Snowshoe hares (Lepus americanus) are keystone herbivores in boreal forest, an important phenomenon because of their dramatic ten-year population cycles. Their population dynamics in their southern range are as yet poorly understood, but have been postulated to be less cyclic owing in part to habitat heterogeneity. In southern parts of their range, there has also been substantial interest in how forest stand structure (especially in response to forestry activities) affects hare dynamics, primarily because snowshoe hares are essential prey for the federally Threatened Canada lynx (Lynx canadensis). Although numerous studies have examined habitat use by hares, few have examined how habitat structure affects multi-year variability in hare density. We examine how snowshoe hare density varies in several common forest stand types in northwestern Montana and Yellowstone National Park, Wyoming.
Results/Conclusions Snowshoe hare densities in Montana, estimated via mark-recapture live-trapping on thirteen forest stands from 2001-2007, ranged from 0 to 3.1 hares per hectare. Densities per stand varied through time 2.1 to 38.9-fold. The three stand types, precommercially thinned, unthinned regeneration post-harvest, and mature unharvested, did not differ in these metrics. Understory structure from 0.5-1.0 and 1.0-1.5 m above the forest floor correlated with amplitude, but other structural attributes of the forest stands were not correlated either with mean density or variability. Two sites that were experimentally precommercially thinned with retention patches showed substantial declines in hare density. In Yellowstone, over 36% of surveyed stands did not support any hares. Mature forest cover types were more likely to have hares than were stands regenerating after the 1988 fires, but very few stands supported high numbers; 96% of stands had <0.5 hares/ha. Three stands that burned in 2003 had hares before the fire, but none afterward. Hare numbers fluctuated modestly over time, but patterns in Yellowstone were not indicative of a cycle.
We conclude that a) some southern populations of snowshoe hares have high inter-annual variability that is potentially cyclic, b) precommercial thinning and fire are detrimental to hares in the first few years, but as stands regain structural complexity higher hare densities can be supported, c) mature, thinned, and regenerating stands can all support high hare densities, but there are clear regional differences in the numbers of hares supported, d) stand structure is potentially related to temporal variability in snowshoe hare densities.
