100 northern Labrador tea plants revealed that northern Labrador tea's fine roots averaged 0.12 mm in diameter but ranged from 0.03 to 0.57 mm. From a sample size of 5, researchers estimated that northern Labrador tea root extension averaged 67 m/g. From aboveground and belowground measurements of 8 northern Labrador tea plants, researchers found that the mean fine root to leaf dry weight and fine root surface to leaf area ratios were 0.3 and 2.03, respectively [42].

Northern Labrador tea woody stem production and turnover investigations were made in Eagle Creek (1978) and Toolik Lake (1982-83), Alaska. In tussock tundra of Eagle Creek, the growth rate of 1- to 15- year-old northern Labrador tea plants was 15.4% per year. The relative secondary growth rate of 15-year-old ramets was 8% annually in moist tussock tundra of arctic Alaska [8]. In Toolik Lake, production and turnover of woody materials was compared in tussock tundra and evergreen heath communities. In the tussock tundra, the growth rate for 1- to 20-year-old northern Labrador tea plants was 14.4% per year. In low-productivity, low-biomass evergreen heath vegetation, the 1- to 20- year-old growth rate was 8.9% annually. The turnover rate of nutrients and woody stem biomass was longer in evergreen heath communities as was the life expectancy of stems. The turnover rates and life expectancies of northern Labrador tea stems are summarized below for 2 vegetation types of Toolik Lake [68].

Vegetation type Biomass turnover (yr) Nitrogen turnover (yr) Phosphorus turnover (yr) Stem life expectancy (yr)
Tussock tundra 7.9 10 11.1 6.1
Evergreen heath 11.5 12.8 12.7 6.6

RAUNKIAER [59] LIFE FORM:
Chamaephyte

REGENERATION PROCESSES:
Northern Labrador tea reproduces through seed production [49] and vegetative sprouting [16,57]. The literature suggests that asexual regeneration predominates following disturbances, but sexual reproduction is important in maintaining viability in undisturbed communities.

Breeding system: No information is available on this topic.

Pollination: The pollination of northern Labrador tea flowers was not addressed specifically in the literature. However, northern Labrador tea reportedly has nectaries and is likely visited by insects [1].

Seed production: A "large" number of seeds (>50) are produced per northern Labrador tea flower [38]. In tussock tundra vegetation of Eagle Creek, Alaska, researchers reported that northern Labrador tea produced numerous very light seeds. However, just 33% were viable. Northern Labrador tea typically aborted seeds sometime between the time of fruit formation and seed dispersal. The table below summarizes the average flower, fruit, and seed production by northern Labrador tea in Eagle Creek. Observations coincided with what was considered a year of high flower production in the area [15].

Number of growing points*/m² 221
Number of flowers/m² 38
Number of flowers/100 growing points 11
Number of fruits/m² 34
Mortality (proportion of flowers that did not produce fruit) 0.25
Number of full seeds/fruit 58
Proportion of viable seeds 0.33
Number of viable seeds/m² 650
Number of viable seeds/100 growing points 295
*Growing points were defined as active apical meristem tissue that was producing leaves, stems, or flowers.

From the values presented above, researchers calculated the percentage of total annual production that northern Labrador tea allocated to vegetative growth and reproductive effort. Sexual reproductive effort was 3.4% of northern Labrador tea's annual production, while vegetative growth was 95.6% [15].

Vegetative growth 95.6%
Flowers 0.8%
Fruit 2.6%
Total sexual reproductive effort¹ 3.4%
Viable seed reproductive effort² 0.14%
Reproductive efficiencies³ 4.1%
¹Flower and fruit production/annual above-ground production (sexual and vegetative).
²Viable seed production/annual above-ground production (sexual and vegetative).
³Viable seed production/total sexual reproductive effort².

Seed dispersal: Northern Labrador tea seed is wind dispersed [15,18].

Seed banking: McGraw [48] suggests that northern Labrador tea seed has little dormancy, and while it may last in the soil for more than a single growing season, it is not viable once buried below the 1st substrate layer. In tussock tundra of Eagle Creek, Alaska, 40 soil samples taken from cores with 2 inch (5 cm) diameters at a maximum depth of 14 inches (35 cm) were collected on August 12, 1978. Vertical structure was maintained, and samples were stored at 1°F (-17 °C) for 4 months. On January 19, 1979, germination of the soil seed bank was encouraged under greenhouse conditions. Greenhouses received 20 hours of daylight, 4 hours of darkness, and an average daily temperature of 68 °F (20 °C). A total of 1,295±301 (s x) northern Labrador tea seeds/m² germinated. Most (90%) came from the top 2 inches (5 cm) of soil [48].

From soil samples (15×15×10 cm) collected in 4 undisturbed tundra communities of northern Alaska, no northern Labrador tea seedlings emerged under greenhouse conditions regardless of stratification. Sample collections occurred on July 23, 1981 and July 15, 1983, which is likely prior to northern Labrador tea seed dispersal [24].

Germination: Northern Labrador tea seed must be near the soil surface to germinate and germinates better given long day conditions. Cotyledons turn green prior to radicle extension inside the transparent seed coat. Ninety-four percent of northern Labrador tea seed collected in August of 1977 from the Mackenzie Delta of the Northwest Territories germinated. Seed did not require stratification [38].

Experiments conducted under controlled and natural conditions suggest that day length and soil temperature are also important factors in controlling northern Labrador tea germination. Seed was collected at the time of seed shed from the upper Dietrich River Valley in the Brooks Range. Unstratified seed germination was low at 50 °F (10 °C), 59 °F (15 °C), and 68 °F (20 °C) when subjected to short day lengths (13 hours of light). Cold stratification and long day treatments increased the percent germination and encouraged seed to germinate in even 41 °F (5 °C) temperatures. Seeds sown in natural settings on September 4 had not germinated by June 4, but seedlings did appear by June 16 when soils temperatures were greater than 41 °F (5 °C). This study suggests that day length may be important in maintaining northern Labrador tea seed dormancy after seeds are shed [18].

Seedling establishment/growth: Seedling growth is "exceedingly slow" for northern Labrador tea. Establishment of seedlings was studied in undisturbed tussock tundra near Eagle Creek, Alaska. From 40 sampled plots, 181±36 (s x) seedlings/m² emerged. Mortality was 77% per year during the first 3 years of seedling growth. After this period mortality decreased to between 5% and 15% annually. Even with these high rates of mortality, researchers maintained that "enough seedlings pass through the 1st high mortality establishment phase to contribute to the undisturbed vegetation community." Most northern Labrador tea seedlings germinated on dead leaves and dicranum moss (Dicranum spp.). Seedling growth is slow, and seedlings over 20 years old may still have juvenile leaves [49].

Asexual regeneration: Asexual reproduction likely predominates following disturbances that top-kill northern Labrador tea. The 1944 to 1953 oil exploration in northern Alaska left debris abandoned on the tundra surface that was cleaned up in the late 1970s and early 1980s. Recovery of the debris resulted in bare sites that were monitored 2 and 4 years following removal. Northern Labrador tea vegetatively colonized some of the driest sites sampled. Frequency after debris removal was 1% and coverage was 3%. There were no northern Labrador tea seedlings [23].

