Comparison of some methods for collecting and analyzing data on aboveground net production and diversity of herbaceous vegetation in a northern Utah subalpine context

Abstract

Our major objective was to compare methods of collecting and analyzing data on herbaceous aboveground net primary production and plant diversity in sequence of sites inferred to represent a meadow → aspen → fir → spruce-sere in the middle Rocky Mountains. These comparisons should help us better interpret the literature and prepare for monitoring vegetation trends due to global climatic changes. Both absolute and relative values for above net primary production were highly dependent on methods used. The magnitude of differences in community diversity also varied greatly depending on the methods used to express plant richness, equitability, heterogeneity and dominance. We conclude that it is impossible to objectively test differences in production and diversity using data from single sampling dates and arbitrary choices of methods. In communities with great inter and intra-seasonal dynamics, an index of dominance that only measures magnitude (e.g. peak standing crop) was shown to have undesirable properties. We have demonstrated how average seasonal phytomass can overcome these problems by employing a measure of residence time as well as magnitude.