Do high-density patches of coarse wood and regenerating saplings create browsing refugia for aspen (Populus tremuloides Michx.) in Yellowstone National Park (USA)?

Following the extensive 1988 fires in Yellowstone, a mosaic of high-density patches of fallen logs and regenerating lodgepole pine (Pinus contorta var. latifolia Engelm. ex Wats.) saplings developed in the landscape. Such patches could potentially provide browsing refugia for post-fire aspen (Populus tremuloides Michx.) seedlings. We asked two primary research questions: (1) Do elk (Cervus elaphus L.) reduce their use of high-density patches of coarse-wood and pine saplings? and (2) Are the abundance, height, and probability of presence of aspen positively related to the density of coarse wood or pine saplings? We visited 65 sites distributed across density gradients of downed wood and regenerating saplings. At each site, aspen seedlings were counted along five 50 m × 2 m belt transects. The height, basal diameter and presence of browse damage were recorded for each individual. Fallen logs and elk fecal pellet groups were counted along the same transects. Aspen seedlings were heavily browsed throughout the study area and were less likely to be found near high-elevation meadows. Variation in elk pellet densities was not explained by the density of logs at the scale of the transect or the site. The height of aspen seedlings was not related to density of logs, pine saplings or elk fecal pellet groups. However, taller aspen were found at higher elevations and with more open meadow in the landscape. This suggests that later snowmelt and alternative forage may reduce browsing pressure on aspen. Given that some of the sites had densities of pine saplings in excess of 60,000 stems ha^-1 and densities of downed logs greater than 2000 logs ha^-1, these results suggest that fire-induced coarse wood and pine saplings will not create broad-scale browsing refugia for aspen in the landscape of the Yellowstone plateau.