Response of stream macroinvertebrate communities to forest harvesting in the Piedmont region of North Carolina

Abstract

Forest disturbances have significant effects on water quality and quantity, river geomorphology, and the ecology of receiving waterbodies. Riparian forests provide numerous functions for aquatic communities including retaining fine sediments and nutrients, controlling water temperature, and providing food sources and habitat for aquatic organisms. Forestry Best Management Practices (BMPs) use riparian forests as buffers to mitigate potential sources of disturbance to aquatic ecosystems from forest management. The objective of this study was to quantify the impacts of timber harvest on stream macroinvertebrates in the Piedmont region. We assessed the changes in macroinvertebrate communities and identified their relationships with specific hydrologic and water quality parameters. We used a paired watershed approach to quantify the response of watershed hydrology and water quality to clearcut forest harvesting with the use of BMPs in the Hill Demonstration Forest and Umstead Research Farm in central North Carolina. We sampled macroinvertebrates and monitored water quality in the first-order streams, and surveyed vegetation within riparian zones one year preharvest (2010) and four years postharvest (2011–2014). We found more sensitive species (indicated by biotic index classifications), scrapers, and Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa from the harvested watershed than in the reference watershed at the Umstead Research Farm site. No differences were detected between the reference and treatment watersheds at the Hill Demonstration Forest site. More sensitive species were present in watersheds with the highest pine basal area and in-stream total organic carbon (TOC) loads. More scrapers were present in watersheds with low hardwood basal area, high stream flow, and more vines. EPT abundance was higher in watersheds with high stream flow, large pine trees, and thick leaf litter layer. EPT abundance was lower in watersheds with large hardwood trees and high TOC loads. Overall, sensitive species, scrapers, and EPT abundance were lower in the Umstead Research Farm reference watershed than in any other watershed. We conclude that, in contrast to similar studies in the region, clearcut harvesting with the use of BMPs did not cause detectable negative effects on macroinvertebrate communities. Moreover, water quality as determined by macroinvertebrates may even be improved in some cases following clearcutting. This study provides a better understanding of how macroinvertebrate communities in Piedmont streams change after harvesting and what watershed characteristics may be driving these changes. This information is useful in characterizing macroinvertebrates in headwaters in the Piedmont, and helps land managers protect aquatic resources across the region.