Indicators and thresholds for the evaluation of sustainable land management

Within the context of major land uses such as agriculture, the indicators of sustainability must be framed within the social and economic conditions of the society in question. Whereas an indicator is used to measure changes in key attributes, usually over time, a threshold provides a baseline against which sustainability can be assessed. A direct measure of sustainability using indicators is difficult, and indirect measures or surrogates may be easier to establish. There is some information on threshold values for indicators, particularly for indicators such as soil acidity and nutrient status, and for those relating to root physiology. Because some threshold values are soil specific, it seems likely that range of values will be required for a particular indicator. There have been few case studies involving indicators and thresholds for sustainable land management. Examples of soil and land suitability for the production of Hevea brasiliensis (rubber) in Malaysia and for the management of sloping lands for annual crops in the Philippines are discussed. Biophysical indicators and thresholds for sustainable rubber production appear to be reasonably well-understood, particularly those relating to climate and soil physical factors. For sloping lands in the Philippines, yield data and benefit: cost ratios give a clear picture of trends and sustainability.