SIMULATING EFFECTS OF LANDSCAPE CONTEXT AND TIMBER HARVEST ON TREE SPECIES DIVERSITY

Abstract

Although the need for implementing ecosystem management across bound- aries has been widely recognized, little is known regarding the extent to which loss of species richness resulting from timber harvesting in a focal forest could be offset by the surrounding areas. Using an individual-based, spatially explicit landscape simulation model (FORMOSAIC), which considers not only the dynamics of a focal forest, but also the interactions between the focal forest and the neighboring areas, we found that tree species richness of a tropical forest was related to the interactions between harvest impacts and immigration from adjacent areas. Simulation results indicated that adjacent species-rich forests increased species richness in a focal forest, but neighboring single-species planta- tions had opposite effects, and these effects were enhanced by the duration of immigration. Heavier harvest impacts on residual trees resulted in lower species richness, although the negative effects were partially offset by immigration from species-rich forests. Immigration after heavy harvest impact led to higher species richness than did immigration before harvesting, when the surroundings were species-rich forests. Harvesting on the edges of a focal forest resulted in higher species richness than harvesting at the center when seed dispersal distances were short, but spatial patterns of harvesting caused no differences in species richness if seeds could disperse into the focal forest from more distant sources. Under the option of no harvest, immigration was more important at small spatial scales than at large spatial scales. From the simulations, we also noticed some unexpected results. For example, heavy harvest impacts reduced a higher percentage of timber species than nontimber species. Simulation results from this study could provide insights into identi- fication of alternative methods for sustainable timber production and conservation of tree species richness beyond natural, management, and ownership boundaries. One potential method would be to establish a species-rich seed zone around a focal forest to partially compensate for negative harvest impacts. Another option would be to harvest timber trees at optimal locations and during optimal periods of time to accommodate dispersal ability and availability of seeds from the surroundings.