Recently there has been concern about the conservation status of mahogany ( Swietenia spp. ) in the Neotropics. Thus there is a need of more information on its growth characteristics in different environments and genetic composition. A reciprocal transplant study begun in the 1960’s by the USDA Forest Service of different populations and species of mahogany is being used to address some of these issues. Seed was harvested from a series of populations in Central America and the Caribbean. Seedlings from these populations were planted in Puerto Rico and the Virgin Islands, across an array of environments ranging from dry to wet forest. Trees were periodically measured from 1965 to 1993. The objectives of this analysis of the resulting data were to 1) assess the relative amount of phenotypic plasticity and genetic variation 2) assess the segregation of genetic variation among species, among populations, and within populations, and 3) to examine how provenance and species growth characteristics change across different environments. Several findings will be presented. 1) Species of mahogany were genetically distinct in growth characteristics. 2) More genetic variation occurred among than within populations 3) More variance in growth characteristics was explained by genetic differences among species than by environmental variation among plantation sites, which in turn explained more variance than genetic differences among populations. 4) Species and several populations showed distinct responses to wet and dry environments in Puerto Rico. These findings have implications for the conservation biology of these species, including strategies to preserve genetic variation.

Key words: conservation biology, genetic variation, phenotypic plasticity, reciprocal transplant experiment, Swietenia spp., tropical botany