Introduction

Rangelands are defined as natural or semi-natural areas that produce plants grazed by wild and domesticated animals (Stoddart et al., 1975). Included in this definition are unimproved grasslands, savannas, shrublands containing both grasses and woody plants, and hot and cold deserts (Fig. 13.1). These ecosystems occur on every continent except Antarctica and cover over 40%

©CAB International 2000. Climate Change and Global Crop Productivity (eds K.R. Reddy and H.F. Hodges)

| Cold winter deserts/semi-deserts ^ Temperate grasslands

| Warm (hot) deserts/semi-deserts |jg§ Tropical grasslands and savanna

Mediterranean grasslands and woodlands Q Other than rangelands Fig. 13.1. Distribution of the world's rangelands. (Redrawn from Allen-Diaz, 1996.)

©CAB International 2000. Climate Change and Global Crop Productivity (eds K.R. Reddy and H.F. Hodges)

of the terrestrial land surface, with the greatest area in Africa and Asia (Allen-Diaz, 1996).

Environmentally determined rangelands are found where climate (chiefly water balance and minimum temperature) and soils interact to prevent occupation by dense stands of trees. Human activities, broadly classified as land use patterns, are another major determinant of the composition and structure of rangelands, and are an example of the alterations to earth considered here as global change. Land use changes include manipulation of fire regimes and other natural disturbances, adjustments in the intensity and duration of grazing, and fragmentation of once continuous rangelands by intensive agriculture and urbanization. Global change also includes changes in atmospheric composition, e.g. carbon dioxide concentration ([CO2D and resultant modifications in climate (temperature, precipitation). Some aspects of global change, like atmospheric and land use change, are well underway. Others, including shifts in climate, appear imminent.

Anticipated global changes could dramatically alter the extent and productivity of rangelands, but prediction and risk assessment are complicated by the diverse nature of these ecosystems and varied goals of managers (Campbell etal, 1996; Stafford Smith, 1996).

1. Rangelands include a variety of plant species and growth forms (grasses, herbs, trees, shrubs) that respond in different ways and at different rates to the environment and to management inputs.

2. Rangelands are spatially and temporally variable. This natural variability increases the difficulty of discerning effects of management from those of the environment and environmental change (Campbell et al., 1996; Stafford Smith, 1996).

3. Rangelands traditionally have been used to produce livestock, but these ecosystems provide other 'goods and services', including recreation, water and fuel wood (Fig. 13.2). Atmospheric and climatic change, combined with social, economic and demographic forces, will influence the product or combination of products for which rangelands are managed, and the intensity of future land use.

In this chapter, we review climatic and atmospheric changes expected during the 21st century and suggest some of the consequences of these changes for rangelands that are used primarily for grazing. Non-grazing uses of rangelands are briefly noted to illustrate reciprocal interactions between land use and climatic and atmospheric changes. Finally, we suggest management implications of global change.

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