Consequences of plantation harvest during tropical forest restoration in Uganda

Timber plantations have recently received considerable attention as a forest restoration strategy for heavily degraded lands in the humid tropics. Plantations can facilitate secondary forest regrowth by providing an understory environment more favorable for native plant recruitment than unmanaged degraded habitats. To better understand secondary forest development and to evaluate plantation use as a restoration strategy, we studied natural forest succession after plantation harvest in Kibale National Park, Uganda. We asked four questions concerning using plantations as a restoration tool. How does timber harvest affect forest succession? How does initial on-site recruit availability (e.g., seeds, seedlings) after logging influence successional pathways? How easily can forest succession be enhanced through intervention? How does using exotic timber plantations to restore forests compare with fire exclusion as a restoration strategy? Timber harvesting killed or severely damaged many native stems, hindering subsequent forest regrowth. Despite this setback, native stem densities 4-6 years after logging equaled or surpassed native stem densities in unlogged plantations, suggesting timber removal accelerated forest succession. Successional habitats with high and low initial densities of on-site recruits first diverged in forest structure and composition, but then converged for many of these variables within 6 years of logging. Intervening to accelerate forest succession met with mixed results. Removing non-tree vegetation did not enhance tree establishment, growth, or survival after 2 years. However, leaving standing, dead timber trees as perches for seed-dispersing birds seemed to increase seedling establishment relative to control areas. Mortality and growth of seedlings planted into successional habitats 1-2 and 5-6 years after logging were similar, and predicting individual species responses based on successional status was unsuccessful. We compared succession in unlogged and logged (5-6 years after logging) plantations to a similar aged site where fires were excluded but no plantation species established. Our results suggest excluding fire is a better strategy for promoting forest succession than establishing then not harvesting plantations. Fire exclusion versus establishing then harvesting timber are comparable restoration strategies differentially enhancing tree sapling recruitment and growth, respectively. While forest regeneration was successful where fire was excluded long-term fire exclusion may be difficult, and several non-ecological challenges to using plantations exist (e.g., the conflict of managing for biodiversity versus timber production). In summary, our research suggests managers should carefully weigh the risks of using plantations or fire exclusion against other forest restoration strategies. (C) 2002 Elsevier Science B.V. All rights reserved.