A Comparison of Methods of Estimating Plant Cover in an Arid Grassland Community

Abstract

The area of ground covered by the aerial parts of plants has proved a valuable measure of vegetation and its changes. In the study of pastures either the total crown area or the basal area of tussock grasses is used. Generally the area is considered as the projection of the plant onto a horizontal surface or one at 450 to the ground, and is expressed as a percentage of the total area. Pasture research has led to the development of a large variety of methods for estimating percent cover; these have been collated by Brown (1954). The methods fall into four basic categories, depending on the type of observation made and the dimensions of the sampling unit (termed a quadrat sens. lat.). The categories are charting, ocular estimates, line intercept and point methods. Some recent attempts have been made by range workers in the U.S.A. to compare methods. Whitman and Siggeirsson (1954) found that the line transect method gave significantly lower estimates of cover than did a point method in mixed grassland. Johnston (1957) found small differences between the line intercept and point methods, though the former gave lower values. Heady, Gibbons and Powell (1959) obtained the same estimate of cover using a charting technique, line intercept and point methods in shrubland, and