10 - Myccorhizas, succession, and the rehabilitation of deforested lands in the humid tropics

Summary

Introduction

Once covered by seemingly limitless forest, tropical lands today suffer escalating deforestation to satisfy the food, fuel and fibre demands of burgeoning human populations. Although disease and inaccessibility long protected the humid tropics – those tropical regions where annual precipitation exceeds potential evapotranspiration – deforestation is now rampant. Year-round warm temperatures and an excess of precipitation combine to exacerbate decline of soil fertility after deforestation. Diminished fertility and unacceptably low productivity, in turn, lead to evermore land clearing, such that, except for highly inaccessible areas of rugged terrain, strict national parks, and forest reserves, little undisturbed forest will remain by the end of this century (see Myers, 1991).

Utilization and conversion of humid tropical forests produces an extreme range of vegetations from largely intact forest matrix disturbed only by extraction of a few valuable timber species to barren, abandoned wastelands. As the latter predominate, rehabilitation of these highly degraded lands becomes a necessity. ‘Rehabilitation’ is used here to indicate the return of productive capacity to degraded land. With some types of land use, diminished primary production may be a consequence of disruption of mycorrhizal associations. In such instances, rehabilitation requires restoration of mycorrhizas.