Points of reference in the assessment of change in vegetation and land condition.

Abstract

An analysis is made of the selection and application of reference areas in the derivation of indices of range condition. In presentusage there are deficiencies arising from bias in reference area selection, the absence of correction for natural variation, the designationof 'climax' as 'best' and the choice of grazing pressure as the only gradient of vegetation change.A system of nlultiple reference areas is proposed, based on a sampling of land units and the analysis of the principle vectors contributingto vegetation change. These areas would be chosen ;IS a statisticai sample of the land unit they represent and the calculationof indices of difference or change would be corrected for errors arising from natural variatio~i and measurement error. Reference areaswould be chosen on the basis of their potential productivity in terms of the principal land use.