Quantification of Wood Habitat in Subtropical Coastal Plain Streams

Abstract

To assess the importance of woody debris in two relatively unaltered Coastal Plain streams in the southeastern United States, a line intersect technique, developed by foresters, was used to estimate volume, mass, surface area, and spatial distribution. The ash-free dry mass of in-channei woody material was 6.5 kg/m 2 of stream channel bottom in the sixth-order Ogeechee River and 5.0 kg/m 2 in the fourth-order Black Creek. Most wood is located near the erosional bank in these meandering streams. These wood mass estimates are much higher than expected for middle-order streams and are similar to those from several small headwater streams in other regions. Due to their very low slopes (<0.02%), these streams appear to have insufficient stream power to move large woody material. Snag, or woody, habitat is the major stable substrate in these sandy-bottomed streams and is a site of high invertebrate diversity and productivity. In-channel snag surface area per square metre of channel bottom was 0.249–0.433 m 2 in the Ogeechee and 0.191–0.379 m 2 in Black Creek, depending on the hydrograph stage. With invertebrate biomass of 6.6 g dry mass/m 2 of snag surface, this results in an invertebrate biomass of at least 1.88 g/m 2 of channel bottom. Wood is also important to fishes, providing a rich source of invertebrate food, habitat, and cover. In addition to its obvious biological role, wood enhances the ability of a stream to process and conserve nutrient and energy inputs and has a major influence on the hydrodynamic behavior of the river. The quantification of wood habitat seems mandatory to assess past or potential impacts of snag removal on ecosystem processes in low-gradient streams.