Characteristics of Early-Winter Caribou, <em>Rangifer tarandus caribou</em>, Feeding Sites in the Southern Purcell Mountains, British Columbia

Abstract

Mountain Caribou are a rare ecotype of Woodland Caribou (Rangifer tarandus caribou) inhabiting the high-snowfall region of southeastern British Columbia, and are defined by their late-winter reliance on arboreal hair lichen of the genus Bryoria. During early winter, there is considerable variation in habitat use among populations. We snow-trailed Caribou in the southern Purcell Mountains during early winter to determine foraging patterns for the Purcell population. When snow was ≤51 cm deep, Caribou fed on Grouseberry (Vaccinium scoparium), the terrestrial lichen Cladonia, and arboreal lichens of the genus Bryoria. When snow was ≥62 cm deep, they ate exclusively arboreal lichens. In both periods, Caribou ate arboreal lichen from essentially every downed tree or branch encountered and fed with a higher intensity at downed trees than standing trees. During the low-snow period, Caribou fed at fewer trees but used those with greater lichen abundance, and fed more intensively at each, compared to the deep-snow period. In comparison to trees occurring on the foraging path but at which Caribou did not feed, those from which arboreal lichen was foraged intensively were of larger diameter, had greater lichen abundance, and were more likely to be Subalpine Fir (Abies lasiocarpa) or Engelmann Spruce (Picea engelmannii) and less likely to be Whitebark Pine (Pinus albicaulis), Lodgepole Pine (P. contorta) or Alpine Larch (Larix lyalli). The shift in diet between the low-snow and deep-snow periods reflected two modes of foraging within the early winter period, distinct from one another and apparently also distinct from the late-winter season. Management for early-winter habitat will require retention of some commercially significant forest across extensive areas, both near the subalpine forest – subalpine parkland ecotone and lower in the subalpine forest.

A synthesis of scale-dependent ecology of the endangered mountain caribou in British Columbia, Canada

“…For example, Rominger & Oldemeyer (1989), Terry et al (2000), Kinley et al (2003) and Serrouya et al (2007) found that old stands used by caribou contained five times more windthrow compared to old stands on average. These fallen trees provide an abundant source of easily accessible lichen to caribou, and the upper canopy often contains more Bryoria spp., which is the genus generally preferred by caribou.…”

“…These fallen trees provide an abundant source of easily accessible lichen to caribou, and the upper canopy often contains more Bryoria spp., which is the genus generally preferred by caribou. Caribou feed intensively on the lichen from windthrown trees and litterfall (Terry et al, 2000;Kinley et al, 2003;Serrouya et al, 2007). Another important source of variation was the size of trees.…”

“…In low-elevation cedar-hemlock forests, Serrouya et al (2007) report that caribou foraging paths contained 43% more trees >30 cm in diameter relative to random stands. Kinley et al (2003) reported that caribou in higher elevation spruce/fir (Picea engelmannii / Abies lasiocarpa) forests also foraged in areas with larger trees.…”

“…Large amount of lichens are mainly available to caribou through litterfall from the canopy and recently windthrown trees. In the lowest snowfall regions with mountain caribou, they appear to feed more on lichen from standing trees early in winter (Kinley et al, 2003) because lichens are more abundant low…”

“…Because snow is substantially deeper in areas occupied by mountain caribou than elsewhere within woodland caribou range, winter foraging opportunities are more limited. These caribou forage mainly on arboreal lichen, but because trees with sufficient lichen accumulation are older than will be grown during a typical forestry rotation, a conflict exists between forests managed primarily for fibre extraction and for caribou winter foraging habitat (Rominger & Oldemeyer, 1989;Kinley et al, 2003;Serrouya et al, 2007).…”