Submitted to: John Wiley Journal
Publication Type: Book / Chapter
Publication Acceptance Date: February 17, 2005
Publication Date: July 1, 2005
Citation: Link, T.E., G.N. Flerchinger, M. Unsworth, and D. Marks. 2005. Water relations of old-growth Douglas fir stands. In: C. De Jong, D. Collins, and R. Ranzi (eds.), Climate & Hydrology in Mountain Areas. John Wiley & Sons, Ltd., Chichester, England. Chap 11: pp.147-159. Interpretive Summary: In many areas of the world, growing populations depend on forested upland areas as a source of high quality water resources. Competing resource demands for timber production, municipal and irrigation water supplies, and survival of endangered species emphasize the need to understand how forest vegetation affects hydrological fluxes. Concern about the impacts of climate and land cover change on water resources and flood-generating processes emphasize the need for understanding the interactions between forest canopies, snowmelt and plant water use. Quantification of these fluxes for old-growth canopies provides a reference point for unmanaged, old forests, for comparison to younger age classes that currently comprise large tracts of forestlands. Detailed measurements and model simulations were conducted on an old growth forest at the Wind River Canopy Crane Research Facility located in southwestern Washington. Our results indicate that a relatively simple representation of the vegetation canopy can accurately simulate seasonal hydrologic fluxes in this environment, except during periods of discontinuous snowcover. This will allow us to investigate how snowmelt, plant water use, and water availability might be expected to change in this system as a result of climatic shifts.
Technical Abstract: Concern about the impacts of climate and land cover change on water resources and flood-generating processes emphasize the need for a mechanistic understanding of the interactions between forest canopies and hydrologic processes. Application of the Simultaneous Heat and Water Model to simulate hydrologic processes in an old-growth forest was demonstrated at the Wind River Canopy Crane Research Facility (WCCRF) in southwestern Washington. Results from the SHAW simulations exhibited good agreement with measured precipitation throughfall and soil moisture profiles and with estimates of transpiration and ET fluxes. We therefore feel that the model can be used to provide good estimates of the water balance dynamics of the WRCCRF site. Model results indicated that for the two study years, ET on average accounted for approximately 9 and 12% of the annual water balance, respectively. Evaporation of intercepted water during the rainfall season accounted for almost 25% of the water balance, probably due to relatively high canopy saturation storage resulting from the abundant canopy epiphyte populations. These results indicate that a relatively simple representation of the vegetation canopy can accurately simulate seasonal hydrologic fluxes in this environment, except during periods of discontinuous snowcover