Available at: https://digitalcommons.calpoly.edu/theses/1753
Date of Award
MS in Forestry Sciences
Natural Resources Management
Montane meadows play a key role in the physical and biologic processes of coniferous forests in the western United States. However, due to climate change, over grazing, and fire suppression, conifer encroachment into meadows has accelerated. In some western regions, nearly half of all meadow habitat has been loss due to conifer encroachment. To combat this issue, encroaching conifers can be removed in an attempt to increase meadow habitat and function. While multiple studies have assessed changes in soil structure and vegetation composition, few studies directly investigate changes in hydrology following meadow conifer removal projects. The goal of this study is to determine if the removal of conifers from an encroached meadow (Marian Meadow) has an effect on soil moisture and groundwater depth such that meadow hydrologic conditions are promoted. This goal will be accomplished by the following objectives: 1) develop a water budget incorporating groundwater depth, soil moisture, and climate measurements to quantify the hydrologic processes prior to and after conifer removal, 2) conduct a statistical analysis of the project meadow’s wet season water table depth prior to and after conifer removal, 3) conduct a statistical analysis of the meadow’s soil moisture prior to and after conifer removal. Marian Meadow is located in Plumas County, CA at an elevation of 4,900 feet. This 45-acre meadow enhancement project is part of a 2,046-acre timber harvest plan implemented by the Collins Pine Company. Soil moisture and water table depth sensors were installed in Marian Meadow and a control meadow in September 2013. The soil moisture sensors were installed at one and three foot depths. Soil moisture and water table depth measurements used in this study span from September 2013 through June 2016. The removal of encroaching conifers from Marian Meadow occurred in July 2015. Evapotranspiration was estimated using the Priestly Taylor equation. Electrical Resistivity Tomography (ERT) was used to determine maximum water table depths. A groundwater recession curve equation was used to model water table depths between water table depth sensor measurements and ERT measurements. Standard least squared linear regression and ANCOVA was used to determine any statistical significant difference in soil moisture and water table depths prior to and after conifer removal. The water balance indicated that the majority of Marian Meadow and the control meadow’s water storage can be attributed to precipitation and not upland sources. This hydrologic characteristic is common in dry meadows. The statistical analysis indicated that measured water table depths increased on average by 0.58 feet following conifer removal. Relative to the control meadow, soil moisture in Marian Meadow initially decreased following conifer removal. However, from November 2015 through June 2016 soil moisture increased. On average soil moisture increased by 4% following conifer removal. Also, growing season (April through September) water table depths indicated that meadow vegetation communities could be supported in Marian Meadow following conifer removal. The removal of conifers from an encroached meadow appears to promote soil moisture and water table depth conditions indicative of a meadow and meadow plant community types.