Fire is a major driver of biodiversity and structural integrity in fire prone ecosystems. Due to fire suppression and pressure from climate change, fires are predicted to shift landscapes outside their historical range of variability, threatening the resilience of Ponderosa pine dominated landscapes in eastern Washington. In these landscapes, pollination can be critical for vegetation recovery post fire. Because pollination services can vary by species and across spatial and temporal scales, understanding the effect of fire on pollinator populations informs conservation management and ecosystem restoration efforts. In this study, we examined the effects of mixed fire severity on bee species abundance and diversity, and on the foraging success of the native blue orchard mason bee, Osmia lignaria Say (Hymenoptera: Megachilidae), and native cavity nesting bees. The study was conducted over two years in the Okanogan-Wenatchee National Forest in Chelan County, Washington, in forested areas that burned 1, 3-4, 6-7, and >10 years ago. Pollinator community composition, measured using blue vane and pan traps every two weeks from April to August, was predominantly driven by time since burn and fire severity. Pollinator abundance and diversity tended to be highest in areas that burned ~3-years ago and then decreased over time. Similarly, oviposition by O. lignaria was highest at sites that burned ~3 years ago, and lowest at sites that burned more than 10 years ago. This study provides important information for pollinator conservation and monitoring as managers work to restore fire prone landscapes.
