Aspen snag dynamics, cavity-nesting birds, and trophic cascades in Yellowstone's northern range

We examined current and possible future aspen stand dynamics and cavity-nesting bird abundances for Yellowstone's northern ungulate winter range. Our measurements suggest aspen stands located within Yellowstone National Park (YNP) are in a different condition than those located in the Gallatin National Forest (GNF), immediately outside the park. Stands inside YNP were composed of more snags and had fewer small-diameter live stems than stands in GNF. Six of the 11 cavity-nesting bird species we analyzed were more abundant inside YNP where aspen snags were more abundant. We discuss potential implications of current and future aspen stand dynamics in the context of wolf re-introduction and trophic cascades for cavity-nesting birds. Our results suggest aspen stands within YNP will experience a relatively high abundance of snags in the near future, followed by a period of low snag abundance that will influence the abundance of several cavity-nesting bird species. The relative composition of future aspen stands within YNP will likely differ from historical conditions, and stands outside YNP, for several decades. (C) 2007 Elsevier B.V. All rights reserved.