Interaction of Snowshoe Hares and Woody Vegetation

Aspen: Ecology and management in the western United States

“…During population peaks in Alberta, Pease et al (1979) found that browsing by hares was so great that food supplies became limiting. About 50% of the woody stems were severely browsed during the peak; but only 2% were being browsed 2 years later, after the population declined drastically.…”

“…This may not be so in Canada and Alaska, where snowshoe hare abundance at cyclic peaks may exceed the winter food supply. More than 50•‹/o of available browse (less than 0.5 inch (1.5 cm) diameter) was removed in winter by hares during population highs in Alberta (Pease et al 1979). …”

Role of Food in Hare Population Cycles

“…In November 1970, at the outset of a winter of peak hare densities, we began to measure food supplies on study areas in central Alberta. Food was insufficient to support hare populations in this peak winter and the winter following, and there was probably also food shortage during the third winter (Pease et al 1979). This was the first quantification of food shortage during a cyclic peak and decline.…”

Animal’s Functional Role in the Landscape

“…In general, snowshoe hares killed by lynx are in a bad physical condition (Pease et al 1979 ;Keith 1983 ;Keith et al 1984 ;Smith et al 1988 ). Thus, snowshoe hare decline is very likely due to shortage of food, in particular of high-quality food.…”

“…Likewise, chemical defensive substances formed in response to overgrazing by lemmings, microtines and snow hare make the food inedible for these herbivores and contribute to the decline of herbivore density during the population cycles (Haukioja and Hakala 1975 ;Pease et al 1979 ;Haukioja 1980 ;Laine and Henttonen 1983 ). In areas with pronounced 10-year snow hare cycles ( Lepus timidus and Lepus americanus , Alaska, Siberia ;Wolf 1980 ;Keith 1983 ), birches and willows produce more defenses than in Finland, for example, where such cycles do not occur (Keith 1983 ;Bryant et al 1989 ).…”