Assessing the power of the point-line transect to monitor changes in plant basal cover

Abstract

To assess the power of point data (collected systematically at each meter along a permanently-situated, 100-m line transect) to detect actual changes in plant basal cover, we developed a computational approach whereby a simplified shortgrass steppe community was spatially simulated on a computer screen. Cover was then reduced using a random disturbance pattern. One transect could detect an actual decrease in cover from 12% to 8% with less than 20% probability, while 5 transects increased this power to about 80% (P less than or equal to .05). A reduction in cover from 12 to 6% could be detected with 80% probability with only 2 transects, while a cover reduction to 10% could only be detected with 40% probability using 10 transects (P less than or equal to .05). Artificial populations provide a valuable mechanism for quantitatively evaluating field sampling designs.