PREDICTING BIOMASS OF BEAVER FOOD FROM WILLOW STEM DIAMETERS

Beaver (Castor canadensis Kuhl) and willow (Salix spp,) are important components of riparian restoration on degraded western rangelands, Lan d managers need quantitative information to evaluate carrying capacity and potential habitat quality for beavers in riparian-willow systems, Our objectives were to determine the best model to predict biomass co mponents of coyote willow (S, exigua Nuttall) from basal stem diameter s and compare model predictions to diameter class averages, The study was conducted in a shrub-steppe ecosystem of northwestern Colorado, We estimated oven-dried weights of annual and total beaver food and tota l live biomass by diameter class from a sample of 160 willow stems. Se veral variants of a logistic function were fit with nonlinear least sq uares regression to select a model that best predicted mean biomass by stem diameter, A four-parameter logistic model provided the best fit for all 3 stem components. Predicted biomass estimates of beaver food and total live biomass had smaller standard errors than sample means f or all 10 stem diameter class midpoints, Percentage of stem weight tha t was beaver food varied from 93.6% for the smallest stems to 12.2% fo r the largest, We concluded that the logistic model provided reliable estimates of beaver food biomass and could be used with food consumpti on rates and stem density data to evaluate carrying capacity for beave r or test assumptions in the beaver habitat suitability index model.