Location: Northwest Watershed Research CenterTitle: Shrubland ecohydrologic response and recovery over a ten year period following pinyon and juniper removal
Submitted to: Fire Ecology
Publication Type: Abstract Only
Publication Acceptance Date: 9/2/2016
Publication Date: N/A
Technical Abstract: Pinyon and juniper range expansion has altered plant community structure, hydrologic function, ecological condition, and the delivery of ecosystem goods and services on millions of hectares in the western US. On many rangeland sites, encroaching pinyon and juniper trees out-compete shrubs and herbaceous vegetation for limited water and nutrients and thereby facilitate a decline in vigor and cover of understory plants. These cover declines commonly promote increased bare ground, high runoff rates, and long-term surface soil loss. Numerous ecosystem services decline with site degradation over time. Occurrence of large, high severity fires is also increasing on western rangelands encroached by pinyon and juniper species. Conifer encroachment increases the woody fuel loading necessary for such fires. Land managers throughout the western US are in need of scientific-based information to guide management actions on woodland encroached rangelands, including shrubland restoration and fuels reduction. This study investigated the impacts of pinyon and juniper encroachment and tree removal on vegetation, hydrology, and erosion on sagebrush rangelands. A suite of rainfall simulation and concentrated overland flow experiments were employed to measure infiltration, runoff, and erosion processes prior to tree removal and 1, 2, and 10 years after tree removal. Vegetation and soils were characterized at multiple spatial scales in each year of the study. Prior to tree removal, extensive bare ground under tree-dominated conditions facilitated high rates of runoff and erosion. Distributing masticated or shredded tree debris into bare areas increased infiltration and reduced erosion in the first few years following tree mastication. Cutting and placing downed trees in bare patches had no initial effect on runoff and erosion processes. Burning initially increased runoff and erosion rates at the sites, but favorable herbaceous cover recruitment two years after burning reduced erosion from the mostly bare intercanopy between tree mounds. Our presentation of the overall study will summarize these published pre-fire, first year, and second year vegetation and hydrologic and erosion responses and preliminary results from the tenth year post-treatment. The collective results greatly advance understanding of pinyon and juniper encroachment on vegetation and hydrologic and erosion processes and the short-term and decadal ecohydrologic impacts of tree removal by cutting, mastication, and burning.