Effectiveness of prescribed fire to re-establish sagebrush steppe vegetation and ecohydrologic function on woodland-encroached sagebrush rangelands, Great Basin, USA: Part I: Vegetation, hydrology, and erosion responses

Authors: Williams, Christopher - Jason; Pierson Jr, Frederick; Nouwakpo, Sayjro; AL-HAMDAN, O.Z. - Texas A&M University; Kormos, Patrick; Weltz, Mark

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2018
Publication Date: 4/25/2018
Publication URL: http://handle.nal.usda.gov/10113/6357105
Citation: Williams, C.J., Pierson, F.B., Nouwakpo, S., Al-Hamdan, O., Kormos, P.R., Weltz, M.A. 2018. Effectiveness of prescribed fire to re-establish sagebrush steppe vegetation and ecohydrologic function on woodland-encroached sagebrush rangelands, Great Basin, USA: Part I: Vegetation, hydrology, and erosion responses. Catena. https://doi.org/10.1016/j.catena.2018.02.027.
DOI: https://doi.org/10.1016/j.catena.2018.02.027

Interpretive Summary: Pinyon and juniper tree encroachment into sagebrush communities can negatively impact vegetation, hydrology and erosion processes and thereby affect delivery of ecosystem goods and services. Current knowledge of the long-term effectiveness of tree removal treatments to mitigate negative impacts of tree encroachment is inadequate to inform land managers and guide management of these ecosystems. This study used vegetation measures, rainfall simulations, and overland flow experiments to evaluate the impact of tree removal by prescribed fire on vegetation and hydrology and erosion processes at two sites 9 yr after tree removal. Burning was effective at re-establishing native grasses important in the restoration of sagebrush communities, but also promoted scattered patches of invasive annual grasses. Tree removal improved hydrologic function at one of the sites, but had more limited impact on hydrology and erosion at a second more degraded site. The experimental results from the less degraded site suggest pinyon and juniper removal by prescribed fire can effectively re-establish a trajectory towards sagebrush steppe vegetation and hydrologic recovery. Responses at the second, more degraded site, indicate recovery of tree-encroached sagebrush vegetation and hydrology through prescribed fire treatments can require more than 9 yr. The study advances knowledge regarding the impacts of prescribed fire for tree removal on sagebrush sites with dense pinyon and juniper cover and provides strategies to increase the rate of vegetation and hydrologic recovery for this imperiled ecosystem through tree removal.

Technical Abstract: Pinyon (Pinus spp.) and juniper (Juniperus spp.) woodland encroachment has imperiled a broad ecological domain of the sagebrush steppe (Artemisia spp.) ecosystem in the Great Basin Region, USA. As these conifers increase in dominance on sagebrush rangelands, understory vegetation commonly declines and ecohydrologic function can shift from biotic (vegetation) controlled retention of soil resources to abiotic (runoff) driven loss of soil resources and long-term site degradation. Scientists, governmental land management agencies, and private land owners are challenged with selection of and predicting outcomes to numerous treatment alternatives to improve ecological structure and function of these rangelands. This study is the first of a two-part study to evaluate effectiveness of prescribed fire to re-establish sagebrush steppe vegetation and improve ecohydrologic function on mid- to late-succession pinyon-and juniper-encroached sagebrush sites in the Great Basin. We used a suite of vegetation and soil measures, small-plot (0.5 m2) rainfall simulations, and overland flow experiments (9 m2) to quantify the effects of tree removal by prescribed fire on vegetation, soils, and rainsplash, sheetflow, and concentrated flow hydrologic and erosion processes at two woodlands 9-yr after burning. Prior to burning, extensive bare interspace (69-88% bare ground) in the degraded intercanopy between trees at both sites generated high levels of runoff and sediment yield from combined rainsplash and sheetflow (~45 mm, 60-381 g m-2) and concentrated flow (371-501 L, 2343-3015 g) processes during high intensity rainfall simulation (102 mm h-1, 45 min) and overland flow experiments (15, 30, and 45 L min-1, 8 min each). Burning increased native perennial vegetation by nearly 6-fold (from 5% to 29%), on average, across both sites over nine growing seasons. Burning reduced low (<1% to 14%) pre-fire sagebrush canopy cover at both sites and sagebrush recovery is expected to take >30 yr. Enhanced herbaceous cover in interspaces post-fire reduced runoff and sediment yield from high intensity rainfall simulations by 2-fold. Fire-induced increases in herbaceous cover (from 33% to 62%) and litter ground cover (from 15% to 36%) reduced total runoff (from 501 L to 180 L) and sediment yield (from 2343 g to 115 g) from concentrated flow experiments in the intercanopy at one site. Sparser herbaceous vegetation (49% cover) and litter cover (8%) in the intercanopy at the other, more degraded site post-fire resulted in no significant reduction of total runoff (266 L) and sediment yield (1982 g) for concentrated flow experiments. Areas underneath unburned shrub and tree canopies were well covered by vegetation and ground cover and generated limited runoff and sediment. Fire impacts on vegetation, ground cover, and runoff and sediment delivery from tree and shrub rainfall plots were highly variable. Burning litter covered areas underneath trees reduced perennial herbaceous vegetation and increased invasibility to the fire-prone annual cheatgrass (Bromus tectorum L.). Cheatgrass cover increased from <1% pre-fire to 16-30% post-fire across the sites and was primarily restricted to rings around burned trees. High herbaceous cover (73%) under burned trees at the less degraded site resulted in similar low total runoff and sediment as pre-fire (136-228 L, 204-423 g). In contrast, fire-reduction of litter (from 79% to 49%) resulted in increased total runoff (from 103 L to 333 L) and sediment yield (from 619 g to 2170 g) after burning tree areas at the more degraded site. The experimental results from the less degraded site suggest pinyon and juniper removal by prescribed fire can effectively re-establish a successional trajectory towards sagebrush steppe vegetation structure and thereby improve ecohydrologic function. Responses to burning at the more degraded