Effectiveness of prescribed fire to re-establish sagebrush vegetation and ecohydrologic function on woodland-encroached sagebrush steppe, Great Basin, USA

Authors: Williams, Christopher - Jason; Pierson Jr, Frederick; Kormos, Patrick; AL-HAMDAN, O.Z. - Texas A&M University; NOUWAKPO, S.K. - University Of Nevada; Weltz, Mark; VEGA, S. - University Of Idaho; LINDSAY, K. - Us Bureau Of Reclamation

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 10/3/2017
Publication Date: 12/11/2017
Citation: Williams, C.J., Pierson Jr, F.B., Kormos, P.R., Al-Hamdan, O., Nouwakpo, S., Weltz, M.A., Vega, S., Lindsay, K. 2017. Effectiveness of prescribed fire to re-establish sagebrush vegetation and ecohydrologic function on woodland-encroached sagebrush steppe, Great Basin, USA. American Geophysical Union, December 11-15, 2017, San Francisco, CA. #H21B-1457.

Interpretive Summary: Range expansion of pinyon (Pinus spp.) and juniper (Juniperus spp.) conifers into sagebrush steppe (Artemisia spp.) communities has imperiled a vast domain in the western US. The sagebrush ecosystem once extended over 620,000 km2 of the western US by some accounts and currently occupies less than 60% of its historical range. Pinyon and juniper woodlands now occupy an estimated 190,000 km2 in the Intermountain Western US and about 90% of that domain was historically occupied by sagebrush vegetation. Much of the pinyon- and juniper-dominated shrublands in the western US are at risk to high severity wildfire due to dense woody fuels or conversion to a degraded state dominated by invasive annual grasses following wildfire. Encroachment of sagebrush ecosystems by pinyon and juniper conifers has negative ramifications to ecosystem structure and function and delivery of goods and services. Scientists, land management agencies, and private land owners throughout the western US are challenged with selecting from a suite of options to reduce pinyon and juniper woody fuels and re-establish sagebrush steppe structure and function. This study evaluated the effectiveness of prescribed fire to re-establish sagebrush vegetation and ecohydrologic function over a 9 yr period. Nine years post-fire hydrologic and erosion responses reflect the combination of pre-fire site conditions, perennial grass recruitment, delayed litter cover, and inherent site characteristics. Burning initially increased bare ground, runoff, and erosion for well-vegetated areas underneath tree and shrub canopies, but had minimal impact on hydrology and erosion for degraded interspaces between plants. The degraded interspaces were primarily bare ground and exhibited high runoff and erosion rates prior to burning. Initial fire effects persisted for two years, but increased productivity of grasses improved hydrologic function of interspaces over the full 9 yr period. At the hillslope scale, grass recruitment in the intercanopy between trees reduced runoff from rainsplash, sheetflow, and concentrated overland flow at one site, but did not reduce the high levels of runoff and erosion from a more degraded site. In areas formerly occupied by trees (tree zones), burning increased invasive annual grass cover due to fire removal of limited native perennial plants and competition for resources. The invasive annual grass cover had no definitive negative effect on runoff and erosion from tree zones however. Runoff and erosion increased in tree zones at the more degraded site due to delayed litter recruitment and persistence of bare ground conditions. Overall, the 9 yr study illustrates the ecohydrologic complexities with predicting sagebrush ecosystem responses to woodland encroachment and tree removal and provides increased understanding of fire as a tool to re-establish sagebrush vegetation and ecohydrologic function on woodland encroached sites in the Great Basin.

Technical Abstract: Range expansion of pinyon (Pinus spp.) and juniper (Juniperus spp.) conifers into sagebrush steppe (Artemisia spp.) communities has imperiled a vast domain in the western US. The sagebrush ecosystem once extended over 620,000 km2 of the western US by some accounts and currently occupies less than 60% of its historical range. Pinyon and juniper woodlands now occupy an estimated 190,000 km2 in the Intermountain Western US and about 90% of that domain was historically occupied by sagebrush vegetation. Much of the pinyon- and juniper-dominated shrublands in the western US are at risk to high severity wildfire due to dense woody fuels or conversion to a degraded state dominated by invasive annual grasses following wildfire. Encroachment of sagebrush ecosystems by pinyon and juniper conifers has negative ramifications to ecosystem structure and function and delivery of goods and services. Scientists, land management agencies, and private land owners throughout the western US are challenged with selecting from a suite of options to reduce pinyon and juniper woody fuels and re-establish sagebrush steppe structure and function. This study evaluated the effectiveness of prescribed fire to re-establish sagebrush vegetation and ecohydrologic function over a 9 yr period. Nine years post-fire hydrologic and erosion responses reflect the combination of pre-fire site conditions, perennial grass recruitment, delayed litter cover, and inherent site characteristics. Burning initially increased bare ground, runoff, and erosion for well-vegetated areas underneath tree and shrub canopies, but had minimal impact on hydrology and erosion for degraded interspaces between plants. The degraded interspaces were primarily bare ground and exhibited high runoff and erosion rates prior to burning. Initial fire effects persisted for two years, but increased productivity of grasses improved hydrologic function of interspaces over the full 9 yr period. At the hillslope scale, grass recruitment in the intercanopy between trees reduced runoff from rainsplash, sheetflow, and concentrated overland flow at one site, but did not reduce the high levels of runoff and erosion from a more degraded site. In areas formerly occupied by trees (tree zones), burning increased invasive annual grass cover due to fire removal of limited native perennial plants and competition for resources. The invasive annual grass cover had no definitive negative effect on runoff and erosion from tree zones however. Runoff and erosion increased in tree zones at the more degraded site due to delayed litter recruitment and persistence of bare ground conditions. Overall, the 9 yr study illustrates the ecohydrologic complexities with predicting sagebrush ecosystem responses to woodland encroachment and tree removal and provides increased understanding of fire as a tool to re-establish sagebrush vegetation and ecohydrologic function on woodland encroached sites in the Great Basin.