Comparison of regression methods for predicting singleleaf pinyon phytomass

Succession, nutrient cycling, production, and competition studies in plant communities require estimation of plant biomass. This is often accomplished by relating weight to easily measured plant dimensions via allometric equations. Dimensions of basal area and crown volume were used to predict phytomass of singleleaf pinyon (Finns monophylla Torr. & Frem.). Two regression methods for fitting the allometric equation to data for phytomass prediction were tested. These methods were the more commonly used logarithmic transformation of both data variables followed by linear regression analysis and an iterative nonlinear analysis without data transformation. The first was consistently less effective for predicting both individual tree and total plot phytomass for pinyon. Basal area was a better predictor of phytomass on a site than was crown volume. Prediction equations were highly site specific. Age of the trees in the stand used to derive the equations significantly affected the phytomass estimates. Other site and stand factors also appear to affect the phytomass-allometric parameter relationship.