Equations for estimating biomass and leaf area of plants in the Pacific Northwest

Abstract

Reliable estimates of plant biomass and leaf surface area are essential for studying primary production, nutrient cycling, hydrology, wildlife management, and fire. This paper presents equations that can be used to make such estimates for most plant species-trees, shrubs, and herbs-dominant in western and central Oregon.' We also document the methods used for each equation (such as locations and sizes of sampled plants), summarize statistical attributes (sample sizes, variances, rz ), and reference previously published data. Most of the equations presented here are a product of the Coniferous Forest Biome, part of the United States' participation in the International Biological Program (IBP). The original studies focused on undisturbed oldgrowth forests (more than 450 years old) of Pseudotsuga menziesii. Followup studies still underway are evaluating the responses of those same systems to perturbations, especially clearcutting, and the importance of streamside vegetation. Therefore, most equations apply best to three basic habitats, all in the western Cascade Mountains of Oregon: mature coniferous forests, streamside (riparian) zones, and clearcuttings less than 10 years old. The vegetation and microclimates of these areas have been detailed by Dyrness (1973), Franklin and Dyrness (1973), Dryness et al. (1974), and Zobel et al. (1976). Sometimes we tried to make an equation represent a broader range of habitats. For example, Grier and Logan (1977) already used about half the data from our Pseudotsuga menziesii equations to derive others heavily weighted toward old-growth forests in the west-central Cascade Mountains of Oregon (Appendix B, Reference 4). Because we felt that a set of equations for predicting average plant biomass on diverse sites would be more useful than one tailored to a particular area or habitat, our Pseudotsuga menziesii equations are composites of five data sets collected throughout the Pacific Northwest. Note that our equations for Pinus ponderosa, Oplopanax horridum, and Pinus contorta used data from areas outside the Pacific Northwest.