Objectives of this study conducted in a western juniper (Juniperus occidentalis) dominated system of central Oregon were to: (1) evaluate tree canopy cover effects on effective precipitation and soil moisture recharge; and (2) assess surface water and groundwater connections in treated (juniper removed) and untreated watersheds. Detailed measurements of precipitation, tree canopy cover, and soil moisture were used to evaluate juniper interception and seasonal soil moisture fluctuations. Ephemeral stream runoff, springflow, and groundwater level data were used to characterize transient hydrologic connections within and out of the two watersheds. Results show that tree canopy cover was 29% at a watershed bottom location and 26% at an upstream hillslope location. On average, canopy interception was 44% at the bottom location and 36% at the hillslope location. In general, lower soil moisture values were obtained in the under-canopy locations when compared to the inter-canopy. Study findings indicate there are seasonal upland-valley hydrologic connections driven by a combination of winter precipitation and local geology that favors transient groundwater storage in the shallow aquifer. For the four-year period evaluated (2014-2017), greater groundwater level values were observed in all monitoring locations during the last two years where greater snowpack levels were measured. Snowpack and runoff relationships that were evaluated for years 2016 and 2017 show there were greater springflow levels in the treated watershed when compared to the untreated. An upward positive trend in springflow rates has been observed in the treated watershed following juniper removal in 2005. The untreated watershed has shown a flat trend response over the last 12 years. Results from this study contribute to improved natural resources management through a better understanding of the hydrologic connections occurring in rangeland ecosystems and the role that Western juniper encroachment may have on altering the hydrology of the site.
Oral presentation and poster titles, abstracts, and authors from the Society for Range Management (SRM) Annual Meetings and Tradeshows, from 2013 forward.