Responses of bat-prey to prescribed burns and mechanical thinning

Abstract

Insects are an important aspect of forest and woodland ecosystems due to their role as prey for vertebrate species. Our research investigated the relationship between insects and forest management practices in the Ozark National Forest in Arkansas. We looked at the differences in biomass, abundance, and diversity of insects in 30 treatment stands with varying burn frequencies. Twelve of these stands were burned and mechanically thinned, 12 were only burned, and 6 were untreated. The burn frequencies of these stands range from being burned 0–4 times from 2007 to 2018. We deployed blacklight traps in each of the stands every month from mid-March to mid-November in 2019 to assess nocturnal bat prey. Over 30,070 insects were collected, with Lepidoptera being the most abundant order. Insects were dried, weighed, and identified for diversity metrics. We used multi-model selection and AICc to find the top models from a series of linear mixed effects models to determine the best forest management strategies for bat prey. Total nocturnal, aerial insect biomass, Lepidoptera biomass, and Macroheterocera abundance was lower in thinned stands. However, it is unclear if it is the removal of Lepidoptera tree hosts or changes to bat foraging activity that drove this relationship. Stands burned at high frequencies had a higher abundance of Coleoptera. The intermediate disturbance hypothesis was not supported with regards to Lepidoptera diversity and burn frequency. Burning at high frequencies (4 times per 12 years) and not thinning may be the best strategy for maximizing nocturnal Coleoptera and Lepidoptera, respectively.