Effects of forest stand density reduction on nutrient transport at the Caspar Creek Watershed

The Caspar Creek Experimental Watershed, located in the Jackson Demonstration State Forest, has been continuously studied since its establishment in 1962 as a collaboration between the California Department of Forestry and Fire Protection (CAL FIRE) and the U.S. Forest Service Pacific Southwest Research Station (PSW). The Caspar Creek Experimental Watershed has conducted thus far, two long-term research experiments. The primary goal of the first two experiments (1962-85, 1985-present) was to understand the effect of timber harvest on streamflow and suspended sediment concentrations in coastal-forested watersheds. The first experiment was set up as a classic paired watershed study. Cumulative effects (e.g. sediment, discharge) of removing 60-70% of the timber stand volume were studied in South Fork Caspar Creek and compared to the North Fork Caspar Creek watershed, which served as control. In the second experiment (1985-present) modern California Forest Practice Rules (FPRs) were tested in different sub-watersheds of the North Fork Caspar Creek and effects were compared among the different sub-watersheds.

In 2016, the PSW’s postdoctoral Research Hydrologist Dr. Salli Dymond designed a third experiment with the goal to expand upon the findings of the first two experiments to investigate the effect that different reductions in stand density (e.g. reduction in the quantity of trees) might have on the interconnected hydrological, geomorphic, and ecological processes in coastal redwood forests (Dymond 2016). To improve this understanding several research projects were set up that study these processes at the tree, plot, hillslope, sub-catchment and catchment scale. Table 1 shows the proposed stand reductions in the sub-watersheds of South Fork Caspar Creek. Most of the research is focused on four sub-watersheds, which will be harvested beginning in June 2018. The WIL watershed will serve as a control (0% vegetation removal), the TRE watershed will demonstrate a light harvest (35% reduction in stand density), the UQL watershed is a moderate harvest (55% reduction) and the ZIE watershed represents a high harvest (75% reduction).