Crown Recession Patterns in Three Conifer Species of the Northern Rocky Mountains

Abstract

Abstract Crown length is a fundamental tree dimension for characterizing growth potential, wildlife habitat, and wood quality. The relative rates of height growth and crown recession determine the progression of crown length over time. We investigated patterns in crown recession of three co-occurring species in the northern Rocky Mountains: western white pine (Pinus monticola Dougl. ex D. Don), ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.), and interior Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco var. glauca). Past height, diameter, and crown base on 169 forest-grown trees were reconstructed by detailed stem analysis. Crown base was estimated for each year of the tree's life by dating the mortality of all whorl branches. Five-year crown recession was modeled in two parts, the first predicting the probability that a crown recedes and the second estimating recession conditional on its occurrence. The probability of crown recession increased and then decreased with an increasing crown ratio for all three species and similarly peaked over initial tree size. Conditional crown recession increased monotonically with crown ratio for ponderosa pine but peaked at crown ratios between 0.7 and 0.9 in western white pine and Douglas-fir. The resulting models lend insight into factors controlling rates of crown recession and their variation among species and differing initial conditions.