Effect of increased rainfall on water dynamics of larch (Larix cajanderi) forest in permafrost regions, Russia: an irrigation experiment

Abstract

Sap flow measurements, from July to August 2004, were coupled with micrometeorological, soil moisture, and soil temperature measurements to analyze forest water dynamics in irrigated and undisturbed (control) larch (Larix cajanderi) forest plots in eastern Siberia. Plots were irrigated with 120 mm (20 mm day−1) of water from 17 to 22 July. Sap flow measurements of ten trees at each plot were scaled up to daily stand canopy transpiration (Ec). Canopy transpiration at the irrigation and control plots was similar before irrigation. Forest evapotranspiration (Ea) was obtained from Ohta et al. (Agric For Meteorol 148:1941–1953, 2008) while Ea in the irrigation plot was estimated based on the Ec_irrig/Ec_cont ratio. Rainfall during July–August was 63.4 mm but, after including water from thawing soil layers, the actual water input was 109.9 and 218.5 mm in the control and irrigation plots, respectively. Despite this large difference, a corresponding difference in Ec (and Ea) was not observed [42.6 (61.5) mm and 46.4 (71.8) mm in control and irrigation plots, respectively]. Daily canopy conductance (gc) increased as long as moisture was well supplied in the upper soil layers and evaporative demand was high. Soil moisture and rainfall contribution to Ea was 36.9 and 24.6 mm in the control plot and 34.5 and 37.3 mm in the irrigation plot, respectively. Water supply from soil thawing layers in the control plot and high runoff (105.6 mm) rates in the irrigation plot accounted for the similarity in water dynamics. Under increased precipitation, the forest used less soil water stored from previous growing seasons.