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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 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, public land management agencies, and private land owners are challenged with selecting and predicting outcomes to treatment alternatives to improve ecological structure and function on 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. For untreated conditions, extensive bare interspace (87% bare ground) throughout the degraded intercanopy (69–88% bare ground) between trees at both sites promoted high runoff and sediment yield from combined rainsplash and sheetflow (~45 mm, 59–381 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 canopy cover of native perennial herbaceous vegetation by >5-fold, on average, across both sites over nine growing seasons. Burning reduced low pre-fire sagebrush canopy cover (<1% to 14% average) 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 at both sites. Fire-induced increases in herbaceous canopy cover (from 34% 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 (371 L to 266 L) and sediment yield (3015 g to 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 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%, on average, post-fire across the sites and was primarily restricted to areas around burned trees. High herbaceous cover (73%) under burned trees at the less degraded site resulted in similar low total runoff and sediment from concentrated flow experiments 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) from concentrated flow experiments in burned tree areas at the more degraded site. The experimental results demonstrate 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 site suggest results should be interpreted with caution however. Although burning substantially increased perennial grass cover and reduced fine-scale runoff and erosion at the more degraded site, poor sagebrush recovery, delayed litter recruitment, and persistent high concentrated flow erosion at that site suggest not all sites are good candidates for prescribed fire treatments. Furthermore, high levels of cheatgrass in burned tree areas (~30% of area) at both sites increases wildfire risk, but cheatgrass is expected to decline over time in absence of fire. Our results in context with the literature suggest fire-surrogate tree-removal treatments (e.g., tree cutting or shredding) may be more appropriate on degraded sites with limited pre-treatment sagebrush and perennial herbaceous vegetation and that seeding may be necessary to improve post-fire establishment of sagebrush steppe vegetation structure and associated ecohydrologic function under these conditions. Lastly, vegetation, runoff, and erosion responses in this study are not directly applicable outside of the Great Basin, but similar responses in woodland studies from the southwestern US suggest potential application of results to woodlands in that region. The concept of re-establishing vegetation structure to improve ecohydrologic function is broadly applicable to sparsely vegetated lands around the World. • Burning increased grass in the bare intercanopy at two woodlands 9 yr post-fire. • Grass increases improved infiltration and erosion in degraded interspaces (0.5 m2). • Litter regulated overland flow whereas runoff and flow velocity controlled erosion. • Increased grass and litter reduced intercanopy (9 m2) runoff and erosion at 1 site. • More degraded initial conditions limited ecological improvements at a 2nd site. [ABSTRACT FROM AUTHOR]

• Prescribed fire promoted herbaceous growth in bare interspaces. • Litter enhanced infiltration and provided protection against erosion. • Increased vegetation cover altered flow paths and reduced runoff and soil loss. • Reduced soil surface connectivity post-fire improved hydrologic function. • Hydrologic function continues to improve 9 yr after fire. Woody species encroachment into herbaceous and shrub-dominated vegetations is a concern in many rangeland ecosystems of the world. Arrival of woody species into affected rangelands leads to changes in the spatial structure of vegetation and alterations of biophysical processes. In the western USA, encroachment of pinyon (Pinus spp.) and juniper (Juniperus spp.) tree species into sagebrush steppes poses a threat to the proper ecohydrological functioning of these ecosystems. Prescribed fire has been proposed and used as one rangeland improvement practice to restore sagebrush steppe from pinyon-juniper encroachment. Short-term effects of burning on the ecohydrologic response of these systems have been well documented and often include a period of increased hydrologic and erosion vulnerability immediately after burning. Long-term ecohydrologic response of sagebrush steppe ecosystems to fire is poorly understood due to lack of cross-scale studies on treated sites. The aim of this study is to evaluate long-term vegetation, hydrologic, and erosion responses at two pinyon-juniper-encroached sagebrush sites 9 years after prescribed fire was applied as a restoration treatment. Thirty-six rainfall simulation experiments on 6 m × 2 m plots were conducted for 45 min under two conditions: a dry run (70 mm h−1; dry antecedent soils) and a wet run (111 mm h−1; wet antecedent soils). Runoff and erosion responses were compared between burned and unburned plots. Overall, increases in herbaceous cover in the shrub-interspace areas (intercanopy area between trees) at both sites 9 years post-burn resulted in runoff- and erosion-reduction benefits, especially under the wet runs. While the initially more degraded site characterized by 80% bare ground pre-burn, registered a higher overall increase (40% increase) in canopy cover, greater post-fire reductions in runoff and erosion were observed at the less degraded site (57% bare ground pre-burn). Runoff and erosion for the wet runs decreased respectively by 6.5-fold and 76-fold at the latter site on the burned plots relative to control plots, whereas these decreases were more muted at the more degraded site (2.5 and 3-fold respectively). Significant fragmentation of flow paths observed at the more-degraded site 9 years post-fire, suggests a decreased hydrologic connectivity as a mechanism of runoff and erosion reduction during post-fire recovery. [ABSTRACT FROM AUTHOR]