Table 1_Hydrological response to thinning in forest stands: analysis of soil volumetric water content and soil water flux.docx

Thinning practices have increased to maintain healthy and resilient forests. However, there is a growing concern about the potential effects of thinning on hydrological response. We analyzed the influence of thinning on shallow soil water flux in a mixed conifer forest by comparing paired treated and control plots. Sensors measured soil volumetric water content and soil matric potential at different depths to compute soil water fluxes over five seasons. Additionally, we analyzed soil temperature and soil volumetric water content data. Thinning treatment led to upward soil water flux during the study period (2009–2011), regardless of the season. This was mainly due to differences in soil gradients, possibly associated with an increased soil temperature by as much as 2.65 °C due to increased solar radiation. Although thinning increased upward water flux (< 0.2 mm day−1), it constituted a negligible part of the soil volumetric water content stored in thinned plots, which was 0.15 cm3 cm−3 greater, at 35 cm depth, than in control plots. Our findings suggest that thinning can contribute to soil moisture storage even during dry periods, likely stored at the bottom of the soil column on a rock surface. Thinning can have a positive impact on the resilience of forests to droughts and other climate-related stresses.