Influence of woodland management within interior forests on foliage arthropods and avian insectivores

Eastern North American woodlands have become rare and degraded by land use conversion and fire suppression, which prevents regeneration of oaks and other shade-intolerant species. The persistence of woodlands now hinges on management using prescribed fire and tree thinning. Simultaneously, most contiguous forests have been lost to deforestation and fragmentation. Converting patches within these forests into woodlands could support a diversity of bird species, but may deter those needing mature forests, creating a potential trade-off. In a three-year field study in the Midwestern USA, we examined the effects of woodland management within interior forests on foliage arthropod biomass, and insectivorous bird species richness and mass-abundance relationships, which describe the energetic limit of a community. Mass-abundance relationships are considered integral to ecological communities and, in ecosystems without anthropogenic threats, typically show a negative relationship between species’ body mass and their abundance because of higher energy requirements for larger species; deviations indicate biodiversity responses to habitat disturbances. Working in two managed and two unmanaged woodland sites from 2021 to 2023, we conducted 3809 arthropod branch surveys, captured, banded, and weighed 535 insectivores of 32 avian species, and documented 43 insectivores on point counts. We found that foliage arthropod biomass was higher in managed sites during 2021 and 2022 but not 2023, and that managed woodlands supported higher richness of understory insectivores, all insectivores, and early-successional species, and equal richness of ground foragers and mature forest specialists. The insectivorous bird community in managed sites had significant negative mass-abundance upper bounds limits in all years, while in unmanaged sites this relationship was nonsignificant and appeared to vary widely between years, potentially reflecting differences in arthropod resource availability. Thus, although the anticipated trade-off between woodland management and mature forest bird conservation was not strongly evident, the inconsistent mass-abundance relationships in unmanaged sites suggest lower resilience to resource variability.