SITE CHARACTERISTICS:
Northern Labrador tea's slow growth rate and slow rate of nutrient, stem, and leaf turnover make it successful in low nutrient environments [13]. It occupies wet and dry habitats in subarctic and arctic areas. Northern Labrador tea occurs with other heaths in dry, rocky areas that span the entire state of Alaska [37]. It occupies sedge tussocks and wet depressions of arctic tundra and sphagnum bogs and wet black spruce vegetation types of boreal forests [81]. Northern Labrador tea is also described in muskegs and alpine areas from Newfoundland to the Aleutian Islands [2]. Dry areas and upper levels of stream banks in the Canadian Arctic Archipelago also provide northern Labrador tea habitat [1].

Soils: Northern Labrador tea habitats occur on dry to imperfectly drained soils that are acidic and underlain with a permafrost layer. In arctic environments, just the upper 8 to 24 inches (20-60 cm) of soil thaws in the summer; along rivers and lakes, soils may thaw to a depth of 79 inches (200 cm) [5]. On the barrier islands and coastal dunes of Alaska's Copper River Delta, soils are well-drained, silt sands and the pH of the mineral soils averages 6.4 [7]. The tussock tundra of the Imnavait Creek Watershed at the foothills of the central Brooks Range has poorly drained soils. A poorly developed mineral horizon with a pH of 5.5 overlays organic and permafrost layers ([53] cites others). In the black spruce/sheathed cottonsedge vegetation of the Yukon-Tanana Uplands of Alaska, northern Labrador tea has 40% cover on sites where there is standing water between the tussocks [22].

Substantial information was gathered on the soils of Yukon habitats in which northern Labrador tea dominates. This information is summarized below [72]:

Community type Depth to permafrost (cm) pH
sheathed cottonsedge/northern Labrador tea/dwarf birch 30-60 3.3-4.9
Alpine bearberry/sheathed cottonsedge/northern Labrador tea 39-55 3.4-3.9
Lichen/bog birch/northern Labrador tea 30-55 3.5-5.9
Black spruce/bog birch/northern Labrador tea 45-65 ----
Black spruce/lichen/northern Labrador tea 100-150 2.8-3.8

Elevation: Very little was reported on northern Labrador tea's elevation range. Hulten [37] suggests that northern Labrador tea occurs at elevations up to 5,905 feet (1,800 m) throughout Alaska.

Climate: Northern Labrador tea grows in harsh subarctic and arctic climates [63]. Near Barrow, Alaska, where northern Labrador tea grows in tussock tundra habitats, the growing season lasts an average of 75 days from mid-June to late August. The average July temperature in 1975 was 45 °F (7.2 °C), and mean precipitation for the summer season was 3.2 inches (80 mm) [12]. Northern Labrador tea also grows in the foothills of the central Brooks Range of Alaska. This area experiences severely cold winters, cool summers, little precipitation, and continuous winds (rarely exceeding 17 m/s). During a 1986 study, annual precipitation measured 13.5 inches (344 mm) with almost equal proportions of rain and snow. The minimum temperature for the year was -45 °F (-43 °C), and the maximum was 66 °F (19 °C) [53]. Tundra vegetation on the northwestern shore of Hudson Bay has just a 6-week growing season, experiences frost at any time, and reaches a mean temperature of 50°F (10 °F) during the warmest month [17].

A study done in central northern Canada found that northern Labrador tea was strongly correlated (r =0.56-0.68) with arctic air masses in white spruce communities and Pacific air masses in rock field tundra communities. The author suggested that northern Labrador tea's conflicted correlations may be due to a wide tolerance of a variety of harsh conditions or may be due to some ideal adaptation to each site [44].

Starr and Oberbauer [73] found that northern Labrador tea was able to photosynthesize at low rates when covered with less than 12 inches (30 cm) of snow. This finding suggests a keen adaptation to growth in arctic conditions. Researchers reported that photosynthetic rates increased with decreasing snow depth.

SUCCESSIONAL STATUS:
Northern Labrador tea is a shade intolerant species [63] that occurs predominantly in late-seral communities undergoing primary succession. However, following disturbances in areas where northern Labrador tea is established, this species rapidly recolonizes the site.

Shade relationships: The findings following a fire in black spruce forests near Fairbanks, Alaska, indicated that northern Labrador tea preferred open canopies to densely shaded conditions. Northern Labrador tea coverage on burned sites immediately following the fire was 0.6%, and 3 years after the fire was 9.3%. On similar unburned sites, the coverage of northern Labrador tea was 13.8% on open-canopy sites with low black spruce cover but was 2.5% on sites with very dense black spruce coverage [88].

General successional change: Assigning northern Labrador tea to a single successional stage is difficult since this species is associated with a wide variety of vegetation types that experience different successional changes. In the taiga, northern Labrador tea occurs in all seral stages but is highly prominent in mature vegetation types [14]. In the beach strawberry community type that occupies the barrier islands and coastal dunes of Alaska's Copper River Delta, northern Labrador tea occurs with 50% constancy. This community is considered an early- or mid-seral type [7]. In the Mackenzie Delta of the Northwest Territories, northern Labrador tea occurs in white spruce forests with trees aged 400 years or older. Here tree cover is sparse (10%) and white spruce tree seedlings are absent [54].

Northern Labrador tea appears in intermediate stages of primary bog succession. This process begins with open water that is colonized by immersed sedges and mosses which reproduce and multiply forming dense mats of vegetation. These mats are later colonized by shrubs species such as northern Labrador tea. Finally, black spruce trees colonize the area. A time table for this process was not provided [19].

In a study of forest succession along the Chena River north of Fairbanks, Alaska, researchers compared vegetation at different developmental stages. Sampling occurred in 15-year-old willow stands on an open gravel bar, 50-year-old balsam poplar stands, 120-year-old white spruce stands, 120-year-old white spruce/black spruce stands, and 120-year-old black spruce-dominated stands. The 120-year-old black spruce stands represented climax vegetation for the area. Northern Labrador tea occurred only in climax black spruce vegetation [80].

Response to disturbance: Bliss [5] describes arctic succession following disturbances as a shift in species' coverage rather than a change in species over time. In arctic tundra and boreal forests recovering from disturbances, northern Labrador tea often occurs in early-, mid-, and late-seral vegetation.

In tundra vegetation north of the treeline in the Yukon territory, researchers compared the average coverage of northern Labrador tea on undisturbed sites, in vehicle tracks, and in drainage ditch sites. The percent coverage on undisturbed sites was significantly greater (p>0.01) than on disturbed sites. However, the authors note that drainage ditches had standing water all growing season, and the vehicle tracks had pooled water in the early spring and summer months. Whether or not this affected northern Labrador tea growth is unknown. The largest factor contributing to northern Labrador tea's coverage, disturbance or standing water, is undeterminable [86].

When researchers removed all the vegetation and rhizomes in 6.6×6.6 foot (2×2 m) sections of tussock tundra near Eagle Creek, Alaska, northern Labrador tea did not recolonize cleared sites by the 2nd postdisturbance year. The predisturbance vegetation was a mix of sheathed cottonsedge, northern Labrador tea, bog blueberry, mountain cranberry, and Bigelow sedge (Carex bigelowii). The removal of northern Labrador tea's underground structures delayed colonization. Northern Labrador tea may take longer than 2 years to colonize bare sites through sexual reproduction [16].

