THE ECOLOGY OF ELEVATIONAL POSITIONS IN PLANTS - DROUGHT RESISTANCE IN 5 MONTANE PINE SPECIES IN SOUTHEASTERN ARIZONA

We subjected seedlings of five pine species from the Chiricahua Mountains, Arizona to drought in the greenhouse to assess the relationships among elevational position, drought resistance, and biomass allocation. In comparison with upper elevation species, lower elevation species survived longer and experienced less depression of photosynthesis in response to the imposed drought. During the last week of the 29-d drought, internal water potential decreased little in lower elevation species but dropped precipitously in upper elevation species. Thus, relative drought resistance and elevational position of these pines seem associated with the ability of seedlings to survive drought by maintaining favorable plant water potential. Lower elevation and more drought-resistant species allocated less biomass to roots than did other species, a fact suggesting, contrary to assumptions of recent plant community models, that biomass allocation was unimportant in species differences in drought resistance.