The influence of post-wildfire logging on forb and pollinator communities and forb reproductive sucess, Gallatin National Forest, Montana

Abstract

Pollinators are in decline worldwide, and these declines have implications for flowering plants and their reproduction, given that 80% of flowering plants depend on insects for pollination. One potential contributor to pollinator species' declines is shifts in disturbance regimes, such as increased severity and frequency. Wildfires are essential natural disturbances that are important drivers of forest biodiversity in the western U.S., and there is often pressure to respond to wildfire with management including post-wildfire logging. This management strategy involves the removal of dead trees for economic value immediately following wildfire. Thus, is expected that post-wildfire logging has additional impacts on forest communities compared to non-salvage logging, and that it impacts forb and pollinator communities. Several studies have examined the short-term responses of forb and pollinator communities to wildfire and non-salvage logging individually, and one study examined their combined effects. However, no studies have examined the long-term effects of post-wildfire logging, on forb and pollinator communities and on forb reproduction. My research addresses these gaps in knowledge and asks: 1) how do floral and bee communities respond to post-wildfire logging and how do their responses differ between two different-aged fires, and 2) how does post-wildfire logging influence forb reproduction and pollen limitation of reproduction in an older wildfire? In the more recent fire, floral and bee density and species richness were higher in logged than unlogged areas. By contrast, in the older fire, forb and bee communities were similar between logged and unlogged areas. Unexpectedly, we found large inter- and intra-annual variation in the effects of post-wildfire logging. Lastly, in the older fire, there were no effects of post-wildfire logging on forb reproduction, but plants were pollen limited in unlogged areas. This suggests that plants in unlogged areas are able to augment their reproductive output with supplemental pollen resources, but plants in logged areas cannot. Together, these results suggest that post-wildfire logging is beneficial for forbs and pollinators in the short-term, and these positive effects depend on time of growing season and sampling year. However, post-wildfire logging may be detrimental for forb reproduction in the long-term.