View article

2.1 Introduction and Ecosystem processes emerge from the capture, transfer, and loss of energy nutrients by biological species. It has been clearly established that both the presence of particular species and also the total number of species involved can influence emergent ecosystem processes. Keystone species such as predators that prey selectively on competitive dominants or plants that fruit during seasons of scarcity can have profound effects on entire ecosystems and have been identified in a wide range of habitats from the rocky intertidal to tropical forests (Paine 1966; Terborgh 1986). In contrast, evidence that the total number of species present influences ecosystem functioning has been limited to laboratory microcosms (Naeem et al 1994) and to relatively species-poor grasslands (McNaughton 1993; Tilman and Downing 1994). In this chapter, the question is asked whether the total number of plant species present affects some components of ecosystem functioning in tropical forests. Tropical forests include the most floristically diverse habitats on the planet. Although it is well established that species richness influences processes in species-poor ecosystems, the effect of an increase from perhaps 50 tree species per hectare in a dry tropical forest to more than 300 tree species per hectare in wetter forest is uncertain. Uncertainty also remains over when, where, and how species composition affects ecosystem functioning.

This chapter addresses the relationship between plant species diversity and ecosystem productivity and stability. In the introductory chapter to this volume, Orians et al. provide a more complete catalog of ecosystem …