© 2003 Heron Publishing—Victoria, Canada
Reliance on stored water increases with tree size in three species in the Pacific Northwest
N. G. Phillips (1, 2), M. G. Ryan (3, 4), B. J. Bond (5), N. G. McDowell (5), T. M. Hinckley (6) and J. Cermák (7)
1. Geography Department, Boston University, Boston, MA 02215, USA / 2. Author to whom correspondence should be addressed (Nathan@bu.edu) / 3. USDA Forest Service, Rocky Mountain Research Station, Fort Collins, CO 80526, USA / 4. Department of Forest Sciences and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA / 5. Forest Science Department, Oregon State University, Corvallis, OR 97331, USA / 6. College of Forest Resources, University of Washington, Seattle, WA 98195, USA / 7. Institute of Forest Ecology, Mendel University of Agriculture and Forestry, 62 100 Brno, Czech Republic / Received May 16, 2002; accepted August 30, 2002; published online February 3, 2003
Summary
In tall old forests, limitations to water transport may limit maximum tree height and reduce photosynthesis and carbon sequestration.
We evaluated the degree to which tall trees could potentially compensate for hydraulic limitations to water transport by increased
use of water stored in xylem. Using sap flux measurements in three tree species of the Pacific Northwest, we showed that reliance
on stored water increases with tree size and estimated that use of stored water increases photosynthesis. For Douglas-fir
(Pseudotsuga menziesii (Mirb.) Franco), water stored in xylem accounted for 20 to 25% of total daily water use in 60-m trees, whereas stored water
comprised 7% of daily water use in 15-m trees. For Oregon white oak (Quercus garryana Dougl. ex Hook.), water stored in xylem accounted for 10 to 23% of total daily water use in 25-m trees, whereas stored water
comprised 9 to 13% of daily water use in 10-m trees. For ponderosa pine (Pinus ponderosa Dougl. ex Laws.), water stored in xylem accounted for 4 to 20% of total daily water use in 36-m trees, whereas stored water
comprised 2 to 4% of daily water use in 12-m trees. In 60-m Douglas-fir trees, we estimated that use of stored water supported
18% more photosynthesis on a daily basis than would occur if no stored water were used, whereas 15-m Douglas-fir trees gained
10% greater daily photosynthesis from use of stored water. We conclude that water storage plays a significant role in the
water and carbon economy of tall trees and old forests.
Keywords:
hydraulic capacitance, Pinus ponderosa, Pseudotsuga menziesii, Quercus garryana, sapwood, water storage, xylem.
