ETD RECORD
Transpiration and canopy conductance of mixed species conifer stands in an inland Pacific Northwest forest
Citation
Pangle, Robert Earl.. (2008). Transpiration and canopy conductance of mixed species conifer stands in an inland Pacific Northwest forest. Theses and Dissertations Collection, University of Idaho Library Digital Collections. https://www.lib.uidaho.edu/digital/etd/items/etd_344.html
- Title:
- Transpiration and canopy conductance of mixed species conifer stands in an inland Pacific Northwest forest
- Author:
- Pangle, Robert Earl.
- Date:
- 2008
- Keywords:
- Forest canopy ecology--Idaho Plants--Idaho--Transpiration
- Program:
- Natural Resources
- Abstract:
- During 2004 and 2005, we examined the influence of increasing tree height on canopy level stomatal conductance and transpiration in five tree species growing in mixed coniferous forests located in northern Idaho, USA. In a replicated study involving nine stands of varying height, we measured stem sap-flux rates in 50 trees that ranged in height from 4.8 to 42.7 m. Across the 2-year sampling period, we observed significant decreases in leaf-level canopy conductance (GS) with increasing tree height for the Larix occidentalis, Pinus monticola, and Tsuga heterophylla trees in our study. We also observed decreases in canopy conductance (GS) with increasing height in Thuja plicata, but the rate of decline was not statistically significant. We did not observe a decline in canopy GS across the 2-year sampling period in the Pseudotsuga menziesii var. glauca trees that we measured. Specifically, across all species and years, daily mean GS averaged 28.9 (3.0), 21.9 (1.9), and 19.1 (1.5) mmol m{esc}p-2{esc}ss{esc}p-1{esc}s respectively for the short, intermediate, and tall height class trees in our study. Our observations of declining GS with increasing tree height are in agreement with a central tenet of the hydraulic limits hypothesis, which predicts decreased leaf level stomatal conductance as hydraulic resistance in the xylem pathway increases with tree height.;In a second portion of the study, we estimated stand-level water flux and canopy gas exchange rates using sap-flux measurements of tree water flux (JS) scaled to the canopy level. Across the 2-year sampling period, mean daily stand transpiration (EC) averaged 1.25 (0.35), 1.57 (0.10), and 1.45 (0.32) mm day{esc}p-1{esc}s respectively for short, intermediate, and tall height class stands. We observed no significant decrease in average stand level canopy transpiration as stand height increased. Daily mean canopy conductance (GC) across the 2-year study averaged 3.31 (0.87), 3.29 (0.12), and 3.07 (0.47) mm s{esc}p-1{esc}s respectively for the short, intermediate, and tall height class stands. Similar to stand EC, we did not observe a significant decline in average stand level canopy conductance (GC) as stand height increased. However, there was a site specific trend of decreasing GC with canopy height increase, and this trend was observed to be even stronger when a short class stand with low stem density and low LAI was removed from the analysis. Total stand sapwood area and LAI varied considerably across the stands in our study, and along with changes in species composition, these variables had a strong impact on estimates of stand EC and GC. In conclusion, we observed significant decreases in leaf-level transpiration and stomatal conductance with increasing tree height. However, these decreases at the leaf level were not always observed when sap-flux rates were scaled to the ground and canopy level due to site specific variations in species composition, total stand sapwood area, and LAI.
- Description:
- Thesis (Ph. D., Natural Resources)--University of Idaho, October 2008.
- Major Professor:
- Kathleen L. Kavanagh.
- Defense Date:
- October 2008.
- Type:
- Text
- Format Original:
- xxi, 177 leaves :ill. ;29 cm.
- Format:
- record
Rights
- Rights:
- In Copyright - Educational Use Permitted. For more information, please contact University of Idaho Library Special Collections and Archives Department at libspec@uidaho.edu.
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