Long-term impacts of pinyon-juniper removal on vegetation and hydrologic properties

Authors: BURLESON, C. - University Of Arizona; JOHNSON, J. - University Of Arizona; Williams, Christopher - Jason; Polyakov, Viktor; Pierson Jr, Frederick

Submitted to: Society for Range Management
Publication Type: Abstract Only
Publication Acceptance Date: 12/12/2019
Publication Date: 2/16/2020
Citation: Burleson, C., Johnson, J., Williams, C.J., Polyakov, V.O., Pierson Jr, F.B. 2020. Long-term impacts of pinyon-juniper removal on vegetation and hydrologic properties. Presented at the 73rd Annual SRM Meeting, Transformation and Translation, Society for Range Management, February, 16-20, 2020, Denver, CO, Poster Number 42.

Interpretive Summary: Throughout the western U.S., extensive pinyon-juniper (Pinus spp., Juniperus spp.) encroachment into sagebrush (Artemisia spp.) shrublands has reduced sagebrush habitat and modified hydrologic function. Land managers are combating this challenge with tree removal treatments to return current woodlands to historical sagebrush shrublands. This study examines the effects of fire and mechanical tree-removal treatments on vegetation as well as the spatial patterns and persistence of litter accumulation and soil hydrologic properties along hillslopes. Experimental plots were located at three sites in the Great Basin region. Vegetation sampling was completed pre-treatment (2006) and 1, 9, and 13 years after mechanical and prescribed-fire treatments at two sites. Sampling was also conducted in a naturally burned and unburned third site two consecutive years after a wildfire (2008, 2009). In 2019, hydrologic, soil, and vegetation characteristics were sampled in canopy and intercanopy microsites within all treatments at each site. All treatments were effective in reducing tree cover. Over a period of 13 years, sagebrush and perennial grass cover increased in mechanical treatments and perennial and annual grass cover increased in prescribed fire treatments. Wildfire initially reduced perennial grass cover 4-fold and removed 100% of the limited pre-fire shrub cover. Perennial grasses increased 3-fold over the 2nd year after wildfire, but shrub cover remained near 0%. In 2019, soil water repellency was observed on former and existing tree microsites in all treatment areas, but repellency adjacent to standing dead trees and stumps within burned treatment areas was weaker than in tree microsites within untreated and mechanically treated areas. With few exceptions, ground cover was generally greater in treated intercanopy areas than in untreated areas. While treatment effects vary by treatment type, the preliminary results indicated that pinyon-juniper removal treatments can increase vegetation and ground cover, reduce soil water repellency, and improve surface conditions on sagebrush rangelands.

Technical Abstract: Throughout the western U.S., extensive pinyon-juniper (Pinus spp., Juniperus spp.) encroachment into sagebrush (Artemisia spp.) shrublands has reduced sagebrush habitat and modified hydrologic function. Land managers are combating this challenge with tree removal treatments to return current woodlands to historical sagebrush shrublands. This study examines the effects of fire and mechanical tree-removal treatments on vegetation as well as the spatial patterns and persistence of litter accumulation and soil hydrologic properties along hillslopes. Experimental plots were located at three sites in the Great Basin region. Vegetation sampling was completed pre-treatment (2006) and 1, 9, and 13 years after mechanical and prescribed-fire treatments at two sites. Sampling was also conducted in a naturally burned and unburned third site two consecutive years after a wildfire (2008, 2009). In 2019, hydrologic, soil, and vegetation characteristics were sampled in canopy and intercanopy microsites within all treatments at each site. All treatments were effective in reducing tree cover. Over a period of 13 years, sagebrush and perennial grass cover increased in mechanical treatments and perennial and annual grass cover increased in prescribed fire treatments. Wildfire initially reduced perennial grass cover 4-fold and removed 100% of the limited pre-fire shrub cover. Perennial grasses increased 3-fold over the 2nd year after wildfire, but shrub cover remained near 0%. In 2019, soil water repellency was observed on former and existing tree microsites in all treatment areas, but repellency adjacent to standing dead trees and stumps within burned treatment areas was weaker than in tree microsites within untreated and mechanically treated areas. With few exceptions, ground cover was generally greater in treated intercanopy areas than in untreated areas. While treatment effects vary by treatment type, the preliminary results indicated that pinyon-juniper removal treatments can increase vegetation and ground cover, reduce soil water repellency, and improve surface conditions on sagebrush rangelands.