Basal area and hillslope position impacts to hydraulic redistribution in a coast redwood forest

In forest ecosystems, the interplay among plant-driven processes and anthropogenic activities profoundly influences water balance dynamics. Hydraulic redistribution is one plant-driven process that can provide a large proportion of a plant's daily water. However, critical gaps exist in our knowledge of hydraulic redistribution including how forest management processes, like thinning, and site-specific factors like basal area and hillslope position, may affect it. To address these gaps, we used hourly volumetric water content measurements from 2016 to 2021 from four sub-watersheds in a coast redwood forest, three of which were harvested at different basal area reductions in 2018. This dataset enabled us to investigate the effects of thinning, variations in basal area, and hillslope position on hydraulic redistribution magnitude and additional days of soil moisture provided by hydraulic redistribution. We found that thinning had no significant effect on hydraulic redistribution magnitude or on the days of additional stored water provided. However, there were significant differences in soil moisture and hydraulic redistribution magnitude among the different basal area groups — low basal area had the highest magnitude of hydraulic redistribution. Similarly, soil moisture and hydraulic redistribution varied among hillslope positions and positions higher on the hillslope had higher magnitudes of hydraulic redistribution. Our findings suggest that a combination of climatic factors and site-specific characteristics may play a crucial role in determining soil moisture and hydraulic redistribution dynamics in coast redwood forests.