Silviculture enhances the recovery of overexploited mahogany Swietenia macrophylla.
Abstract
Big leaf mahogany Swietenia macrophylla is the most valuable timber species in the tropics but its future as a commercial timber species is at risk. This study evaluates whether recovery of overexploited mahogany populations is enhanced by actively managing the species and its surrounding forest. We assessed the effect of four different management interventions that varied in their intensities of harvesting and silvicultural treatments. We tested the hypothesis that intensive forest management stimulates population growth rates. Data were gathered over a 4-year period in the plots (326 ha) of the Long Term Silvicultural Research Program in Bolivia. Plants >1.3 m tall were identified and monitored in the plots, while seedlings and saplings (<1.3 m tall) were recorded and measured around 58 adult mahogany trees. Population growth rate was simulated using population matrices based on observed vital rates. The application of silvicultural treatments only had an effect on seedling and sapling survival; survival being lowest in the unlogged forest and highest at intermediate levels of treatment application. Growth of larger trees tended to increase with management intensity, and was dependent on crown position and liana infestation. Removal of lianas and other competing trees had a positive effect on growth rates. Model simulations suggested that the recovery of overexploited mahogany population is enhanced by the application of intermediate levels of silvicultural treatments. Recovery is dependent on the retention of large seed trees (>70 cm diameter at 1.3 m height) that produce large numbers of seedlings. Harvesting simulations indicate that mahogany populations can only be sustainably harvested by increasing the cutting cycle length, reducing harvesting intensity and by maintaining optimal growing conditions. Synthesis and applications. Mahogany is the most valuable timber species in the tropics, and its range has dramatically decreased mostly due to commercial harvesting. The results of simulation modelling based on field and experimental data suggest that overexploited populations are recovering and that sustainable harvesting will be possible in the future when cutting cycle length is increased, harvesting intensity is reduced and silvicultural treatments are applied regularly throughout the cutting cycle.