Big-Leaf Mahogany is the most important commercial timber species of the tropics. Current debate concerning whether to protect it as an endangered species has been hampered by the lack of complete, definitive scientific documentation. This book reports on vital research on the ecology of big-leaf mahogany, including genetic variations, regeneration, natural distribution patterns and the silvicutural and trade implications for the tree.

Three-months old saplings from natural regeneration of mahogany around eight seed trees in the Ecuadorian Amazon were exposed to four different liberation thinnings. Mahogany survival was recorded 9 and 22 months later. Survival depended on thinning treatment as well as on pre-treatment sapling number. No influence of seed tree diameter, seed tree height, inclination, or orientation of slope, was found. Height growth of surviving saplings depended on thinning treatment, seed tree diameter, inclination and geographical orientation of slope. No influence of pre-treatment sapling number or seed tree height was found. The study indicates that silvicultural practices significantly influence the survival and growth of naturally regenerated mahogany. Provided a suitable management regime, it seems possible to sustain the next generation of mahogany from established natural regeneration. Results also suggest that removal of the understory significantly enhances survival of naturally regenerated mahogany. Other determinants of survival and growth are timing of the regeneration felling, gap size and the extent of herbal competition.

This thesis examines plant-enemy interactions in an unlogged population of big-leaf mahogany (Swietenia macrophylla King), a valuable but threatened Neotropical timber species. The Janzen-Connell mechanism predicts negative density-dependence in tree recruitment success and survival due to host-specific natural enemies in tropical forests. In Brazil, new seedlings and juveniles of this species are the sole putative hosts for caterpillars of a microlepidopteran herbivore (Steniscadia poliophaea Hampson). The Janzen-Connell mechanism was explored by testing its key prediction at both the scale of the individual and population level of S. macrophylla adults and by considering the influence of canopy cover on the mechanism's dynamics. One-year-survival of naturally established juveniles declined with increasing parent size and the local abundance of conspecific adults, whereas leaf damage and incidence of attack by the specialist S. poliophaea increased. An exclusion experiment indicated small mammals contributed to seed losses and also implicated S. poliophaea in lowering seedling recruitment near fruiting trees. A larger, separate experiment that also simulated seed dispersal confirmed the roles of vertebrates in seed mortality and S. poliophaea in the seed-to-seedling phase. Small mammals and S. poliophaea concentrated their attacks under the crowns of fruiting trees and in patches of clumped fruiters, leading to lowered recruitment by the end of the first growing season near parents and where conspecific adult density was higher. Canopy gaps influenced S. macrophylla susceptibility to these two enemies, and interacted synergistically with dispersal distance to enhance seedling survival. Simulated herbivory reduced the growth rates of juveniles in gaps, but did not affect their immediate survival over 8 months. Greater canopy openness, however, did increase the spatial scale of attack by S. poliophaea well beyond where seeds typically land. Herbivory on gap juveniles also increased with increasing conspecific adult density, but only in the early-wet season. A short-term seed addition experiment revealed little evidence for enhanced early post-dispersal performance on mahogany's preferred soil type in the region. Collectively, these finding suggest that small mammals, and more importantly, S. poliophaea caterpillars, are significant factors limiting the regeneration of big-leaf mahogany in natural forests, and are interpreted as support for the Janzen-Connell mechanism.