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Ecohydrologic connectivity in semiarid watersheds of central Oregon: A paired watershed study.

TitleEcohydrologic connectivity in semiarid watersheds of central Oregon: A paired watershed study.
Publication TypeConference Paper
Year of Publication2015
AuthorsRay, G, Ochoa, C, Deboodt, T, Fisher, M, Buckhouse, J, Borman, M
Conference NameSociety for Range Management - Annual Meeting
Date Published01/2015
Conference LocationSacramento, CA

There is an increasing concern by range managers for understanding the effects that western juniper (Juniperus occidentalis) has on the ecologic and hydrologic state of western rangelands. This paired watershed study considers hydrologic function while investigating the long-term effects of juniper removal on vegetation composition and soil water availability at the watershed scale. Juniper under 140 years of age were removed from one watershed in 2005 after 12 years of reconnaissance monitoring. Analysis of historical data revealed precipitation as a trigger for increasing soil water content at the deepest soil profile measured (80 cm). This soil response and subsequent shallow groundwater level rise observed in selected piezometers seemed to indicate a direct connectivity between precipitation, soil, vegetation and groundwater. These results were more evident in the treated when compared to the untreated watershed and led us to further our investigation of the understanding of the hydrologic connectivity between precipitation, vegetation, and soil water response. Objectives of this ongoing study are to 1) characterize the understory vegetation composition of a previously treated and untreated watershed, and 2) determine soil-water-vegetation relationships within a pair of previously treated and untreated watersheds. Near 300 monitoring transects were established to determine vegetation-soil texture-soil water content relationships in both watersheds. Multiple points were measured at each transect to determine vegetation composition and cover, to characterize soil textural properties, and to assess soil water content distribution. Preliminary results suggest similarities in soil volumetric water content and vegetation composition when compared to aspect in both watersheds. In the treated watershed, average soil volumetric water content was 8% and vegetation cover was 80%. Preliminary results from the soil texture analysis reveal a high composition of sandy loam and other lighter textured soils. These findings may have implications for the better understanding of plant-water-soil interactions in western juniper woodlands, and a further investigation into results will hope to strengthen the linkage between these interactive systems.