Differences in avian community structure and biodiversity following a Sudden Aspen Decline in Southwest Colorado

Aspen (Populus tremuloides) stands in southwestern Colorado have recently experienced sudden aspen decline (SAD), which is the rapid mortality of aspen forest on a landscape scale. Studies on bird populations indicate higher avian biodiversity associated with aspen habitat; yet, no research has been published on avian community changes associated with SAD. Therefore, from early June to early July 2009 and 2010, we conducted avian surveys and evaluated SAD intensity in aspen stands located in the Dolores Ranger District of the San Juan National Forest. We classified different SAD levels that included: 1) Low SAD (0-30%), 2) moderate SAD (30.170%), and 3) high SAD (70.1-100%). We evaluated avian species richness and diversity among different SAD levels, performed an indicator species analysis, and analyzed use of SAD habitat by foraging guilds. Avian species richness and diversity was significantly greater in stands with high SAD than in stands with low SAD. Similarly, the greatest number of indicator species, species that are particularly faithful to a SAD level, was associated with high SAD in 2009 and 2010. Also, obligate insectivores and species with diets composed of > 75% invertebrates were more abundant in high SAD than in low SAD. Our data suggests that the initial changes in avian community structure associated with SAD are distinct between low and high SAD stands, and that stands experiencing high SAD support greater avian biodiversity during the early stages of this disturbance due to forest structure changes in aspen overstory and potential new food sources.