The influence of variable snowpacks on habitat use by mountain caribou

Rangifer 01/2010;
Source: DOAJ

ABSTRACT Mountain caribou (Rangifer tarandus caribou) in southeastern British Columbia subsist for most of the winter on arboreal hair lichen, mostly Bryoria spp. Foraging occurs mainly in old subalpine fir (Abies lasiocarpa) forests near treeline. Here, the lower limit of Bryoria in the canopy is dictated by snowpack depth because hair lichens die when buried in snow. Bryoria is often beyond the reach of caribou in early winter, prompting caribou to move downslope to where lichen occurs lower in the canopy and other foraging modes are possible. Snowpacks are normally deep enough by late winter that caribou can reach Bryoria where it is most abundant, at high elevations. Extending this to inter-annual comparisons, Bryoria should be less accessible during late winter of low-snow years following normal winters, or of normal to low-snow years after deep-snow winters. We hypothesized that when maximum snowpack in late winter is low relative to the deepest of the previous 5 years, mountain caribou will use lower elevations to facilitate foraging (“lichen-snow-caribou” or LSC hypothesis). We tested this with late-winter data from 13 subpopulations. In the dry climatic region generally and for minor snowfall differences in wet and very wet regions, caribou did not shift downslope or in fact were at higher elevations during relatively low-snow years, possibly reflecting the ease of locomotion. The LSC hypothesis was supported within wet and very wet regions when snowpacks were about 1 m or more lower than in recent years. Elevation declined by 300 m (median) to 600 m (25th percentile) for snowpack differences of at least 1.5 m. Greater use of lodgepole pine and western hemlock stands sometimes also occurred. Management strategies emphasizing subalpine fir stands near treeline should be re-examined to ensure protection of a broader range of winter habitats used by caribou under variable snowpack conditions.

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    ABSTRACT: Caribou (Rangifer tarandus) in British Columbia are classified into mountain, northern and boreal ecotypes based on behavioural and ecological characteristics. We recognized 12 mountain caribou herds, 27 northern caribou herds, and an area occupied by low density boreal caribou dispersed in the boreal forests of the northeast portion of the province. Abundance estimates were usually based on attempts at total counts made from the air. Trends were based on repeated population estimates or the difference between recruitment and mortality rates for each herd. In 1996 the-re were approximately 18 000 caribou in British Columbia; 2300 mountain and 15 600 northern and boreal. These estimates suggest a slight increase in the numbers of both ecotypes over the last 18 years. Fifteen percent of the herds were reportedly increasing, 10% were decreasing, 31% were stable, but for 44% of the herds the trend was unknown. Historically caribou were found throughout 8 of the 14 biogeoclimatic zones in B.C. Caribou are now rarely found in the Sub-Boreal Spruce zone, likely due ro increased predation from wolves that increased in response to increasing moo-se numbers. Ranges of several herds in the Engelmann Spruce — Subalpine Fir and Alpine Tundra zones of south-eas-tern British Columbia are also reduced relative to historic conditions, probably because of habitat loss, habitat fragmen-tation, predation and hunting. Forest harvesting represents the greatest threat to caribou habitat and current research focuses on the mitigation of forest harvesting impacts.
    Rangifer. 03/1998; 18(5).
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    ABSTRACT: The mountain caribou is a threatened ecotype of the woodland caribou restricted to east-central and southeast British Columbia as well as adjacent portions of Washington and Idaho. In winter these animals forage almost exclusively on arboreal hair lichens, especially Bryoria. Here we examine the vertical and horizontal occurrence of hair lichens within the canopy of a mid-successional, mid-elevational forest dominated by Engelmann spruce and subalpine fir. Our study yielded five key findings: 1) all hair lichen species potentially important to caribou are present 60 yr after stand initiation; 2) low-biomass sorediate species (mostly B. fuscescens) predominate in the lower and middle canopies; 3) high-biomass non-sorediate species (mostly B. fremontii and B. pseudofuscescens) are most abundant in the upper canopy; 4) hair lichen biomass is higher in open stands than in closed stands; and 5) hair lichen loadings are low when compared with earlier reports from old-growth stands. The last finding apparently reflects—in the upper canopy—a lack of defoliated branches and—in the middle and lower canopies—humid, poorly ventilated conditions. We suggest that a judicial use of stand thinning could considerably augment the production of non-sorediate Bryoria species in defoliated portions of the middle canopy. Within the lower canopy, however, thinning is unlikely to increase Bryoria loadings, except as a result of inoculation from the middle canopy.
    The Bryologist 01/2009; · 0.98 Impact Factor

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