HR: 08:20h
AN: B21D-02    [Abstracts]
TI: What Trees do at Night When no one is Looking: Impacts of Elevation on Hydraulic Redistribution in Mountainous Terrain
AU: * Kavanagh, K
EM: katyk@uidaho.edu
AF: University of Idaho, Department of Forest Resources, Moscow, ID 83844, United States
AU: Blecker, S W
EM: sblecker@uidaho.edu
AF: University of Idaho, Department of Forest Resources, Moscow, ID 83844, United States
AU: Pangle, R
EM: rpangle@vandals.uidaho.edu
AF: University of Idaho, Department of Forest Resources, Moscow, ID 83844, United States
AU: Gag, P
EM: gag3560@uidaho.edu
AF: University of Idaho, Department of Forest Resources, Moscow, ID 83844, United States
AB: Changes in climate and terrain variables (such as vapor pressure deficit (VPD), temperature, soil and moisture), that occur along elevational gradients can result in physiological differences in steep mountainous terrain. This is particularly evident in the plant mediated portion of the hydrologic cycle such as the redistribution of soil moisture by tree roots or hydraulic redistribution (HR). In forests of the intermountain Northwest, HR typically occurs when the following conditions are met: 1) A sufficient water potential gradient exists within the soil profile, and 2) Nighttime VPD is negligible, whereby the lack of transpiration allows water transported in the roots from deeper moist soil horizons to "leak" out in the upper dry soil layers rather than being transpired by the tree. We hypothesized that the formation of nocturnal cold air pools in steep terrain increases the frequency and magnitude of water transported by HR and decreases nocturnal transpiration in cold low elevation sites relative to the warmer upper elevation sites. We measured VPD, nocturnal transpiration and soil moisture profiles along elevational gradients in two steep forested ecosystems in Northern Idaho. At Mica Creek, nighttime VPD averaged 0.60 kPa, 1.16 kPa and 0.94 kPa at the lower (1210m), mid (1250m) and upper (1390m) site respectively. We have confirmed that the combination of open stomata and high nocturnal atmospheric VPDs results in nocturnal transpiration and will present elevational trends of nocturnal transpiration and HR. At Benton Creek, average minimum daily VPDs increased from 0.28 kPa to 0.54 kPa as elevation increased from 900m to 1150m. Evidence of HR tended to occur later in the summer and moved less water as elevation increased. Shifts in the magnitude and timing of HR with elevation have potential hydrologic and ecologic ramifications. During the typical extended periods of summer drought in these ecosystems, HR may help to provide moisture to neighboring shallow rooted vegetation, maintain fine root viability and rhizosphere activity and allow for continued mineralization and access to nutrient stores in the upper soil layers.
DE: 0438 Diel, seasonal, and annual cycles (4227)
DE: 0495 Water/energy interactions (1878)
DE: 1813 Eco-hydrology
DE: 1818 Evapotranspiration
DE: 1852 Plant uptake
SC: Biogeosciences [B]
MN: 2007 Fall Meeting