THE TRADE-OFF BETWEEN SPECIES CAPTURE AND QUANTITATIVE ACCURACY IN ECOLOGICAL INVENTORY OF LICHENS AND BRYOPHYTES IN FORESTS IN MONTANA

For a given level of sampling effort there is a trade-off between accuracy of cover estimates and the proportion of the species present that are recorded in the data ("species capture"). We evaluated this trade-off for three strata of lichens and bryophytes in western Montana: branch epiphytes, trunk epiphytes, and ground layer. At one extreme, visually integrating a single large plot resulted in high species capture but low accuracy of cover estimates. At the other extreme, subsampling with many small plots, species capture was low but accuracy of cover estimates was higher for common species. Belt transects were intermediate in both respects. In general, larger areas of visual integration are preferable when the vegetation is sparse. Differences in sampling times between methods were mostly minor, and these differences were inconsistent among strata. When density and diversity of vegetation in a stratum are relatively high, sampling times are somewhat longer. To represent effectively both species diversity and cover, we recommend subsampling with small quadrats when vegetation is relatively dense or belt transects with sparse vegetation. These techniques should be supplemented by a fixed-area reconnaissance for species not included in the quantitative sample.