|Seefeldt, Steven - Steve|
Submitted to: Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/27/2006
Publication Date: 3/15/2006
Citation: Seefeldt, S.S., Booth, D.T. 2006. Measuring plant cover in sagebrush steppe rangelands: A comparison of methods. Environmental Management. 37:703-711. Interpretive Summary: Currently there are no cost-effective and objective methods to measure vegetation in western rangelands. The purpose of this research was to determine if new methods were cheaper than and as good at measuring vegetation covers as visual estimation. At the United States Sheep Experiment Station visual estimation was compared to a laser point frame, two meter above ground level (AGL) digital imagery and 100 meter AGL digital imagery. Overall measures of vegetation cover did not differ among the methods, but there were differences in measures of vegetation cover in 11 of the 14 management units that made up the study. The laser point frame was as good as visual estimation for precision and cost. Two meter AGL was more precise than visual estimation and equivalent in cost. One hundred meter AGL was more precise and less expensive than all methods and it measured a 48 times as much area as the other methods. Both two and 100 meter AGL provided the user with permanent records of the vegetation, which could be used for other types of analyses or for monitoring change in vegetation due to management strategies. The reduction in cost per sample, the increased speed of sampling, and the increased precision associated with the 100 meter AGL digital imagery are compelling arguments for adopting this vegetation sampling method throughout western North American rangelands.
Technical Abstract: Methods that are more cost-effective and objective are needed to detect important vegetation change within acceptable error rates. The objective of this research was to compare visual estimation to three new methods for determining vegetation cover in the sagebrush steppe. Fourteen management units at the U. S. Sheep Experiment Station were identified for study. In each unit, 20 GPS locations were selected for measuring plant cover using visual estimation, laser-point frame (LPF), 2-m above ground level (AGL) digital imagery, and 100-m AGL digital imagery. In 11 of 14 management units, estimations of vegetation cover differed (P < 0.05). However, when combined, overall estimates of vegetation cover did not differ. Standard deviation, corrected sums of squares, coefficient of variation, and standard error were 8.1, 1,380, 16, and 1.8, respectively, for the 100-m AGL method, which were half the variability of the LPF and less than the 2-m AGL and visual estimate. For the purpose of measuring plant cover, all 3 new methods are as good as or better than visual estimation for speed, low standard deviation, and cost. The acquisition of a permanent image of a location is an important advantage of the 2- and 100-m AGL methods because vegetation can be reanalyzed using improved software or to answer different questions, and changes in vegetation over time can be more accurately determined. The reduction in cost per sample, the increased speed of sampling, and the lower standard deviation associated with the 100-m AGL digital imagery are compelling arguments for adopting this vegetation sampling method throughout western North American rangelands.