Aspen heart rot fungus (<i>Phellinus tremulae</i>) distribution in aspen forests in relation to open meadows: implications for red-naped sapsucker (<i>Sphyrapicus nuchalis</i>) nesting habitat

Abstract

Red-naped sapsuckers (Sphyrapicus nuchalis) are an integral part of the aspen (Populus tremuloides) ecosystem in the montane western U.S. They are a double keystone species, providing both shelter and nutrients to a variety of organisms within the system. Numerous studies have documented the importance of fungal infection in nest site selection by woodpecker species. Aspen heart rot fungus (Phellinus tremulae) is extremely important in nest site selection in red-naped sapsuckers. To gain an adequate understanding of the dynamics of the fungus and its influence on the cavity-nesting complex, this study aims to understand the relationship between fungal density and distance to open meadow. Stands of aspen within the vicinity of the Rocky Mountain Biological Laboratory, CO, USA were selected based on similar slopes and accessibility. Fifty transects ranging from 30m to 100m were run across elevational gradients from meadows into the interior of aspen stands. Number of trees, fungal presence, and sapsucker damage was recorded along each transect. Total fungal density and fungal density in trees >17cm DBH were negatively correlated with distance from edge(τ=- 0.1296, p=0.0073; τ=-0.1264, p=0.0095, respectively), suggesting an effect of edge on the occurrence of fungus. Possible causes of increased fungal density at edges include increased wind dispersal mediated by complex three dimensional flows within stands, as well as increased pruning and therefore open wounds, due to high velocity and common occurrence of wind at stand edges. Further studies need to be done on the dispersal dynamics of the fungus in order to gain a full understanding of it's complex effects on the aspen ecosystem.