Vegetation responses to helicopter and ground based logging in blackwater floodplain forests

Logging in floodplains of low order, blackwater streams may damage existing seedlings and rootstocks, and create soil conditions that inhibit establishment and growth of regeneration after harvest. Removal of logs via helicopters has been advocated to minimize soil damage and facilitate rapid revegetation. We tested impacts of helicopter Versus conventional skidder harvest systems on regeneration, woody plant community structure and biomass growth in three blackwater stream floodplains in southern Alabama. The helicopter treatment resulted in significantly greater woody plant density (19,900 versus 14,300 stems/ha by Year 8), but both treatments were well-stocked with commercially valuable species. By Year 8, treatment effects on density of individual species were generally not significant; however, density of Cliftonia monophylla was lower on skidder plots (p=0.001) and density of Nyssa sylvatica var, biflora was lower on helicopter plots (p=0.092). In both treatments, species richness within 0.004 ha regeneration plots declined slightly between pre- and post harvest, but the Shannon diversity and evenness indices remained essentially unchanged through 8 years after treatment. Post-harvest survival of Acer rubrum, Cyrilla racemiflora and C. monophylla rootstocks was significantly lower on the skidder plots. In both treatments, species dominant before harvest remained so afterwards. Species with the tallest sprouts in Year 8 were Liriodendron tulipifera, Magnolia virginiana, and A. rubrum. During the first 2 years after logging, aboveground biomass was greater in the helicopter treatment, but the difference was only significant in Year 1. We conclude that both harvesting methods had little effect on species composition. Skidding may result in a stand structure more favorable for commercial timber production; however, impacts of skidding on long-term productivity are not yet known. (C) 2000 Elsevier Science B.V. All rights reserved.