Catchment-scale deer exclusion changes longitudinal patterns of macroinvertebrate communities through soil runoff mitigation

Deer overpopulation is occurring worldwide, and deer-induced soil runoff into streams increases levels of sus-pended sediment and fine sedimentation. While deer-induced fine sedimentation in depositional habitats including first-and fourth-order streams is known to alter macroinvertebrate communities, effects of drifting suspended sediment in erosional habitats between the stream orders are poorly understood. Here, habitat and macroinvertebrate community structures in first-to third-order streams were compared between deer-excluded and grazed catchments of a Japanese headwater system. Fine sediment cover on the streambed was significantly greater in the grazed catchments than the deer-excluded catchment only for first-order streams, while macro-invertebrate community structure differed distinctly between the deer-excluded and grazed catchments at all stream orders. Burrowing collector-gatherers, which inhabit fine streambed sediments, were less abundant in first-order streams in the deer-excluded catchment than the grazed catchments, while clinging collector-filterers, which are vulnerable to suspended sediment inputs, were more abundant in second-and third-order streams of the deer-excluded catchment than the grazed catchments. These results suggest that the effect of deer exclusion on stream ecosystems varies with longitudinal changes in sediment deposition and transport capacity. Hydro-geomorphological processes are thus fundamental to assessing the restoration of forest-stream ecosystems, particularly in spatiotemporally dynamic headwater systems.

Automated summary

Deer overpopulation globally leads to increased soil runoff into streams, resulting in higher levels of suspended sediment and fine sedimentation. While the effect of deer-induced fine sedimentation on macroinvertebrate communities in depositional habitats is known, the impact of drifting suspended sediment in erosional habitats remains unclear. This study compared habitat and macroinvertebrate community structures in first-to third-order streams between deer-excluded and grazed catchments in a Japanese headwater system. The results showed that fine sediment cover on the streambed was significantly higher in grazed catchments for first-order streams, while macroinvertebrate community structure differed between the deer-excluded and grazed catchments across all stream orders. These findings highlight the importance of hydro-geomorphological processes in assessing the restoration of forest-stream ecosystems, particularly in dynamic headwater systems.