Predicting Age of Pinyon and Juniper Using Allometric Relationships

Management of pinyon-juniper ecosystems often is hampered by insufficient tree age structure data. We developed allometric relationships based on visible and easily measured tree characteristics as tools for predicting tree age. In this study, we tested tree height, diameter at root collar, and crown radius using both single- and multiple-regression analyses to determine which attributes best correlated with tree age. Because soil type and site productivity often affect growth rates of pinyon and juniper, three common soil types in northern Arizona were assessed to determine variation in regression equations. Stepwise regression analysis determined that height and diameter at root collar of juniper were the best variables for predicting age. For pinyon, crown radius on basalt-derived soil and diameter at root collar on limestone-derived soil were the variables of best fit; however, we suggest using diameter at root collar across all sites. We developed models from these allometric relationships to aid in the management of the pinyon-juniper ecosystem.