Autumn Foraging Dynamics of Woodland Caribou in Experimentally Manipulated Habitats, Northeastern Washington, USA

Abstract

Foraging options of woodland caribou (Rangifer tarandus caribou) in the high snowpack ecosystems of western North America become narrowed after freezing temperatures in antumn precipitate leaf-drop in deciduous shrubs. The objectives of this research were to determine the influence of (1) removing arborca lichen (Ascompecytes) on windthrown trees and myrtle boxwood (Pachistime myrsinites) and (2) stand type (oldgrowth versus clearcnt) on woodland caribou foraging dynamics during autum. Foraging trials were conducted with 3 tame woodland caribou in 6 0.5-ha pens. In 3 treatment pens all windthrown arboreal lichen-bearing trees were removed from the old-growth portion of the pen and extant invrtle hoxwood plants were removed from the entire pen. In the 3 control pens all extant windthrown trees and invrtle boxwood plants were retained In addition, pens were constructed such that half of each pen was in an old-growth stand of western red-cedar (Thuja plicata)-western hemlock (Tsuga heterophylla) and half was in an adjacent clearent. Arboreal hcher had the greatest influence on dry-matter intake rate (DMIR) because of the large bite size provided by this forage. In control pens, caribou had higher DMIR (P = 0.006) and crude protein intake rate (CPIR) (P = 0.007) than in treatment pens where lichen-bearing windthrown trees had been removed. Arboreal lichen from windthrown trees was 52% (range 43-61) of the total DMI in the old-growth portious of control pens Arboreal lichen from windthrown trees comprised 81% (range = 75-92) of the arboreal lichen bites (i.e., 19% of arboreal lichen bites were from litterfall and standing trees), and 28% range = 16-48) of total bites in the timbered portion of control peus. The DMIR (P = 0.004) and CPIR (P = 0.004) of caribou was also greater in old-growth than in clearcat portions of pens. Search time was greater (P = 0.008) in clearent portions or pens than in old-growth portions. Myrtle boxwood comprised <0.4% of caribou diets. These data suggest that arboreal lichen is an important dietary component earlier in antamn than previously reported.