Introduction

Within Australia we have the paradox of having a detailed understanding of the processes whereby our renewable resources are being destroyed or degraded but lacking a rigorous quantitative assessment of how much has been degraded and how severely, or whether this degradation is accelerating or stable. Nor are the costs known. We understand the detail clearly but have no overview. Unfortunately, it is the latter that is required for instigating changes in management to curb land degradation. Land degradation is taken here as the end result of any factor or combination of factors which damage the land, water or vegetation resources and restrict their use or productive capacity (see Chartres, Chapter 1).

The comprehensive and accurate overview is lacking for two reasons. The first is that we are dealing with a dynamic system of land in much of agricultural Australia; major changes in vegetation, soils and drainage associated with agricultural development are still occurring even though most of the agricultural lands have been occupied for a century or more. For example, extensive clearing of native vegetation for cropping in Western Australia and Queensland has occurred during the previous two decades, and is still in progress. It follows that many of the biological and physical changes due to European settlement have yet to stabilise, or worse still, many consequences of these changes remain unidentified.

Secondly, the scope and duration of scientific investigations of these problems have frequently been inadequate to allow firm conclusions to be drawn or management solutions to be developed for Australian agroecosystems.