15 - Restoring the functions of grazed ecosystems

Summary

INTRODUCTION

Since the Neolithic, human populations have expanded across the globe, changing the landscape through fire, forest clearance, hunting and the grazing of domestic stock (Van Wieren 1995, see also Chapter 7). As a consequence the majority of the terrestrial ecosystems of the globe are man made, dominated by large herbivores, be they domestic or wild. Today, over 50% of the global land surface is managed for livestock grazing and other large expanses supporting wild herbivores, with up to 20% of the land area put over to nature conservation in some countries (e.g. Cumming 1998, Olff et al. 2002). Large herbivores are major drivers of the shape and function of terrestrial ecosystems modifying nutrient cycles, soil properties, net primary production and fire regimes. Whilst these impacts can be positive for ecosystem function, if grazing pressure is high, in the long‐term, changes in ecosystem structure and its effects on ecosystem function (e.g. accepting, storing and recycling water, nutrients and energy) can lead to a reduction in the ability of the ecosystem to provide goods and services, in which case the land is degraded. If degraded ecosystems are to fulfil their potential in the economic, aesthetic and cultural landscape there is a need to restore their functioning through changes in management and land use. Some of these changes may be minor, e.g. changes in the densities of herbivores, others may be more dramatic, for example, restoration of predators or reductions in soil nutrient levels, through the removal of topsoil.