Mount Pinos at the western margin of the Transverse Ranges of Southern California. reaches 2692 m in elevation at its peak. The broad summit of the mountain supports an area of subalpine fellfield vegetation, as well as an unusual low elevation occurrence of limber pine (Pinus flexilis). We describe the summit area of the mountain and characterize the community structure and ecophysiology of the fellfield community and associated pines. The fellfield community, dominated by low mats and cushions of Eriogonum kennedyi, Phlox diffusa, and Lupinus breweri var. bryoides, has a mean plant cover of 44%. These fellfield species have amphistomatic leaves with abundant, slender palisade cells on both sides of the mesophyll. These traits represent a strategy shared with desert plants. Amphistomaty helps to increase assimilation by maximizing stomatal conductance to CO2 during the gas phase of diffusion, and the isolateral mesophyll maximizes diffusion of CO2 by exposing a very high mesophyll membrane area per leaf surface area. However, the mean maximum rates of assimilation measured for Phlox diffusa, Eriogonum kennedyi, Astragalus purshhii var. tinctus, and Lupinus breweri var. bryoides were 6.8 to 13.9 µmol CO2 m−2 s−1, placing them in the lower range of those measured in alpine areas of the world.
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Vol. 55 • No. 1