While northern Labrador tea is not a palatable shrub browsed by arctic mammals, the following study likely involved trampling effects and browsing on northern Labrador tea. On Rideout Island of the Northwest Territories, 500 to 1,000 caribou became stranded in the summer of 1987. The 15 square mile (40 km²) island could not sustain the caribou, and all died of malnutrition after severely grazing island vegetation. Researchers visited the island in late July, 1988, and compared the island vegetation to similar mainland communities. Coverage of northern Labrador tea was significantly lower in the low shrub tundra on the island due to trampling and/or browsing. Findings from the study are summarized below [33].

Island Mainland
Cover (%) in low shrub tundra 2±1 7±2*
Cover (%) in tussock tundra 6±2 4
Mean % of browsed shoots
(both communities)
5±3
(n=8)
0
(n=4)
*significant (p<0.05)

The study of disturbed sites in the Tuktoyaktuk Peninsula of the Northwest Territories revealed that northern Labrador tea is sensitive to soil surface disturbances. A comparison of disturbed and undisturbed sites showed that northern Labrador tea coverage is reduced on disturbed sites regardless of when roads, trails, and seismic lines are used [34].

Northern Labrador tea does show some resistance to chemical disturbances, however. When sites in the western Canadian arctic were treated with oil (0-1.5 cm) in late June, northern Labrador tea regrowth was evident by August of the same year [6].

The fire effects section provides additional information regarding northern Labrador tea and secondary succession.

SEASONAL DEVELOPMENT:
Summer flowers and fall fruits are typical for northern Labrador tea. In Alaska, flowers appear in June and early July, fruits mature by July or August, seeds are released in the fall, but capsules may remain attached through the winter [81]. More specific dates regarding northern Labrador tea's seasonal development in tussock tundra of central Alaska are provided by Murray and Miller [52]. Between May 31 and June 13 flower buds swell, between June 27 and July 3 flowering is initiated, from July 9 through July 21 fruits are set, and after August 28 seeds are dispersed. In arctic and subarctic regions of Canada, flowers are possible anytime June through August, and seeds mature in the fall [63].


FIRE ECOLOGY

SPECIES: Ledum palustre  
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Northern Labrador tea survives fires by sprouting from underground roots [57]. Sprouting occurs rapidly following fire [5].

Fire regimes: Fires in northern Labrador tea habitats are common. Likely the fire return interval is shorter in shrub and tussock tundra vegetation than in boreal forests. Bliss and Wein [6] consider "tundra fires less damaging than forest fires because the amount of combustible materials is less, and cool wet soils usually prevent deep burning."

Arctic fire ecology: Fires in arctic lichen/heath/moss communities burn irregularly. The slowly accumulated litter beneath northern Labrador tea plants together with its resinous leaves and stems causes northern Labrador tea to "burn fiercely." Blackened circles around northern Labrador tea plants are common [17]. Bliss [5] considers dwarf shrub heath and low shrub tundra the most common vegetation types burned in arctic fires. Fires in tundra vegetation serve several functions. The darkened soil surfaces can increase the depth of thaw by 30% to 50%, and nutrient release is important in these low-nutrient, slow-turnover systems [5]. In tussock tundra vegetation of Alaska's Seward Peninsula, the evidence of fire is virtually undetectable after 7 years. Studies indicate that just the relative proportions of species change [55].

Boreal/taiga fire ecology: Canadian boreal forests burned "extensively and repeatedly" [67]. Rowe and others [64] describe several factors contributing to the likelihood of fires. Lightning is common from June through August, summers are dry and warm, and long periods of daylight easily dry surface fuels. Mosses and lichens occupy large surface areas and dry out rapidly. In terms of boreal and subarctic regions, Rowe and others [64] assert that the question should not be whether these sites burned but when and how often. Fire is also considered important to energy cycling. Energy conversion together with selected fire regeneration traits is important to maintaining the "stability and viability" of boreal forests [67].

Studies of succession in upland taiga vegetation of Riley Creek in Denali National Park, Alaska, suggest a fire return interval of 40 to 60 years before the fire suppression era. Researchers suggest that "plants emerging from underground parts immediately after the last fire are typically the same individuals whose above ground biomass will support the next fire" [46].

In white spruce forests of the Mackenzie Delta region of Canada's Northwest territories, the fire return interval is likely longer than that of Denali's upland taiga. Most of these forests are even-aged postfire communities with widely-spaced, small white spruce trees under 13 feet (4 m) tall. Following fires in this vegetation type, shrubs return after 15 years, while trees take between 100 and 150 years to re-establish [47].

In peat plateaus, fire is common due to well-drained sites, an abundance of flammable fuels, black spruce trees with branches near ground, resinous shrubs such as Labrador tea, and quickly-dried surface fuels [64].

The following table provides fire return intervals for plant communities and ecosystems where northern Labrador tea is important. For further information, see the FEIS review of the dominant species listed below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
black spruce Picea mariana 35-200
conifer bog* Picea mariana-Larix laricina 35-200 [21]
aspen-birch Populus tremuloides-Betula papyrifera 35-200 [21,82]
quaking aspen (west of the Great Plains) Populus tremuloides 7-120 [3,30,50]
*fire return interval varies widely; trends in variation are noted in the species review

POSTFIRE REGENERATION STRATEGY [74]:
Small shrub, adventitious bud/root crown
Ground residual colonizer (on-site, initial community)


FIRE EFFECTS

SPECIES: Ledum palustre
IMMEDIATE FIRE EFFECT ON PLANT:
Northern Labrador tea's resinous leaves, stems, and accumulated litter cause this species to "burn fiercely" [17]. Northern Labrador tea is top-killed by fire but underground structures survive [67].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
No additional information is available on this topic.

PLANT RESPONSE TO FIRE:
Northern Labrador tea re-establishes on burned sites through root sprouts [5,57,67]. Chapin and Van Cleve [14] suggest that northern Labrador tea has "spotty" survival following fires in the taiga. Northern Labrador tea is rooted in the organic horizon and survives in patches of organic matter that are not totally consumed by fire. Researchers consider northern Labrador tea an important understory species throughout succession.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Following fire, northern Labrador tea initially decreases in coverage and frequency. However, northern Labrador tea is often noted as an important or conspicuous species immediately following fires in tussock tundra, shrub tundra, and boreal forests. Likely fire severity and/or depth of burn dictate the time required for northern Labrador tea to regain prefire coverage and frequency.

Early postfire effects: The following studies highlight early northern Labrador tea postfire responses. In most cases, the re-emergence of northern Labrador tea is rapid. Following a June fire in stunted black spruce-dominated taiga of northwestern Manitoba, northern Labrador tea growth was common in the 1st postfire year. All upland vegetation was top-killed and mosses burned 4 inches (10 cm) deep in spots following this fire [51]. Wein [83,84] considered northern Labrador tea's importance to be greater after tundra and forest tundra fires in northern Canada. In Alaska and Inuvik, northern Labrador tea and sheathed cottonsedge had the most growth in the 1st postfire year following fires that removed litter and charred tussocks [6]. Of 4 sites burned in 1970 in north-central Saskatchewan, 2 supported dense Labrador tea growth by 1973. Fire severity was not described [51].

