Increased levels of forestry best management practices reduce sediment delivery from Middle and Lower Coastal Plain clearcut harvests and access features, southeastern states, USA

Abstract

Over 390,000 ha of forestland are clearcut annually (1–2%) across the Coastal Plain region of the southeastern U.S. where forestland occupies approximately 30 million hectares in the region. Extensive periods of high-water tables, wet-weather and harvesting, rutting, erodible soils, and drainage networks typical of the Coastal Plain increase the potential for erosion and stream sedimentation. To mitigate these impacts, water quality forestry Best Management Practices (BMPs) were developed for erosion and sediment control and are recommended and approved by all southeastern state forestry agencies for application during and after harvests. The goal of this study was to estimate erosion and sedimentation from silvicultural operations in the Coastal Plain under three different and previously recognized levels of BMP implementation including BMP– (<80%), BMP-standard (80%–90%), and BMP+ (>90%), where 90% represents average implementation. A total of 35 recent clearcut sites were evaluated in the Coastal Plain of 12 southeastern states. Erosion was estimated via the USLE-Forest model at five operational features, including decks, stream crossings, haul roads, skid trails, and harvest areas only, which were classified into one of three BMP levels. Sediment traps were utilized on a subset of Coastal Plain sites in Virginia and North Carolina so that sediment delivery ratios (unitless) could be calculated. Clearcut area estimates were obtained from the United States Forest Service (USFS), Forest Inventory and Analysis (FIA) Program. The percent areas comprised within each operational feature were multiplied by total clearcut areas in the Coastal Plain region so that erosion and sedimentation estimates could be expanded to a regional scale. Examination of the different levels of BMP implementation revealed estimated sedimentation rates of 0.5 Mg ha−1 yr−1 and 0.4 Mg ha−1 yr−1 at the BMP-standard and BMP+ levels, respectively. The range of overall estimated sediment masses at the BMP-standard and BMP+ levels most accurately reflects the current state of BMP application in the Coastal Plain. BMPs were most obviously effective at mitigating erosion and potential sediment delivery from Coastal Plain skid trails and haul roads. The highest level of BMP implementation (BMP+) at forest roads and skid trails mitigated approximately 95% of sediment compared to BMP–. Overall sediment removal efficiencies were 77% for BMP-standard and 83% for BMP+ respectively when compared to BMP–. Conclusively, this study demonstrates that forestry BMPs are highly effective at mitigating erosion and stream sedimentation when appropriately applied in the southeastern Coastal Plain.