Thirty-five-year timber harvesting disturbance effects on composition and biomass of Nyssa-Taxodium forested wetlands, southwest Alabama, USA

Abstract

Abstract Thirty-five years post-harvest, effects of harvest disturbances upon tree composition and aboveground biomass were evaluated in a Nyssa aquatica (water-tupelo)-Taxodium distichum (baldcypress) bottomland. The study site, along the Tensaw River, is within the Mobile-Tensaw River Delta in southwest Alabama. Nine replications of four disturbances were evaluated: no harvest reference (REF), clearcutting with helicopter removal (HELI), HELI combined with skidder extraction simulation (SKID), and HELI combined with broadcast spray (glyphosate) of sprouts and seedlings for two years (GLYPH). Thirty-five years post-treatment, species, diameter at breast height (DBH; 1.37 m) and total tree height were measured at monumented sample plots and converted to aboveground biomass. Clip plots were installed for herbaceous and woody stems shorter than DBH. Results indicate that HELI and SKID treatments remain on a trajectory to produce species composition and volume similar to REF. GLYPH lacked adequate coppice regeneration and regenerated from seedbanks and flood and wind disseminated seed, thus the treatment has succeeded from an herbaceous freshwater marsh to an open woodland/savanna community. The GLYPH treatment emphasizes the importance of coppice for rapid tree regeneration and the need for coppice success on sites having altered hydrology. This research further demonstrates the capacity for long-term recovery of forested wetland ecosystems following harvest. Furthermore, several site/stand factors favored stand regeneration, including adequate initial stocking of species capable of stump sprouting, intact hydrology with annual sediment deposits, shrink-swell soils, nearby seed sources and flood tolerances of original species acted collectively to favor rapid recovery from both HELI and SKID disturbances.