Pinon-juniper reduction increases soil water availability of the resouce growth pool

Authors: ROUNDY, BRUCE - Brigham Young University; YOUNG, KERT - Brigham Young University; CLINE, NATHAN - Brigham Young University; Hulet, April; MILLER, RICHARD - Oregon State University; TAUSCH, ROBIN - Us Forest Service (FS); CHAMBERS, JEANNE - Us Forest Service (FS); Rau, Benjamin

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2013
Publication Date: 9/1/2014
Publication URL: http://handle.nal.usda.gov/10113/60846
Citation: Roundy, B.A., Young, K., Cline, N., Hulet, A., Miller, R.F., Tausch, R.J., Chambers, J.C., Rau, B.M. 2014. Pinon-juniper reduction increases soil water availability of the resouce growth pool. Rangeland Ecology and Management. 67:495-505. DOI: 10.2111/REM-D-13-00022.1.

Interpretive Summary: A major concern for using prescribed fire or mechanical treatments to reduce piñon and juniper trees that are encroaching into sagebrush communities is that invasive weeds, such as cheatgrass, can subsequently dominate and cause recurrent fire. Trees, shrubs, and perennial and annual herbaceous species in these communities all depend on soil water for nutrient diffusion to roots and major growth in spring. We measured the effects of initial tree infilling and fuel control treatments of prescribed fire, tree cutting and tree shredding on time of available water and soil temperature on 11-sites across the Great Basin. Both prescribed fire and mechanical treatments increased the time of available water in spring, with the greatest increase occurring when treatments were applied to a high phase of infilling. To increase resistance to invasive annual grasses managers should treat infilling areas when there is still high enough cover of desirable residual grasses, forbs, and shrubs to use increased resources from tree reduction, and reduce the risk of resource use and dominance by invasive species.

Technical Abstract: Managers reduce piñon (Pinus spp.) and juniper (Juniperus spp.) trees that are encroaching into (Artemisia spp.) communities to lower fuel loads and to increase cover and density of desirable understory species. A major concern for using prescribed fire or mechanical treatments to reduce trees is that invasive weeds, such as cheatgrass (Bromus tectorum L.), can subsequently dominate and cause recurrent fire. Trees, shrubs, and perennial and annual herbaceous species in these communities all depend on soil water held at >-1.5 MPa matric potential in the upper 0.3 m of soil for nutrient diffusion to roots and major growth in spring (resource growth pool). We measured soil water matric potentials and temperatures using gypsum blocks and thermocouples buried at 1-30 cm on tree, shrub, and interspace microsites to characterize the seasonal soil climate of 13 tree-encroached sites across the Great Basin. We also tested the effects of initial tree infilling and fuel control treatments of prescribed fire, tree cutting and tree shredding on time of available water and soil temperature of the resource growth pool on 11 sites. Both prescribed fire and mechanical tree reduction increased the time of available water in spring, but this increase was greatest (up to 26 days) when treatments were applied at a high phase of infilling. To increase resistance to invasive annual grasses managers should treat infilling areas when there is still high enough cover of desirable residual grasses, forbs, and shrubs to use increased resources from tree reduction and reduce the risk of resource use and dominance by invasive species. This strategy is especially critical on warmer sites which have high climate suitability to cheatgrass.