Arctic Institute: Forest structure hare impacts
Charles Krebs describes snowshoe hare population cycles in a 2011 article. In the article he said, "Snowshoe hares across the boreal forest are a key food for many predators and their cycles have been the subject of large-scale field experiments that have pinpointed predation as the key limiting factor causing these fluctuations. Predators kill hares directly and indirectly stress them by unsuccessful pursuits. Stress reduces the reproductive rate of female hares and is transmitted to their offspring who also suffer reduced reproductive rates. The maternal effects produced by predation risk induce a time lag in the response of hare reproductive rate to density, aiding the cyclic dynamics. ... In the boreal forest of the southwestern Yukon, for example, moose and bears represent only 13.6 per cent of the vertebrate biomass and only 2.6 per cent of the energy flow ([1], p. 6). By contrast, snowshoe hares (Lepus americanus) represent 48 per cent of the biomass and 41 per cent of the average energy flow in this ecosystem.... We began in 1986 a second set of experiments manipulating both food and predation, and found that most hares (greater than 90%) died from predation and virtually none from starvation [20,45]. Predation mortality was clearly the dominant process driving hare numbers in the Kluane region. But the problem was that our large-scale experiments identified a joint food supply–predation manipulation as the major effect on hare numbers [46]. How was this possible when our studies showed no signs of food shortage even at the peak of the hare cycle and food-addition experiments failed to affect the rate of population collapse .... Snowshoe hares have a strong impact on shrub growth in the Kluane region, so that while winter food supplies do not limit hare density, hares reduce shrub biomass [51]. This effect has resulted in a spurt of growth in dwarf birch (B. glandulosa) in the Kluane region after the weak hare peak of 2006. Figure 6 shows the declining rate of browsing on willow and birch over three cycles. Dwarf birch is the snowshoe hare's favourite winter food in this area [51]. During the relatively low peak of 2006, few twigs of dwarf birch were completely browsed but many were partly browsed.
ES classes became involved following a visit to the Kluane Research Station in 1997. At that time we set out three forest structure plots and expanded the sampling to include a catalogue of browsed shrubs. Classes conducted these studies over a period of four years.
Charles Krebs describes snowshoe hare population cycles in a 2011 article. In the article he said, "Snowshoe hares across the boreal forest are a key food for many predators and their cycles have been the subject of large-scale field experiments that have pinpointed predation as the key limiting factor causing these fluctuations. Predators kill hares directly and indirectly stress them by unsuccessful pursuits. Stress reduces the reproductive rate of female hares and is transmitted to their offspring who also suffer reduced reproductive rates. The maternal effects produced by predation risk induce a time lag in the response of hare reproductive rate to density, aiding the cyclic dynamics. ... In the boreal forest of the southwestern Yukon, for example, moose and bears represent only 13.6 per cent of the vertebrate biomass and only 2.6 per cent of the energy flow ([1], p. 6). By contrast, snowshoe hares (Lepus americanus) represent 48 per cent of the biomass and 41 per cent of the average energy flow in this ecosystem.... We began in 1986 a second set of experiments manipulating both food and predation, and found that most hares (greater than 90%) died from predation and virtually none from starvation [20,45]. Predation mortality was clearly the dominant process driving hare numbers in the Kluane region. But the problem was that our large-scale experiments identified a joint food supply–predation manipulation as the major effect on hare numbers [46]. How was this possible when our studies showed no signs of food shortage even at the peak of the hare cycle and food-addition experiments failed to affect the rate of population collapse .... Snowshoe hares have a strong impact on shrub growth in the Kluane region, so that while winter food supplies do not limit hare density, hares reduce shrub biomass [51]. This effect has resulted in a spurt of growth in dwarf birch (B. glandulosa) in the Kluane region after the weak hare peak of 2006. Figure 6 shows the declining rate of browsing on willow and birch over three cycles. Dwarf birch is the snowshoe hare's favourite winter food in this area [51]. During the relatively low peak of 2006, few twigs of dwarf birch were completely browsed but many were partly browsed.
ES classes became involved following a visit to the Kluane Research Station in 1997. At that time we set out three forest structure plots and expanded the sampling to include a catalogue of browsed shrubs. Classes conducted these studies over a period of four years.