Forest disturbance and arthropods: Small-scale canopy gaps drive invertebrate community structure and composition

In forest ecosystems, disturbances that cause tree mortality create canopy gaps, increase growth of understory vegetation, and alter the abiotic environment. These impacts may have interacting effects on populations of ground-dwelling invertebrates that regulate ecological processes such as decomposition and nutrient cycling. A manipulative experiment was designed to decouple effects of simultaneous disturbances to the forest canopy and ground-level vegetation to understand their individual and combined impacts on ground-dwelling invertebrate communities. We quantified invertebrate abundance, richness, diversity, and community composition via pitfall traps in response to a factorial combination of two disturbance treatments: canopy gap formation via girdling and understory vegetation removal. Formation of gaps was the primary driver of changes in invertebrate community structure, increasing activity-abundance and taxonomic richness, while understory removal had smaller effects. Families of Collembola and Diplopoda, as well as some families of Coleoptera, increased in combined canopy and understory disturbance treatments, whereas Curculionidae and Nitidulidae were more abundant in undisturbed forest. Gaps increased light availability, height and cover of understory vegetation, and soil moisture levels, and decreased depth and cover of leaf litter compared to undisturbed forest. Decoupling of canopy and understory vegetation disturbances revealed gap formation as an important short-term driver of ground-dwelling invertebrate community structure and composition. Our findings increase understanding of how ground-dwelling invertebrate communities respond to disturbance and inform sustainable management of forest ecosystems to foster biodiversity and resilience.