Following the Wickersham fire that burned black spruce forests near Fairbanks, Alaska, in late June, 1971, researchers measured vegetation and environmental changes. Sites burned "lightly" and "heavily" were compared to unburned sites. "Lightly" burned sites had less than 50% of the ground blackened with tree branches and crowns scorched but not consumed. "Heavily" burned sites had more than 90% of the ground surface blackened and tree crowns consumed. All burned sites had greater depths and rates of thaw in the 1st postfire year than did unburned sites. The snow-free period was 126 days on burned sites and 119 on unburned sites. Maximum soil temperatures at 4 inches (10 cm) were 51 °F (10.5 °C) reached by July 30 on burned sites and 43 °F (6 °C) reached by September 13 on unburned sites. Northern Labrador tea density and frequency were much lower on the heavily burned sites, and control levels were not reached by the 3rd postfire year on either burned site. Results from the study are given below [79].

Fire type Control "Heavy" "Light"
Year mean 1971 1972 1973 1974 1971 1972 1973 1974
Density (stems/ha) 3.1 0 0 0.05 0.15 1.45 1.05 1.9 1.3
Frequency (%) 65 0 0 5 10 25 35 65 40

In an additional study of sites burned by the Wickersham fire, Wolff [88] found that northern Labrador tea coverage on burned sites immediately following the fire was 0.6%, and 3 years later coverage was 9.3%. On similar unburned sites, the coverage of northern Labrador tea was 13.8% on open-canopy sites with low black spruce cover and 2.5% on sites densely covered by black spruce.

A lightning-caused fire burned 386 mi2 (1000 km²) from July 9 to September 12, 1977, in tussock tundra vegetation of Alaska's Seward Peninsula. The fire consumed most above ground vegetation. The frequency of northern Labrador tea in late May of the 1st postfire year was 0% on burned sites and 100% on unburned sites. By mid-June of the 1st postfire year, northern Labrador tea frequency on burned sites was 22% and 100% on unburned sites [89].

The recovery of northern Labrador tea on some burned tussock sites of Inuvik, Northwest Territories, took only 2 years. Researchers compared the annual production and nutrient content of northern Labrador tea on burned and unburned areas of 4 tussock communities. None of the fires were severe enough to kill entire tussocks, but did remove the evidence of shrubs and cryptogams. Site 1 burned in late June of 1969, and sites 2, 3, and 4 burned in August of 1968. The fire that burned site 4 was considered severe because of dry prefire conditions. The researchers noted that northern Labrador tea's recovery was the fastest of all shrub species investigated. The growth form of northern Labrador tea the 1st postfire year was abnormal; northern Labrador tea leaves were uncharacteristically thin and broad. This change in appearance was unnoticed by the 2nd postfire year. On sites 1 and 4, northern Labrador tea production was greater on burned than unburned sites by the 2nd postfire year. The production of northern Labrador tea on all sites is shown below [85]:

Site

1 2 3 4
Burn status B UB B UB B UB B UB
Postfire year 1 2 2 2
mean annual production
± (s x g/m²)
4.8±1 15±1.3 5.6±1.7 4.4±0.7 3.3±0.8 5.6±0.7 10.5±2.7 10.3±1.3

The nitrogen, phosphorus, potassium, and magnesium levels in northern Labrador tea plant tissues were significantly greater for burned plants. Below is the average nutrient content of northern Labrador tea plants from 4 burned sites and 1 unburned site [85].

Measurement % of dry weight ppm
Nutrient N** P** K* Ca Mg** Na Fe Mn
Burned 1.66 0.22 0.62 0.42 0.16 48.8 220 119
Unburned 1.21 0.16 0.46 0.5 0.14 44.8 199 1223
*Burned and unburned differences significant (p=0.05)
**Burned and unburned differences significant (p=0.01)

Early and later postfire effects: The following studies describe both early and later postfire recovery of northern Labrador tea. Northern Labrador tea is typically present in early postfire communities; fire severity influences recovery time and postfire coverage of northern Labrador tea. Portions of Alaska's Seward Peninsula burned in July of 1977 when temperatures averaged 5 degrees above normal, and precipitation levels were 5% of normal. Fires burned in 3 vegetation types, and severity varied. The vegetation burned is listed in order of increasing fire severity: tussock shrub tundra, wet sedge-shrub tundra, and dry shrub tundra. Northern Labrador tea coverage was reduced on all burned plots initially. However, decreased coverage was longer lived on those sites burned with greater severity. On tussock shrub tundra sites that burned least severely, northern Labrador tea density (shoots/m²) was significantly (p=0.1) greater the 2nd postfire year than the 1st postfire year on 4 out of 5 sites sampled. The increase averaged 49 shoots/m². The prefire and postfire northern Labrador tea coverages are summarized below [55,56,58].

Vegetation type Organic horizon removed Prefire Postfire year 1 Postfire year 2 Postfire year 3 Postfire year 24
Moist tussock-shrub tundra 5 cm 9% 1.2% 3.4% 4% 36%
Wet sedge-shrub tundra 5-15 cm 4% tr tr tr 1%
Dry shrub tundra ~50% 6% 0 0 0 1%

Fetcher and others [26] compared burned and unburned sites 1 and 13 years following a June 1969, fire that burned northwest of Fairbanks, Alaska, in sheathed cottonsedge communities. The fire did not burn severely enough to kill entire tussocks but removed all shrubs and cryptogams. Researchers found that the depth of thaw in the 13th postfire year was 20 inches (52 cm) on burned sites and 15 inches (39 cm) on unburned sites. These differences were significant (p<0.01). Northern Labrador tea production recovered by the 13th postfire year. The table below summarizes the findings of Fetcher and others [26].

Postfire year 1 13
Burn status B UB B UB
annual production ± s x (g/m²) 4.8±1 15±1.3 26.9±5.5 31.3±3.4

Northern Labrador tea recovered from a severe fire in tundra and forest-tundra vegetation of Inuvik, Northwest Territories, by the 22nd postfire year. The fire burned from August 8 through 18, 1968. Researchers described the deep-penetrating fire as burning with "unusually great severity." Fire scarred black spruce trees suggest the area last burned 120 years ago. Burned and unburned sites were compared in August of 1973, and burned sites were resampled in August of 1990. Northern Labrador tea was present immediately following fire. Northern Labrador tea coverage on burned sites was significantly (p<0.01) greater than in previously unburned tundra vegetation by 1990. Northern Labrador tea recovery is summarized below [43]:

Site

Forest-tundra ecotone (n=9)

Tundra (n=15)
Burn status unburned burned unburned burned
Postfire year 5 5 22 5 5 22
% cover ± s x 18.5±2.1 4.4±1.2* 16.3>±4.7 15.1±2.2 6.4±1.2 26.8±2.7*
* Burned and unburned differences are significant at p<0.01.

On peat and lichen plateaus of Chick Lake Basin, Northwest Territories, the coverage of northern Labrador tea on different aged burned sites was compared. Fire characteristics were not provided. The coverage of northern Labrador tea on peat plateaus burned 4 years earlier was 2%, on sites burned 53 years prior was 48%, and on sites burned 92 years ago was 24%. On lichen plateaus, coverage of northern Labrador tea was 28% on sites burned 44 years earlier, 32% on sites burned 47 years prior, and 6% on sites burned 100 years ago [64].

