Water Relations and Succession in Subalpine Conifers in Southeastern Wyoming

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Abstract
The water relations of 3 successional conifers, Pinus contorta Dougl. var. latifolia Engelm., Picea engelmanni Parry and Abies lasiocarpa (Hook.) Nutt., were monitored at early successional (open) and late successional (understory) sites through the summer of 1980 in southeastern Wyoming. Maximum leaf conductance to water vapor diffusion (gwv) at the open site was greatest in A. lasiocarpa, intermediate in P. contorta and least in P. engelmanni. Although values of maximum gwv were lower in all 3 conifers at the understory site than at the open site, the decrease was much greater for P. contorta vs. A. lasiocarpa and P. engelmanni. Minimum xylem pressure potentials were usually greater in P. contorta than in A. lasiocarpa and P. engelmannii at both sites. Reduction in the water vapor concentration difference between the leaf and air increased maximum gwv considerably in P. engelmanni and to a lesser extent in P. contorta and A. lasiocarpa. Maximum transpiration flux density was greatest in A. lasiocarpa, followed by P. contorta and P. engelmanni throughout most of the summer, with consistently greater values recorded at the open site. Differences in water relations among the 3 conifers may contribute to the observed early successional status of P. contorta compared with the late successional conifers (P. engelmanni and A. lasiocarpa) in the subalpine zone of the Rocky Mountains.

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