INDICATORS AND THRESHOLDS FOR THE EVALUATION OF SUSTAINABLE LAND MANAGEMENT

Within the context of major land uses such as agriculture, the indicat ors of sustainability must be framed within the social and economic co nditions of the society in question. Whereas an indicator is used to m easure changes in key attributes, usually over time, a threshold provi des 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 infor mation on threshold values for indicators, particularly for indicators such as soil acidity and nutrient status, and for those relating to r oot physiology. Because some threshold values are soil specific, it se ems likely that range of values will be required for a particular indi cator. There have been few case studies involving indicators and thres holds for sustainable land management. Examples of soil and land suita bility for the production of Hevea brasiliensis (rubber) in Malaysia a nd for the management of sloping lands for annual crops in the Philipp ines are discussed. Biophysical indicators and thresholds for sustaina ble rubber production appear to be reasonably well-understood, particu larly 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.