Observer differences in transect counts, cover estimates and plant size measurements on range monitoring sites in an arid shrubland.

Abstract

A field trial was held to test between-observer differences in recording counts and measurements made at range monitoring sites in grazed shrublands near Carnarvon, Western Australia. Ten pairs of observers worked independently to count perennials by species, t o measure major and minor axes of marked shrubs and to estimate foliar cover on fixed transects within three shrub communities. Following simple conventions, observers identified and counted shrubs by species with coefficients of variation (C.V.) < 10%, except where species identification or inconspicuousness of young plants led to particular difficulty. Errors incurred by a rapid field technique for shrub measurement averaged 5-9% C.V. for the major axes dimensions on a range of shrub forms, while the recording of second axis diameters was subject to two to three times as much error. Estimations of total projected foliar cover varied by 25% C.V. using a wheel point technique and by 30% using intercepts on line transects. Estimations of cover by species were more variable. The significance of these findings in planning appropriate techniques for monitoring arid shrublands is discussed.