Interior Alaska is one of the last, great intact ecosystems in the world, with a rich abundance of wildlife species, many of which are scarce in the Lower 48. Many of these species are of profound economic and cultural importance for rural and urban residents of Interior Alaska.
Credit: Marie Thoms
Studies of mammalian herbivory, particularly by of moose and snowshoe hares, have been part of the Bonanza Creek LTER project for more than 20 years. Winter browsing by moose results in the consumption of up to 50% of the annual twig production of preferred forage such as willows, and a delay in green-up in the spring by approximately 8-10 days. Moose browsing opens up the canopy resulting in warmer and drier soils, which in turn have significant effects on other soils. Moose prefer to browse on willows instead of alder, and as a consequence contribute to a shift of dominance of willows to dominance of nitrogen-fixing alder. Thus, herbivory appears to accelerate successional change.
Credit: Knut Kielland
Whereas moose concentrate on deciduous species in early succession, seedlings of all tree species in Alaska's boreal forest may be subject to herbivory. For example, regenerating spruce seedlings are typically browsed heavily by snowshoe hares. This browsing typically result in curtailed height growth as well as high rates of mortality. When hares are abundant they impart high rate of mortality on spruce seedlings, suggesting that if masting in white spruce (which typically occurs every 10 years) coincides with the peak of the hares cycle (which also has a period of about 10 years) a large proportion of the current spruce cohort may die, consequently resulting in a delay of the establishment and dominance of spruce in succession.
Credit: Knut Kielland
Since 2008 we have been monitoring seasonal patterns of hare mortality and causes using radio telemetry. Survival of hares may be nearly 100% during the summer, but declines sharply during late fall when hares molt, food sources change, and the population, mostly composed of young-of-the-year individuals, face a new world with the onset of winter. Sources of mortality appear to be related to the density of vegetation. Thus, hares in spruce stands are mostly killed by lynx, whereas hares in riparian stands, which has less cover, are more often killed by avian predators such as goshawks.