Lower Elevational Limits of Montane Trees. II. Environment-Keyed Responses of Three Conifer Species

Abstract

Growth experiments were performed in the laboratory and in the field with plants of Pinus attenuata Lemm., knobcone pine; P. coulteri D. Don, Coulter pine; and P. lambertiana Dougl., sugar pine. Comparative responses were interpreted in the light of native lower elevational limits; in the study area, knobcone is found at lowest elevations, Coulter at middle elevations, and sugar at highest elevations. Pinus attenuata and P. coulteri appear to be much alike, with P. lambertiana distinctly different in several respects. These include: phenology of shoot and needle elongation, drought tolerance of seedlings, survival of seedlings in the field, rooting pattern in the field, sensitivity of diameter growth rate to low elevation. The latter two phenomena were discussed in a previous paper in which it was suggested that lower limits of Coulter and knobcone would more nearly coincide if it had not been for the effects of repeated wildfires. This suggestion is substantiated by the work reported here.