Journal Article

Restoration thinning and influence of tree size and leaf area to sapwood area ratio on water relations of <i>Pinus ponderosa</i>

K. Simonin, T. E. Kolb, M. Montes-Helu and G. W. Koch

in Tree Physiology

Volume 26, issue 4, pages 493-503
Published in print April 2006 | ISSN: 0829-318X
Published online April 2006 | e-ISSN: 1758-4469 | DOI: http://dx.doi.org/10.1093/treephys/26.4.493
Restoration thinning and influence of tree size and leaf area to sapwood area ratio on water relations of Pinus ponderosa

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Ponderosa pine (Pinus ponderosa Dougl. ex P. Laws) forest stand density has increased significantly over the last century (Covington et al. 1997). To understand the effect of increased intraspecific competition, tree size (height and diameter at breast height (DBH)) and leaf area to sapwood area ratio (AL:AS) on water relations, we compared hydraulic conductance from soil to leaf (kl) and transpiration per unit leaf area (QL) of ponderosa pine trees in an unthinned plot to trees in a thinned plot in the first and second years after thinning in a dense Arizona forest. We calculated kl and QL based on whole- tree sap flux measured with heat dissipation sensors. Thinning increased tree predawn water potential within two weeks of treatment. Effects of thinning on kl and QL depended on DBH, AL:AS and drought severity. During severe drought in the first growing season after thinning, kl and QL of trees with low AL:AS (160–250 mm DBH; 9–11 m height) were lower in the thinned plot than the unthinned plot, suggesting a reduction in stomatal conductance (gs) or reduced sapwood specific conductivity (KS), or both, in response to thinning. In contrast kl and QL were similar in the thinned plot and unthinned plot for trees with high AL:AS (260–360 mm DBH; 13–16 m height). During non-drought periods, kl and QL were greater in the thinned plot than in the unthinned plot for all but the largest trees. Contrary to previous studies of ponderosa pine, AL:AS was positively correlated with tree height and DBH. Furthermore, kl and QL showed a weak negative correlation with tree height and a strong negative correlation with AS and thus AL:AS in both the thinned and unthinned plots, suggesting that trees with high AL:AS had lower gs. Our results highlight the important influence of stand competitive environment on tree-size-related variation in AL:AS and the roles of AL:AS and drought on whole-tree water relations in response to thinning.

Keywords: Arizona; carbon allocation; hydraulic conductance; intraspecific competition; transpiration

Journal Article.  0 words. 

Subjects: Plant Sciences and Forestry

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