Trading forage quality for quantity? Plant phenology and patch choice by Svalbard reindeer

Plant phenology of Luzula heathland plots in Spitsbergen (78 degrees N) was manipulated by adding or removing snow, which altered the time for plots ( 2 mx2 m; n=10) to become snow-fret. A 2-week difference in snowmelt, equiva lent to approximately one-sixth of the growing season, was achieved between advanced (first to be snow-free) and delayed (last to be snow-free) treatm ents, which influenced plant biomass and plant quality. Nitrogen content of the forage species decreased with time after snowmelt, whereas C:N ratio i ncreased. Manipulation of snowmelt led to a shift in "phenological time", w ithout altering these plant quality parameters as such. Early in the growin g season, Svalbard reindeer (Rangifer tarandus platyrhynchus) selected the advanced plots which had been snow-free for longest, presumably because of the greater biomass of both Luzula confusa and Salix polaris, major compone nts of reindeer diet at that time of the year. Moreover, the proportion of live Luzula leaves was highest in advanced plots, relative to both unmanipu lated control and delayed plots. In contrast, plant quality, measured as ni trogen content and C:N ratio of leaves, was lowest in the preferred plots. Phenolic content did not differ among treatments, and is therefore unlikely to play a role in reindeer selection for plots with early snowmelt. Unlike in temperate regions, where selection for plant quality seems to be of maj or importance, selection for plant quantity might be an outcome of generall y low levels of plant biomass and high forage quality during the growing se ason in the high Arctic. Reindeer selection for high plant biomass is likel y to lead to a more favourable nitrogen and energy return than selection fo r high plant quality.