The changing ecology of tropical forests

The threat to tropical forests is often gauged in terms of deforestation rates and the total area remaining. Recently, however, there has been a growing realization that forest can appear intact on a satellite image yet be biologically degraded or vulnerable to degradation. The array of direct threats to humid tropical forest biodiversity, in addition to deforestation, includes: selective extraction of plants; selective extraction of animals, biological invasion; fragmentation; climate change; changing atmospheric composition; and increasing tree turnover rates. The threats are linked to one another by a poorly understood network of causality and feedback effects. Moreover, their potential impacts on forest biodiversity are hard to assess because each threat is as likely to precipitate indirect effects as direct effects, and because several threats are likely to interact synergistically with one another. In spite of the uncertainties, it is clear that the biological health of tropical forests can become seriously degraded as a result of these threats, and it is unlikely that any tropical forest will escape significant ecological changes. Some groups of plants and animals are likely to benefit at the expense of others. Species diversity is expected to decline as a consequence of the changes in forest ecology. In the 21st century scientists and conservationists will be increasingly challenged to monitor, understand, prevent and head off these threats.