Predicting Shrub Biomass and Current Annual Growth from Field Measurements in the Oregon Coast Range

Abstract

Estimates of plant biomass derived from field measurements can be used to quantify wildlife habitat, fuel loads, net primary production, and nutrient cycling. The difficulty involved with developing species-specific allometric equations for plant biomass results in many studies utilizing estimates of shrub cover instead. We assess whether reasonable predictive equations for shrub biomass can be achieved across a group of six common shrub species growing on recent clearcuts in the Oregon Coast Range. Variables used in the models were total basal area summed across stems, height, and crown area (plan view) using an ellipse formula based on crown length and width measurements. Species-level models had adjusted R2 values ranging from 0.76–0.99 for total biomass and current growth. An all-species model had an adjusted R2 of 0.93 for total biomass and 0.84 for current growth. The aggregate models applied to the individual species gave similar R2 values except for current annual growth of oceanspray (Holodiscus discolor) and vine maple (Acer circinatum). Simpler models based just on crown area or crown area plus height ranged from adjusted R2 of 0.63–0.68 for all-species models of total or current biomass. These deciduous shrub biomass models can be used to help estimate forage and cover for birds, ungulates, and other wildlife. Furthermore, these models might prove useful for other plant species growing under similar geographic and climatic conditions; however, caution is warranted as the models should be validated with some destructive plant sampling for other species or use in other regions.