The western edge of Yellowstone National Park (YNP) is one of North America's most striking borders between a natural landscape and a human-altered one. Within YNP, vast stands of centuries-old coniferous forest are broken only by paths of recent wildfires. Outside the park, numerous clearcuts fragment what forest remains. Yellowstone's old-growth forests and wildfire patches are rich in structural complexity, with many canopy layers, tree sizes, and/or abundant snags. West of the park, structural complexity has been greatly reduced by clearcutting and fire suppression. Most modern ecologists would predict that the structural complexity in YNP supports a diverse community of animals and plants, while fewer native species are expected to occur in the human-impacted lands outside of the park. Science, however, is full of surprises.

When we sampled the bird community in this area, we found as expected that individual bird species differed in abundance among natural old-growth forests, wildfire patches, and clearcuts. However, bird species richness and total bird abundance did not dier among these stand types (Hansen and Harting, in prep). Moreover, bird density was low in all three stand types; only about 25% of what we had found in similar stands in western Oregon. Why is bird richness not strongly related to structural complexity in this landscape and bird abundance low compared with other biomes?

Nineteenth-century ecologists would likely not have been surprised at our observations in Yellowstone. They might have suggested that abiotic factors like topography, climate, and soil can exert a stronger influence on species than structural complexity.