Comparing Cover-class Macroplot Data with Direct Estimates from Small Plots

Abstract

Recording canopy cover by class has been justified on the basis that it saves time and is less biased than direct percentage estimates. However, field workers tended to overestimate low cover and underestimate high cover when using cover classes on large plots when such estimates were compared to direct percentage estimates using small plots. Overestimation of low cover and underestimation of high cover took place three or four times as often as the reverse situation. Results from Monte Carlo simulations of changing canopy cover (20 and 30 To decrease of a dominant; 20 and 307o increase of a subdominant) showed that cover-class estimates can usually detect qualitative changes in mean cover, but provide biased quantitative estimates of changes in cover. The suggested causes were excessive and unequal class