COS 37-5
Responses of plant and pollinator biodiversity to wildfires across a productivity gradient in the Northern Rockies
Wildfires are increasingly important disturbances in ecological communities, yet we lack a synthetic understanding of how complex networks of species interactions respond to these disturbances, especially at the large spatial scales most germane to conservation and management in naturally heterogeneous landscapes. Across a large-scale gradient of net primary productivity in Montana, we are studying how the local diversity (alpha diversity) and spatial variation in the community composition (beta diversity) of plant and pollinator communities and their interactions are influenced by mixed- and high-severity wildfires. Using a natural chronosequence of wildfires, we sampled plant and pollinator communities and their interactions along transects within wildfire perimeters that varied in severity and age as well as unburned controls. We expected that alpha- and beta-diversity of forbs and floral abundance, and thus pollinator diversity and abundance, would be highest in mixed-severity fires that occurred recently because of environmental heterogeneity that promotes resources important to both trophic levels. We also hypothesized that wildfires would have the strongest negative effects in low-productivity areas, resulting in less diverse and more homogeneous communities relative to high-productivity areas.
Results/Conclusions
For three plant functional groups (woody, forb, graminoid), fire severity interacted with productivity to drive species richness. However, the magnitude and direction of this interaction differed among plant functional groups. Forb species richness in unburned controls increased consistently along the productivity gradient, whereas both mixed- and high-severity fires had positive effects on forb species richness in low-productivity areas and negative effects in high-productivity areas. Mixed-severity fires supported the greatest floral density and beta-diversity of forbs. By contrast, preliminary analyses suggest that bee pollinator species richness was highest following high-intensity fires, particularly in areas of low productivity. Time-since-fire was also important for forb and pollinator communities: contrary to our expectations, “old” fires (25-30 years ago) supported the highest forb diversity and floral density compared to “new” fires (5-10 years ago) and unburned controls, whereas bee pollinator abundance and diversity was highest in “new” fires. These results suggest that interlinked trophic levels follow different successional trajectories following fire, likely influencing plant-pollinator interactions and pollination services.