Hydraulic Architecture and Structure of Abies lasiocarpa Seedlings in Three Subalpine Meadows of Different Moisture Status in the Eastern Olympic Mountains, Washington, U.S.A.

Abstract

Hydraulic function and structural characterististics were measured during summer drought in 30 subalpine fir seedlings growing in three meadows of different moisture status close to the tree line in the eastern Olympic Mountains, Washington, U.S.A. No significant between-site differences were detected in the specific stem conductivities (hydraulic conductivity per transverse sapwood area) of the seedlings. The portion of needle mass to total aboveground mass decreased with decreasing moisture status. Leaf-specific conductivities (LSCs—hydraulic conductivity per dry weight of supplied needles) and Huber values (transverse sapwood area per dry weight of supplied needles) increased with decreasing site moisture status. These patterns indicate that the needle surface area supplied by a unit of stem transverse sectional sapwood area declined with site moisture status. Because the stem hydraulic conductivity was unaffected by site moisture status, it was inferred that embolism had probably not occurred in the drier site. We suggest that the absence of subalpine fir on very dry sites may be mainly due to an inadequate carbon balance; less foliage area would support a relatively large stem cross-sectional area.