Deciduous Shrub Stem Water Content in Arctic Alaska
2022
Clark, Jason A. | Tape, Ken D. | Young-Robertson, Jessica M.
Vegetation water content is a critical aspect of ecosystem water balance and plant physiology, including how plants cope with drought. Deciduous trees store significant water for use in transpiration throughout the growing season in the boreal forest of Alaska. Water content of shrub stems, and their role in the water balance, remains unquantified for many woody species in boreal and arctic tundra ecosystems. We adapted time-domain reflectometry (TDR) to continuously measure shrub water content. We created calibration equations relating apparent dielectric constant to volumetric water content of shrub stems of felt-leaf willow (Salix alaxensis), diamond-leaf willow (S. pulchra) and dwarf birch (Betula nana). Our results show seasonal patterns of volumetric stem water content ranging from 40 to 70%. Stem water content prior to leaf-out was minimal (scaled by biomass, <2mm) compared to total snowmelt water, implying little water uptake of snowmelt water. Stem water content was small compared to other components of the hydrologic water budget (precipitation, runoff, evaporation, evapotranspiration, infiltration), indicating the importance of shrub transpiration and dependence of shrubs on available soil moisture for uptake. The technique and findings here are needed to quantify the role of deciduous shrub vegetation in the hydrologic cycle of ecosystems, particularly those where shrubs predominate.
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