After visiting 130 white spruce- and black spruce-dominated stands that burned between 1 month and 200 years earlier in the taiga of interior Alaska, Foote [28] summarized the changes in northern Labrador tea coverage and frequency in black spruce stands. Fire severity was not reported. The results are presented below. It is likely that unknown differences in sampled communities could have been as important as time since fire in resulting northern Labrador tea coverage.

Mean time since fire
(number of stands sampled)
Frequency (%) Coverage (%)
5 weeks (n=3) 0 0
2 years (n=19) 16 8
10 years (n=21) 1 3
48 years (n=12) 18 1
70 years (n=11) 1 7
121 years (n=4) 16 2

Swanson [75] studied northern Labrador tea coverage and constancy on different permafrost soils as they related to time since fire. Sites were in boreal forests of the Kobak Preserve in northwestern Alaska. Included postfire communities were open black spruce, black spruce with paper birch and quaking aspen, and white spruce with mountain alder. Postfire soils were described as frozen, thawed, and dry. Frozen soils remained frozen even after fire. Thawed soils were wet soils with permafrost before the fire, but drier and lacking permafrost within the top 3 feet (1 m) after fire. Dry soils had no evidence of past wetness or permafrost in the top 3 feet (1 m) prior to burning. Time since fire was not as important as soil type in predicting northern Labrador tea coverage which was lowest on dry soils. Study results are summarized below:

Soil type Frozen Frozen Thawed Dry Dry
Time since fire (years) 10-50 >100 10-50 10-50 >100
Constancy (%) 100 100 100 95 100
Cover (%) 50 42 51 23 35

FIRE MANAGEMENT CONSIDERATIONS:
While northern Labrador tea coverage, frequency, and/or production is often decreased initially by fire, these changes are short lived, and northern Labrador tea does not require protection from periodic fire.

The following study investigated northern Labrador tea's fuel characteristics which may be valuable to its fire management. In the forest-tundra vegetation of Inuvik, Northwest Territories, researchers collected plant leaves and stems in July and late August of 1974 and 1975. In 1975, the study area experienced drought conditions. All northern Labrador tea fuel was less than 0.25 inch (6.4 mm) in diameter. Of the live vascular plants investigated in the study area, northern Labrador tea's fuel potential rating was highest. Below are the measured fuel characteristics [76]:

Fuel characteristic Mean height (cm) Surface/volume ratio (mmˉ¹) Moisture content (%) Caloric content (cal/g)
Leaves 18 3.2 91% 5550
Stems NA 2.1 78% 5320

MANAGEMENT CONSIDERATIONS

SPECIES: Ledum palustre
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Northern Labrador tea is often found in preferred ungulate grazing sites and important small mammal and bird habitats. However, northern Labrador tea is not considered palatable and likely is not an important food source. If browsed, northern Labrador tea would be most vulnerable to damage in the fall [12].

Caribou: Alaska and northern Canada's arctic and subarctic communities in which northern Labrador tea is common are important caribou habitat [32,47]. Rumen contents of 20 caribou collected in December and January from Manitoba, Saskatchewan, and the Northwest Territories contained 2.9% northern Labrador tea. The highest concentration (4.9%) was found in 4 rumen contents collected in the Northwest Territories [65]. However, in feeding sites of northwestern Manitoba and north-central Saskatchewan, northern Labrador tea was not purposefully consumed [51].

The following study of 500 to 1,000 caribou that became stranded on the 15 mi² (40 km²) Rideout Island of the Northwest Territories in the summer of 1987 suggests that northern Labrador tea may be consumed when other more palatable vegetation is unavailable. The stranded caribou died of malnutrition after severely grazing the island vegetation. The researcher visited the island in late July of the following year and compared it to similar mainland communities. No northern Labrador tea on the mainland was browsed, while browsing of northern Labrador tea on the island averaged 5%. Likely decreases in northern Labrador tea coverage on the island reflect both browsing and trampling damage [33].

Area Island Mainland
Cover (%) ± s x in low shrub tundra 2±1 7±2*
Cover (%) in tussock tundra 6±2 4±2
Mean % of browsed shoots (both communities) 5±3 (n=8) 0 (n=4)
*significant (p<0.05) 

Deer: The single study that addressed northern Labrador tea in black-tailed deer feeding suggests that northern Labrador tea is not utilized as a food source. Feces collected in the summer on Admiralty Island of southeastern Alaska contained a trace (<0.5%) amount of northern Labrador tea. The composition that was northern Labrador tea in feces collected in all other seasons was 0% [31].

Moose: LeResche and Davis [45] report that moose on the Kenai Peninsula of Alaska occasionally feed on northern Labrador tea throughout the year.

Small mammals: Tundra vegetation in which northern Labrador tea is typical is important habitat for many small mammals such as arctic foxes, arctic ground squirrels, brown lemmings, collared lemmings, and common muskrats. Wolverines utilize tundra vegetation in the winter. Shrub, sedge, and black spruce tundra vegetation is important to American minks, northern red-backed voles, and/or tundra voles [47,87].

Birds: Northern Labrador tea tundra habitat is important to many breeding and nesting birds. Common loons, yellow-billed loons, arctic loons, gyrfalcons, snowy owls, black-bellied plovers, semipalmated plovers, and dunlins use tundra vegetation as breeding habitat [47]. The tundra nesters include brants, white-fronted geese, northern shovelers, and whimbrels. Whistling swans nest in both moist sedge and low shrub tundra. Rock ptarmigans nest exclusively in tundra vegetation. Willow ptarmigans use dry shrub and tussock tundra habitats in the summer and nest in open forest tundra. Surf scoters aggregate in molting flocks on tundra sites [47]. The Lapland longspurs utilize tussock tundra habitats where northern Labrador tea is very common [89].

Palatability/nutritional value: Northern Labrador tea's leaves and twigs are very unpalatable and have low digestibility [9,33]. Phenolic resins, terpenes, saponins, and tannins are present in high concentrations in northern Labrador tea [11]. Northern Labrador tea is also thought to contain ledol, a poison that causes cramping or paralysis [37]. Several researchers suggest that northern Labrador tea's chemical defenses are an evolutionary adaptation that allows northern Labrador tea to retain nutrients stored in above ground plant parts [9,11].

Below are the total nitrogen and calcium contained in above and below ground northern Labrador tea structures collected from Alaskan tundra. Presented is the average milligram per individual. Sample size was 4 [12].

Nutrient

Nitrogen Calcium
Sampling date July 23 August 25 July 23 August 25
current leaves and stem 2.2 3.4 0.37 0.86
1-year leaves 1.7 1.7 0.74 0.75
1-year stem 0.4 0.4 0.2 0.15
2-year (and older) leaves 1.3 1.3 0.79 0.84
2-year (and older) stem 1.0 1.0 0.38 0.35
above-ground main stem 1.8 1.9 0.46 0.45
below-ground main stem 2.3 2.2 0.48 0.51
roots 2.1 2.1 0.5 0.46

The seasonal changes in the chemical composition (%) of northern Labrador tea leaves collected from Reindeer Preserve near Inuvik, Northwest Territories, are presented below. Scotter [66] notes that northern Labrador tea crude fat was significantly (p<0.05) higher than most of the other 8 species investigated.

