Seasonal and annual variability in the quality of important forage plants on Banks Island, Canadian High Arctic

In vitro acid-pepsin digestibility (IVDMD), crude protein (CP), fibre, lignin, and energy content were measured for a variety of forage plants collected annually from Banks Island over five summers and three winters from 1993-1998. Summer samples were collected during mid-June (start of growing season), mid-July (peak of growing season), and mid-late August (senescence). Winter samples were collected in early (November), mid- (February), and late- (April/May) winter, Samples, collected in areas of both high and low muskox density, included Carex aquatilis, unidentified Carex, Salix arctica, Dryas integrifolia, Cassiope tetragona, Saxifraga spp., Astragalus spp., Oxytropis spp., lichen, and grass. Seasonal dynamics in forage quality during the growing season were similar to those reported elsewhere in the arctic and high arctic and were consistent across years. However, there were significant year effects in lignin, Fibre, and energy content of forages and the crude protein (CP) content of C aquatilis in winter, indicating annual differences in the quality of forage available to herbivores. The quality of forages on Banks Island was similar between areas subjected to different densities of muskox (ca. 1.6-1.9 versus 0.3-0.4/km(2)) implying that quality was not affected by these gazing intensities. The Banks Island high arctic ecosystem supports an abundance of herbivores. It has been hypothesized that this is because forage quality and/or quantity are superior on Banks Island than elsewhere in the high arctic. Our results regarding forage quality are equivocal. Although the maximum CP content of forages from Banks Island was generally higher than reported elsewhere in the arctic and high arctic, CP content reported elsewhere fell within the interannual range reported from Banks Island. Fibre and energy content of forages from Banks Island were similar to slightly lower than elsewhere in the arctic and high arctic. Such comparisons must be considered in light of the interannual variability in quality we report.