title: Hydraulic redistribution of soil water in two old-growth coniferous forests: quantifying patterns and controls.
abstract: Although hydraulic redistribution of soil water (HR) by roots is a widespread phenomenon, the processes governing spatial and temporal patterns of HR are not well understood. We incorporated soil/plant biophysical properties into a simple model based on Darcy's law to predict seasonal trajectories of HR. We investigated the spatial and temporal variability of HR across multiple years in two old-growth coniferous forest ecosystems with contrasting species and moisture regimes by measurement of soil water content (theta) and water potential (Psi) throughout the upper soil profile, root distribution and conductivity, and relevant climate variables. Large HR variability within sites (0-0.5 mm d(-1)) was attributed to spatial patterns of roots, soil moisture and depletion. HR accounted for 3-9% of estimated total site water depletion seasonally, peaking at 0.16 mm d(-1) (ponderosa pine; Pinus ponderosa) or 0.30 mm d(-1) (Douglas-fir; Pseudotsuga menziesii), then declining as modeled pathway conductance dropped with increasing root cavitation. While HR can vary tremendously within a site, among years and among ecosystems, this variability can be explained by natural variability in Psi gradients and seasonal courses of root conductivity.
authors.affiliation: USDA Forest Service, PNW Research Station, Corvallis, OR 97331.
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Warren
authors.affiliation: USDA Forest Service, PNW Research Station, Corvallis, OR 97331.
authors.forename: Frederick C
authors.initials: FC
authors.lastname: Meinzer
authors.affiliation: Western Ecology Division, US EPA/NHEERL, Corvallis, OR 97333.
authors.forename: J Renée
authors.initials: JR
authors.lastname: Brooks
authors.affiliation: Department of Wood Science and Engineering, Oregon State University, Corvallis, OR 97331.
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Domec
authors.affiliation: Dynamac Corporation, 200 SW 35th St, Corvallis, OR 97333, USA.
authors.forename: Rob
authors.initials: R
authors.lastname: Coulombe
mesh_terms: D002980:Climate; D017753:Ecosystem; D009922:Oregon; D018517:Plant Roots / Q000378:metabolism; D018526:Plant Transpiration; D012621:Seasons; D012987:Soil; D014197:Trees; D014861:Washington; D014867:Water
chemical_list: D012987:Soil; D014867:Water