Nutrient
(% composition)
Crude protein Crude fat Crude fiber N-free extract Ash Ca P Carotene
(mg/lb of forage)
July 9.6 10.3 29.8 47.3 3 0.5 0.1 13.4
August 7.6 10.5 23.8 54.7 3.4 0.6 0.1 7.5
November 7.8 9.1 23.6 56.5 3 0.6 0.1 11.4
February 8 10.1 26.2 52.7 3 0.6 0.1 13.1
May 7.8 10.5 26.9 51.3 3.5 0.6 0.1 12.8

For information regarding changes in the nutrient content of northern Labrador tea plant tissue following fire, see the fire effects section of this review.

Cover value: No information is available on this topic.

VALUE FOR REHABILITATION OF DISTURBED SITES:
No information is available on this topic.

OTHER USES:
Northern Labrador tea has several medicinal uses. A tea of northern Labrador leaves soothes stomach aches and sore throats. The tea may also provide strength to someone who has bled heavily. Northern Labrador tea leaves when chewed relieve toothaches and canker sores. When leaves are made into an ointment with seal fat, it can be used to treat eye disorders, moisten skin, and ease breathing when rubbed on the chest ([1] cited others). Native people of Fort Yukon, northeastern Alaska, suggest that northern Labrador tea leaves and stems boiled into a tea aid in the healing of colds and hangovers [36]. Research suggests that northern Labrador tea has anti-inflammatory properties useful in treating rheumatism, degenerative joint disease, and insect bites [20].

OTHER MANAGEMENT CONSIDERATIONS:
Many have investigated northern Labrador tea's growth as it relates to its habitat. In Canada, northern Labrador tea typically grows on nutrient-poor soils with dry soil moisture regimes. Northern Labrador tea is considered an indicator species for these site characteristics [63]. Other research includes experimental studies of climate change. Temperatures and carbon dioxide levels are often manipulated while northern Labrador tea and associated tundra species growth is monitored. The following references provide more information on how changes in climate may affect arctic species [13,35]. Further research into environmental conditions and northern Labrador tea growth was done by Yarie and Mead [90]. They provide the coefficients for predicting leaf, twig, and combined dry biomass in different communities that can be used in biomass estimation equations.


Ledum palustre: References


1. Aiken, S. G.; Dallwitz, M. J.; Consaul, L. L.; McJannet, C. L.; Gillespie, L. J.; Boles, R. L.; Argus, G. W.; Gillett, J. M.; Scott, P. J.; Elven, R.; LeBlanc, M. C.; Brysting, A. K.; Solstad, H. 1999. Ledum palustre subsp. decumbens (Aiton) Hulten, [Online]. In: Flora of the Canadian arctic archipelago. In: Descriptions, illustrations, interactive identification, and information retrieval from DELTA databases. Canadian Museum of Nature (Producer). Available: http://www.mun.ca/biology/delta/arcticf/_ca/www/erlepa.htm [2005, August 18]. [54283]

2. Anderson, J. P. 1959. Flora of Alaska and adjacent parts of Canada. Ames, IA: Iowa State University Press. 543 p. [9928]

3. Arno, Stephen F. 2000. Fire in western forest ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 97-120. [36984]

4. Bernard, Stephen R.; Brown, Kenneth F. 1977. Distribution of mammals, reptiles, and amphibians by BLM physiographic regions and A.W. Kuchler's associations for the eleven western states. Tech. Note 301. Denver, CO: U.S. Department of the Interior, Bureau of Land Management. 169 p. [434]

5. Bliss, L. C. 1988. Arctic tundra and polar desert biome. In: Barbour, Michael G.; Billings, William Dwight, eds. North American terrestrial vegetation. Cambridge; New York: Cambridge University Press: 1-32. [13877]

6. Bliss, L. C.; Wein, R. W. 1972. Plant community responses to disturbances in the western Canadian Arctic. Canadian Journal of Botany. 50: 1097-1109. [14877]

7. Boggs, Keith. 2000. Classification of community types, successional sequences, and landscapes of the Copper River Delta, Alaska. Gen. Tech. Rep. PNW-GTR-469. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 244 p. [38491]

8. Bret-Harte, M. Syndonia; Shaver, Gaius R.; Chapin, F. Stuart, III. 2002. Primary and secondary stem growth in arctic shrubs: implications for community response to environmental change. Journal of Ecology. 9(2): 251-267. [54275]

9. Bryant, John P.; Chapin, F. Stuart, III; Klein, David R. 1982. Carbon/nutrient balance of boreal plants in relation to vertebrate herbivory. Oikos. 40(3): 357-368. [54276]

10. Calmes, Mary A. 1976. Vegetation pattern of bottomland bogs in the Fairbanks area, Alaska. Fairbanks, AK: University of Alaska. 104 p. Thesis. [14785]

11. Chapin, F. S., III; McKendrick, J. D.; Johnson, D. A. 1986. Seasonal changes in carbon fractions in Alaskan tundra plants of differing growth form: implications for herbivory. Journal of Ecology. 74: 707-731. [21046]

12. Chapin, F. Stuart, III; Johnson, Douglas A.; McKendrick, Jay D. 1980. Seasonal movement of nutrients in plants of differing growth form in an Alaskan tundra ecosystem: implications for herbivory. Journal of Ecology. 68(1): 189-202. [54278]

13. Chapin, F. Stuart, III; Shaver, Gaius R. 1996. Physiological and growth responses of arctic plants to a field experiment simulating climate change. Ecology. 77(3): 822-840. [54277]

14. Chapin, F. Stuart, III; Van Cleve, Keith. 1981. Plant nutrient absorption and retention under differing fire regimes. In: Mooney, H. A.; Bonnicksen, T. M.; Christensen, N. L.; Lotan, J. E.; Reiners, W. A., technical coordinators. Fire regimes and ecosystem properties: Proceedings of the conference; 1978 December 11-15; Honolulu, HI. Gen. Tech. Rep. WO-26. Washington, DC: U.S. Department of Agriculture, Forest Service: 301-321. [4397]

15. Chester, Ann L.; Shaver, G. R. 1982. Reproductive effort in cotton grass tussock tundra. Holarctic Ecology. 5: 200-206. [21043]

16. Chester, Ann L.; Shaver, Gaius R. 1982. Seedling dynamics of some cotton grass tussock tundra species during the natural revegetation of small disturbed areas. Holarctic Ecology. 5: 207-211. [21048]

17. Cochrane, G. Ross; Rowe, J. S. 1969. Fire in the tundra at Rankin Inlet N.W.T. In: Proceedings, annual Tall Timbers fire ecology conference; 1969 April 10-11; Tallahassee, FL. No. 9. Tallahassee, FL: Tall Timbers Research Station: 61-74. [19348]

18. Densmore, Roseann V. 1997. Effect of day length on germination of seeds collected in Alaska. American Journal of Botany. 84(2): 274-278. [54720]

19. Drury, William H., Jr. 1956. Bog flats and physiographic processes in the Upper Kuskokwim River region, Alaska. Contributions from the Gray Herbarium No. 178. Cambridge, MA: Harvard University, The Gray Herbarium. 127 p. [12996]

20. Dubois, M.-A.; Wierer, M.; Wagner, H. 1990. Palustroside: a new coumarin glucoside ester from Ledum palustre. Planta Medica. 56(6): 664-665. [54279]

