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Transpiration and stomatal conductance across a steep climate gradient in the southern Rocky Mountains
Author(s) -
McDowell Nate G.,
White Sandra,
Pockman William T.
Publication year - 2008
Publication title -
ecohydrology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.982
H-Index - 54
eISSN - 1936-0592
pISSN - 1936-0584
DOI - 10.1002/eco.20
Subject(s) - transpiration , basal area , environmental science , elevation (ballistics) , allometry , hydrology (agriculture) , stomatal conductance , crown (dentistry) , atmospheric sciences , leaf area index , ecology , physical geography , geology , biology , geography , botany , photosynthesis , geometry , mathematics , geotechnical engineering , medicine , dentistry
Transpiration ( E ) is regulated over short time periods by stomatal conductance ( G s ) and over multi‐year periods by tree‐ and stand‐structural factors such as leaf area, height and density, with upper limits ultimately set by climate. We tested the hypothesis that tree structure, stand structure and G s together regulate E per ground area ( E g ) within climatic limits using three sites located across a steep climatic gradient: a low‐elevation Juniperus woodland, a mid‐elevation Pinus forest and a high‐elevation Picea forest. We measured leaf area : sapwood area ratio ( A l : A s ), height and ecosystem sapwood area : ground area ratio ( A s : A g ) to assess long‐term structural adjustments, tree‐ring carbon isotope ratios (δ 13 C) to assess seasonal gas exchange, and whole‐tree E and G s to assess short‐term regulation. We used a hydraulic model based on Darcy's law to interpret the interactive regulation of G s and E g . Common allometric dependencies were found only in the relationship of sapwood area to diameter for pine and spruce; there were strong site differences for allometric relationships of sapwood area to basal area, A l : A s and A s : A g . On a sapwood area basis, E decreased with increasing elevation, but this pattern was reversed when E was scaled to the crown using A l : A s . E g was controlled largely by A s : A g , and both E g and G s declined from high‐ to low‐elevation sites. Observation‐model comparisons of E g , G s and δ 13 C were strongest using the hydraulic model parameterized with precipitation, vapour pressure deficit, A l : A s , height, and A s : A g , supporting the concept that climate, G s , tree‐ and stand‐structure interact to regulate E g . Copyright © 2008 John Wiley & Sons, Ltd.