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

Abstract

Thirty-five years post-harvest, effects of harvest disturbances upon tree composition and aboveground biomass were evaluated in a water-tupelo (Nyssa aquatica)- baldcypress (Taxodium distichum) bottomland. The forested wetland, 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 herbicide application (glyphosate) to sprouts and seedlings for two years (GLYPH). Thirty-five years post-treatment, species, diameter at breast height (DBH; 1.37 m or above swell) and tree height were measured within treatments and converted to aboveground dry weight biomass. Clip plots were installed for herbaceous and woody stems < 1.37 m. Density and biomass results indicate HELI and SKID are on a trajectory to produce species, densities and biomass similar to REF. GLYPH coppice and seedlings were removed, so GLYPH regenerated from seedbanks and flood disseminated seed. GLYPH has transitioned from an herbaceous freshwater marsh to an open woodland/savanna community. GLYPH exemplifies advantages of coppice for rapid tree regeneration and growth on sites with long hydroperiods. This research demonstrates the capacity for long-term recovery of forested wetland ecosystems following harvest where multiple site/stand factors favored recovery. Adequate stocking of flood tolerant species capable of stump sprouting favored survival of original species. Floods provided annual sediment deposits to offset rutting. Compaction was additionally ameliorated by shrink-swell clays. Finally, nearby forests provided seed sources for areas. Collectively, these factors favored rapid recovery from disturbances.