21. Duchesne, Luc C.; Hawkes, Brad C. 2000. Fire in northern ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 35-51. [36982]

22. Dyrness, C. T.; Grigal, D. F. 1979. Vegetation-soil relationships along a spruce forest transect in interior Alaska. Canadian Journal of Botany. 57: 2644-2656. [12488]

23. Ebersole, James J. 1987. Short-term vegetation recovery at an Alaskan arctic coastal plain site. Arctic and Alpine Research. 19(4): 442-450. [9476]

24. Ebersole, James J. 1989. Role of seed bank in providing colonizers on a tundra disturbance in Alaska. Canadian Journal of Botany. 67: 466-471. [21141]

25. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905]

26. Fetcher, Ned; Beatty, Thomas F.; Mullinax, Ben; Winkler, Daniel S. 1984. Changes in arctic tussock tundra thirteen years after fire. Ecology. 65(4): 1332-1333. [7234]

27. Flora of North America Association. 2004. Flora of North America: The flora. [Online]. Flora of North America Association (Producer). Available: http://www.fna.org/FNA. [36990]

28. Foote, M. Joan. 1983. Classification, description, and dynamics of plant communities after fire in the taiga of interior Alaska. Res. Pap. PNW-307. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 108 p. [7080]

29. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; Lewis, Mont E.; Smith, Dixie R. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998]

30. Gruell, G. E.; Loope, L. L. 1974. Relationships among aspen, fire, and ungulate browsing in Jackson Hole, Wyoming. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station. 33 p. In cooperation with: U.S. Department of the Interior, National Park Service, Rocky Mountain Region. [3862]

31. Hanley, Thomas A.; Robbins, Charles T.; Spalinger, Donald E. 1989. Forest habitats and the nutritional ecology of Sitka black-tailed deer: a research synthesis with implications for forest management. Gen. Tech. Rep. PNW-GTR-230. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 52 p. [7509]

32. Hanson, Herbert C. 1953. Vegetation types in northwestern Alaska and comparisons with communities in other arctic regions. Ecology. 34(1): 111-140. [9781]

33. Henry, G. H. R.; Gunn, A. 1991. Recovery of tundra vegetation after overgrazing by caribou in arctic Canada. Arctic. 44(1): 38-42. [14747]

34. Hernandez, Helios. 1973. Natural plant recolonization of surficial disturbances, Tuktoyaktuk Peninsula region, Northwest Territories. Canadian Journal of Botany. 51: 2177-2196. [20372]

35. Hobbie, Sarah E.; Shevtsova, Anna; Chapin, F. Stuart, III. 1999. Plant responses to species removal and experimental warming in Alaskan tussock tundra. Oikos. 84(3): 417-434. [54280]

36. Holloway, Patricia S.; Alexander, Ginny. 1990. Ethnobotany of the Fort Yukon region, Alaska. Economic Botany. 44(2): 214-225. [13625]

37. Hulten, Eric. 1968. Flora of Alaska and neighboring territories. Stanford, CA: Stanford University Press. 1008 p. [13403]

38. Karlin, E. F.; Bliss, L. C. 1983. Germination ecology of Ledum groenlandicum and Ledum palustre spp. decumbens. Arctic and Alpine Research. 15(3): 397-404. [51669]

39. Kartesz, John T.; Meacham, Christopher A. 1999. Synthesis of the North American flora (Windows Version 1.0), [CD-ROM]. Available: North Carolina Botanical Garden. In cooperation with the Nature Conservancy, Natural Resources Conservation Service, and U.S. Fish and Wildlife Service [2001, January 16]. [36715]

40. King, George A. 1993. Vegetation and pollen relationships in eastern Canada. Canadian Journal of Botany. 71: 193-210. [21449]

41. Kuchler, A. W. 1964. United States [Potential natural vegetation of the conterminous United States]. Special Publication No. 36. New York: American Geographical Society. 1:3,168,000; colored. [3455]

42. Kummerow, J. 1983. Root surface/leaf area ratios in arctic dwarf shrubs. Plant and Soil. 71(1-3): 395-399. [54281]

43. Landhausser, Simon M.; Wein, Ross W. 1993. Postfire vegetation recovery and tree establishment at the Arctic treeline: climate-change--vegetation response hypotheses. Journal of Ecology. 81: 665-672. [22741]

44. Larsen, James A. 1971. Vegetational relationships with air mass frequencies: boreal forest and tundra. Arctic. 24: 177-194. [8258]

45. LeResche, Robert E.; Davis, James L. 1973. Importance of nonbrowse foods to moose on the Kenai Peninsula, Alaska. Journal of Wildlife Management. 37(3): 279-287. [13123]

46. Mann, Daniel H.; Plug, Lawrence J. 1999. Vegetation and soil development at an upland taiga site, Alaska. Ecoscience. 6(2): 272-285. [36398]

47. Martell, Arthur M.; Dickinson, Dawn M.; Casselman, Lisa M. 1984. Wildlife of the Mackenzie Delta region. Occasional Publ. No. 15. Edmonton, AB: The University of Alberta, Boreal Institute for Northern Studies. 214 p. [15014]

48. McGraw, J. B. 1980. Seed bank size and distribution of seeds in cottongrass tussock tundra, Eagle Creek, Alaska. Canadian Journal of Botany. 58(15): 1607-1611. [51703]

49. McGraw, J. B.; Shaver, G. R. 1982. Seedling density and seedling survival in Alaskan cotton grass tussock tundra. Holarctic Ecology. 5: 212-217. [21041]

50. Meinecke, E. P. 1929. Quaking aspen: A study in applied forest pathology. Tech. Bull. No. 155. Washington, DC: U.S. Department of Agriculture. 34 p. [26669]

51. Miller, Donald Ray. 1976. Wildfire and caribou on the taiga ecosystem of northcentral Canada. Moscow, ID: University of Idaho. 129 p. Dissertation. [40270]

52. Murray, Carole; Miller, Philip C. 1982. Phenological observations of major plant growth forms and species in montane and Eriophorum vaginatum tussock tundra in central Alaska. Holarctic Ecology. 5: 109-116. [21044]

53. Oechel, Walter C. 1998. Nutrient and water flux in a small arctic watershed: an overview. Holarctic Ecology. 12(3): 229-237. [54282]

54. Pearce, C. M.; McLennan, D.; Cordes, L. D. 1988. The evolution and maintenance of white spruce woodlands on the Mackenzie Delta, N. W. T., Canada. Holarctic Ecology. 11(4): 248-258. [10472]

55. Racine, Charles H. 1979. The 1977 tundra fires in the Seward Peninsula, Alaska: effects and initial revegetation. BLM-Alaska Technical Report 4. Anchorage, AK: U.S. Department of the Interior, Bureau of Land Management, Alaska State Office. 51 p. [8330]

56. Racine, Charles H. 1981. Tundra fire effects on soils and three plant communities along a hill-slope gradient in the Seward Peninsula, Alaska. Arctic. 34(1): 71-84. [7233]

57. Racine, Charles H.; Johnson, Lawrence A.; Viereck, Leslie A. 1987. Patterns of vegetation recovery after tundra fires in northwestern Alaska, U.S.A. Arctic and Alpine Research. 19(4): 461-469. [6114]

