Influence of Wildfire Disturbance and Post-Fire Seeding on Vegetation and Insects in Sagebrush Habitats

Disturbance events alter community composition and structure because of differences in resistance and resilience of individual taxa, changes in habitat resulting in colonization by new taxa and alteration of biotic interaction patterns. Recent changes in disturbance types, frequencies and intensities caused by anthropogenic activities may further alter community composition and structure if these disturbances exceed the tolerances or adaptations of some taxa. In sagebrush steppe habitats of the western United States, wildfire is the current dominant disturbance type, burning millions of hectares annually. Further, up to 90% of sagebrush-steppe ecosystems are affected by anthropogenic influences such as invasive species. Post-fire seeding treatments are widely used to reduce soil erosion, control the establishment of invasive plant species, and restore habitat for wildlife. We investigated insect community responses to wildfire and post-fire seeding in sagebrush-steppe habitats in southwestern Idaho by comparing insect communities among three condition classes (hereafter treatments): burned-and-seeded (BS), burned-and-unseeded (BX), and unburned (UX), which served as a control. We also quantified indirect effects of treatments on insects by assessing vegetation composition and structure (height) differences among these treatments. We found post-fire seeding changed the vegetation composition at BS plots compared to the BX plots by increasing the amount of seeded bunchgrasses and forbs, but these seeding efforts did not achieve the vegetation composition of UX plots because sagebrush was not successfully re-established. We found evidence to suggest that differences in vegetation among treatments affected the composition of insect assemblages. The strongest difference was between UX and burned (BS and BX) plots, but we found some evidence that insect communities were influenced by vegetation differences between BS and BX plots when UX plots were removed from the analysis. Correlations between insect families and vegetation variables provide useful information for evaluating potential effects of shrubland fires on insects and how best to support their post-fire recovery. This information could be useful to assess the potential for recovery of insect assemblages to various disturbance types, which could in turn inform the development of ecological models to potentially predict the threshold of tolerance for functional groups of insects to disturbances