Ecology provides a pragmatic solution to the maintenance of genetic diversity in sustainably managed tropical rain forests

Abstract

An important aspect of the sustainable management of tropical rain forests is the maintenance of genetic diversity within populations of commercial tree species. Logging may reduce genetic variation directly and may also affect genetic processes, leading possibly to genetic erosion and ultimately even species extinction. It is, however, impractical for the forest manager to make meaningful measurements of genetic variation and they are therefore inappropriate for use as indicators of sustainable forest management. We propose that the application of well-known silvicultural principles is the most practical way of preventing rapid loss of genetic diversity. Most tropical rain forest tree species have many more individuals below the minimum size for commercial exploitation than above. The genetic diversity of these species will be little affected by logging, as the stems removed form only a small fraction of the total population. Similarly, for most species, disruption of normal mating patterns will either not occur or be transient, because reproduction commences at sizes well below felling limits, or because, after logging, juveniles will be recruited to the sexually mature size classes. Strongly light-demanding species with a commercial value are most likely to suffer loss of genetic diversity from logging. Characteristically, these have populations in which only a small proportion of the total population lies in small size classes. In order to conserve genetic diversity, pre-felling silvicultural treatments will be required to increase the survival and growth of juveniles. Ecological and genetic research needs to focus on these light-demanding species.