58. Racine, Charles; Jandt, Randi; Meyers, Cynthia; Dennis, John. 2004. Tundra fire and vegetation change along a hillslope on the Seward Peninsula, Alaska, U.S.A. Arctic, Antarctic, and Alpine Research. 36(1): 1-10. [51694]

59. Raunkiaer, C. 1934. The life forms of plants and statistical plant geography. Oxford: Clarendon Press. 632 p. [2843]

60. Rees, Daniel C.; Juday, Glenn Patrick. 2002. Plant species diversity on logged versus burned sites in central Alaska. Forest Ecology and Management. 155: 291-302. [40745]

61. Reynolds, Keith M. 1990. Preliminary classification of forest vegetation of the Kenai Peninsula, Alaska. Res. Pap. PNW-RP-424. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 67 p. [14581]

62. Riley, J. L. 1979. Some new and interesting vascular plant records from northern Ontario. Canadian Field-Naturalist. 93(4): 355-362. [13845]

63. Ringius, Gordon S.; Sims, Richard A. 1997. Indicator plant species in Canadian forests. Ottawa, ON: Natural Resources Canada, Canadian Forest Service. 218 p. [35563]

64. Rowe, J. S.; Bergsteinsson, J. L.; Padbury, G. A.; Hermesh, R. 1974. Fire studies in the Mackenzie Valley. ALUR 73-74-61. Ottawa: Canadian Department of Indian and Northern Development. 123 p. [50174]

65. Scotter, George W. 1967. The winter diet of barren-ground caribou in northern Canada. Canadian Field-Naturalist. 81: 33-39. [16672]

66. Scotter, George W. 1972. Chemical composition of forage plants from the Reindeer Preserve, Northwest Territories. Arctic. 25(1): 21-27. [16563]

67. Scotter, George W. 1972. Fire as an ecological factor in boreal forest ecosystems of Canada. In: Fire in the environment: Symposium proceedings; 1972 May 1-5; Denver, CO. FS-276. [Washington, DC]: U.S. Department of Agriculture, Forest Service: 15-25. [13404]

68. Shaver, Gaius R. 1986. Woody stem production in Alaskan tundra shrubs. Ecology. 67(3): 660-669. [4928]

69. Shiflet, Thomas N., ed. 1994. Rangeland cover types of the United States. Denver, CO: Society for Range Management. 152 p. [23362]

70. Sirois, Luc; Payette, Serge. 1989. Postfire black spruce establishment in subarctic and boreal Quebec. Canadian Journal of Forestry Research. 19: 1571-1580. [10110]

71. Soper, James H.; Heimburger, Margaret L. 1982. Shrubs of Ontario. Life Sciences Miscellaneous Publications. Toronto, ON: Royal Ontario Museum. 495 p. [12907]

72. Stanek, W.; Alexander, K.; Simmons, C. S. 1981. Reconnaissance of vegetation and soils along the Dempster Highway, Yukon Territory: I. Vegetation types. BC-X-217. Victoria, BC: Environment Canada, Canadian Forestry Service, Pacific Forest Research Centre. 32 p. [16526]

73. Starr, Gregory; Oberbauer, Steven F. 2003. Photosynthesis of arctic evergreens under snow: implications for tundra ecosystem carbon balance. Ecology. 84(6): 1415-1420. [45200]

74. Stickney, Peter F. 1989. FEIS postfire regeneration workshop--April 12: Seral origin of species comprising secondary plant succession in Northern Rocky Mountain forests. 10 p. Unpublished draft on file at: U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Fire Sciences Laboratory, Missoula, MT. [20090]

75. Swanson, David K. 1996. Susceptibility of permafrost soils to deep thaw after forest fires in interior Alaska, U.S.A., and some ecologic implications. Arctic and Alpine Research. 28(2): 217-227. [26903]

76. Sylvester, T. W.; Wein, Ross W. 1981. Fuel characteristics of arctic plant species and simulated plant community flammability by Rothermel's model. Canadian Journal of Botany. 59: 898-907. [17685]

77. Timoney, Kevin P.; La Roi, George H.; Zoltai, Stephen C.; Robinson, Anne L. 1993. Vegetation communities and plant distributions and their relationships with parent materials in the forest-tundra of northwestern Canada. Ecography. 16: 174-188. [23007]

78. U.S. Department of Agriculture, Natural Resources Conservation Service. 2005. PLANTS database (2005), [Online]. Available: http://plants.usda.gov/. [34262]

79. Viereck, L. A.; Dyrness, C. T. 1979. Ecological effects of the Wickersham Dome Fire near Fairbanks, Alaska. Gen. Tech. Rep. PNW-90. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment Station. 71 p. [6392]

80. Viereck, Leslie A. 1970. Forest succession and soil development adjacent to the Chena River in interior Alaska. Arctic and Alpine Research. 2(1): 1-26. [12466]

81. Viereck, Leslie A.; Little, Elbert L., Jr. 1972. Alaska trees and shrubs. Agric. Handb. 410. Washington, DC: U.S. Department of Agriculture, Forest Service. 265 p. [6884]

82. Wade, Dale D.; Brock, Brent L.; Brose, Patrick H.; [and others]. 2000. Fire in eastern ecosystems. In: Brown, James K.; Smith, Jane Kapler, eds. Wildland fire in ecosystems: Effects of fire on flora. Gen. Tech. Rep. RMRS-GTR-42-vol. 2. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station: 53-96. [36983]

83. Wein, R. W. 1974. Recovery of vegetation in arctic regions after burning. Rep. 74-6. Ottawa, ON: Canadian Task Force on Northern Oil Development. 41 p. [13001]

84. Wein, R. W. 1975. Vegetation recovery in arctic tundra and forest-tundra after fire. ALUR Rep. 74-75-62. Ottawa, ON: Department of Indian Affairs and Northern Development, Arctic Land Use Research Program. 62 p. [12990]

85. Wein, Ross W.; Bliss, L. C. 1973. Changes in Arctic Eriophorum tussock communities following fire. Ecology. 54(4): 845-852. [9827]

86. Wein, Ross W.; Bliss, L. C. 1974. Primary production in arctic cottongrass tussock tundra communities. Arctic and Alpine Research. 6(3): 261-274. [21035]

87. West, Stephen D. 1982. Dynamics of colonization and abundance in central Alaskan populations of the northern red-backed vole, Clethrionomys rutilus. Journal of Mammalogy. 63(1): 128-143. [7300]

88. Wolff, Jerry O. 1980. The role of habitat patchiness in the population dynamics of snowshoe hares. Ecological Monographs. 50(1): 111-130. [25078]

89. Wright, John M. 1981. Response of nesting lapland longspurs (Calcarius lapponicus) to burned tundra on the Seward Peninsula. Arctic. 34(4): 366-369. [7885]

90. Yarie, John; Mead, Bert R. 1988. Twig and foliar biomass estimation equations for major plant species in the Tanana River basin of interior Alaska. Res. Pap. PNW-RP-401. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 20 p. [13487]

91. Youngblood, Andrew. 1993. Community type classification of forest vegetation in young, mixed stands, interior Alaska. Res. Pap. PNW-RP-458. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 42 p. [22029]




FEIS Home Page