Review and assessment of various techniques for estimating net aerial primary production in grasslands from harvest data

Abstract

Methodology for calculating aboveground net production (ANP) has progressed from a single estimate of total standing crop at the end to an evaluation of multiple categories of biomass (viz. live, recent dead, old dead) by species and considering, with statistical constraints, each peak during the growing season. We have reviewed the published methods for calculating ANP with the purpose of critically comparing them with each other and with current understanding of primary productivity. As a further comparison of methods we have calculated net aboveground production by 13 methods on sets of harvest data collected by the US/IBP Grassland Biome. The data represent a grazed and ungrazed treatment on 10 sites of six grassland types. One to three years of data were available for each site. A hierarchical cluster analysis showed that all methods except one were significantly correlated (r ≤ 0.61). Analysis of variance indicated that although all methods were significantly correlated, there were significant differences among the methods in terms of usefulness as discriminators of sites, years, or treatments. For various utilitarian and theoretical reasons the numbers of methods were reduced to two groups of "best estimators." One group consisted of two methods involving summation of species peaks, the first utilizing live biomass, the second live + recent dead biomass. The second group comprised three methods using trough-peak analysis on live, live + recent dead, and live + recent dead + old dead biomass. Analysis for linear relations between the "best estimator" methods and 15 abiotic variables showed many significant relationships.