Introduction

Forests are found in tropical, temperate and boreal zones. Most of these forests contain multiple species of flora and fauna, but the number of species generally increases towards the Equator. Many tropical forests have a bewildering variety of trees and other plant species, and their faunas are equally diverse.

In this module we will examine this diversity and how it is measured (Topic 1). Measuring species richness is extremely difficult when there are a large number of very rare species, necessitating large sampling areas. In addition, many species are difficult to observe: they may be nocturnal or restricted to inaccessible parts of the canopy. In addition, many species, especially amongst the invertebrates, are still formally described.

In the second topic, we examine some of the many theories that have been put forward to explain the species richness of tropical forests. We focus on trees as it is the trees that provide much of the structural and compositional variety that enables so many other species to co-exist. However we also look at other taxonomic groups where appropriate.

In the third topic, we look at some rare and common species. Why are some species very rare, while others are very common? How to stands develop in tropical forests that are dominated by a single species of tree, and how does this affect the fauna?