Population variation in ecophysiological traits of four co-occurring montane conifers was measured on a large latitudinal gradient to quantitatively assess their potential for response to environmental change. White fir (Abies concolor) had the highest variability, gross photosynthetic rate (Pg), and foliar carbon (C) and nitrogen (N) content. Despite low water use efficiency (WUE), stomatal conductance (gs) of fir was the most responsive to unfavorable environmental conditions. Pinus lambertiana exhibited the least variability in Pg and WUE, and is likely to be the most vulnerable to environmental changes. Pinus ponderosa had an intermediate level of variability, and high needle growth at its higher elevational limits. Pinus Jeffreyi also had intermediate variability, but high needle growth at its southern latitudinal and lower elevational limits. The attributes used to assess tree vigor were effective in predicting population vulnerability to abiotic (drought) and biotic (herbivore) stresses. Variability in ecophysiological attributes of western U.S. conifers suggests relative capacity of species and populations to respond to environmental change.

Effects of canopy ozone (O3) exposure and signatures of genetic structure using isozyme markers associated with O3 tolerance were analyzed in 20-, 80-, and >200-yr-old ponderosa (Pinus ponderosa Dougl. ex Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.) in Sequoia National Park, California. For both species, the number of alleles and genotypes per loci was higher in parental trees relative to saplings. In ponderosa pine, the heterozygosity value increased, and the fixation index indicated reduction of homozygosity with increasing tree age class. The opposite tendencies were observed for Jeffrey pine. Utilizing canopy attributes known to be responsive to O3 exposure, ponderosa pine was more symptomatic than Jeffrey pine, and saplings were more symptomatic than old growth trees. We suggest that these trends are related to differing sensitivity of the two species to O3 exposure, and to higher O3 exposures and drought stress that younger trees may have experienced during germination and establishment. Genetic variation in isozyme markers associated with ozone tolerance differed between parental trees and their progeny in two closely related species of yellow pine.