Thu, Aug 05, 2021:On Demand
Background/Question/Methods
Fog inundation along California’s coastal mountain range creates microclimates that support coast redwood (Sequoia sempervirens, D. Don) forests during the summer drought period. Fog serves as a vital ecosystem connector by reducing transpiration rates and serving as a direct water source. Previous studies show that fog presence and its ecological effects vary based on local topography, climate conditions, and forest structure. This study contributes to our understanding of fog distribution and impacts following forest harvesting in the coast redwood forest. Fog presence and ecosystem responses (e.g., climate, soil moisture, sap flow) were monitored at the Caspar Creek Experimental Watersheds in northwestern California over the 2020 fog season (Jun – Sept). Observations were recorded at shoulder and ridge topographic positions in harvested and unharvested 3rd-growth forest. We examined the 1) temporal and spatial distribution of fog, 2) soil moisture responses to fog events, and 3) the influence of fog on transpiration. Leaf wetness sensors were used to detect fog presence in the canopy and water inputs to the litter layer. Soil moisture sensors were located at three positions varying in distance from the canopy of the transpiration study trees.
Results/Conclusions Fog presence was found to vary across the landscape with no significant relationship to harvesting type but differed based on topographic position. Fog intensity was higher at the shoulder position than at the ridge of the hillslope. Small increases in soil and litter moisture were observed at all four study sites in response to fog events despite high temporal variation through the season. Surficial soil moisture was highest near the boles of the S. sempervirens trees at the shoulder hillslope positions, regardless of harvest condition. All sites displayed lower transpiration rates during fog periods, but the greatest reduction was at the unharvested sites. In summary, presence and intensity of fog was variable through the season and, when present, led to lower VPD and transpiration rates. Overall, our research suggests that the distribution of fog and its ecological effects at the Caspar Creek Experimental Watersheds is primarily driven by site-specific characteristics such as topography and species composition rather than forest density.
Results/Conclusions Fog presence was found to vary across the landscape with no significant relationship to harvesting type but differed based on topographic position. Fog intensity was higher at the shoulder position than at the ridge of the hillslope. Small increases in soil and litter moisture were observed at all four study sites in response to fog events despite high temporal variation through the season. Surficial soil moisture was highest near the boles of the S. sempervirens trees at the shoulder hillslope positions, regardless of harvest condition. All sites displayed lower transpiration rates during fog periods, but the greatest reduction was at the unharvested sites. In summary, presence and intensity of fog was variable through the season and, when present, led to lower VPD and transpiration rates. Overall, our research suggests that the distribution of fog and its ecological effects at the Caspar Creek Experimental Watersheds is primarily driven by site-specific characteristics such as topography and species composition rather than forest density.