Carbon pools and fluxes in a tupelo (Nyssa aquatica)-baldcypress (Taxodium distichum) swamp 24-years after harvest disturbances

Abstract

Bottomland forests are often productive ecosystems with large quantities of above- and belowground carbon, yet few long-term research projects relating to harvest effects in bottomland hardwood forests exist. This project evaluated the long-term (24-years after harvest) effects of three disturbance treatments on the carbon budget of a tupelo-baldcypress swamp in southwestern Alabama. The site was clearcut in 1986 and timber removed by helicopter. Disturbance treatments were: 1. helicopter (HELI), 2. skidder transportation simulation (SKID), and 3. glyphosate herbicide removal of vegetation following harvesting during years one and two (GLYPH). An adjacent portion of the original stand provides a non-harvested reference (REF) condition. Measurements included aboveground biomass, belowground biomass, soil carbon, soil CO2 efflux and estimates of buried coarse woody debris on the site. SKID treatments had the highest aboveground biomass (73.9 Mg ha−1) and total carbon storage (206.1 Mg ha−1) of the three treatments. GLYPH treatments had the lowest carbon storage (144.2 Mg ha−1) and lower aboveground woody biomass (26.4 Mg ha−1). HELI and SKID treatments were similar, but have slightly less in total forest carbon (168.7 Mg ha−1) than the REF condition. Belowground coarse woody debris storage increased carbon storage on these sites with an additional 8–13 Mg ha−1 being stored. GLYPH treatments had the highest total soil CO2 efflux followed by HELI and SKID treatments, respectively. Higher biomass and carbon storage of SKID treatments is explained by the flood tolerance of tupelo, diverse microtopography created by skidder traffic, and decreased soil aeration of skidder-rutted areas immediately after harvest which favored tupelo coppice.