Search

The transition of sagebrush‐dominated (Artemisia spp.) shrublands to pinyon (Pinus spp.) and juniper (Juniperus spp.) woodlands markedly alters resource‐conserving vegetation structure typical of these landscapes. Land managers and scientists in the western United States need knowledge and predictive tools for assessment and effective targeting of tree‐removal treatments to conserve or restore sagebrush vegetation and associated hydrologic function. This study developed modeling approaches to quantify the hydrologic vulnerability and erosion potential of sagebrush rangelands in the later stages of woodland encroachment and in response to commonly applied tree‐removal treatments. Using experimental data from multiple sites in the Great Basin Region, USA, and process‐based knowledge from decade‐long vegetation and rainfall simulation studies at those sites, we (1) assessed the capability of the Rangeland Hydrology and Erosion Model (RHEM) to accurately predict patch‐scale (12 m2) measured runoff and erosion from tree canopy and intercanopy hydrologic functional units in untreated and burned woodlands 9 years postfire, and (2) developed and evaluated multiple RHEM approaches/frameworks to model aggregated effects of tree canopy and intercanopy areas on patch‐ and hillslope‐scale (50 m length) runoff and erosion processes in untreated and treated (burned, cut, and masticated) woodlands. The RHEM accurately predicted measured runoff and sediment yield from patch‐scale rainfall simulations as partitioned on untreated and treated tree canopy and intercanopy areas and effectively parameterized the dominant controls on runoff and erosion process in woodlands. With few exceptions, evaluated hillslope‐scale RHEM frameworks similarly predicted reduced hydrologic vulnerability and erosion potential for conditions 9 years following tree removal by burning, cutting, and mastication treatments. Regressions of RHEM‐predicted hillslope runoff, sediment, and hydraulic/erosion parameters with bare ground and ground cover attributes indicate all RHEM frameworks effectively represented the dominant controls on hydrologic and erosion processes for rangelands and woodlands. The results provide RHEM frameworks and recommendations for assessing hydrologic vulnerability and erosion potential on woodland‐encroached sites and predicting the effectiveness of tree removal to reestablish a water and soil resource‐conserving vegetation structure on sagebrush rangelands. We anticipate our RHEM or similar modeling approaches may be applicable to analogous water‐limited landscapes elsewhere subject to woody plant encroachment. [ABSTRACT FROM AUTHOR]

Rainfall simulation and overland-flow experiments enhance understanding of surface hydrology and erosion processes, quantify runoff and erosion rates, and provide valuable data for developing and testing predictive models. We present a unique dataset (1021 experimental plots) of rainfall simulation (1300 plot runs) and overland-flow (838 plot runs) experimental plot data paired with measures of vegetation, ground cover, and surface soil physical properties spanning point to hillslope scales. The experimental data were collected at three sloping sagebrush (Artemisia spp.) sites in the Great Basin, USA, each subjected to woodland encroachment and with conditions representative of intact wooded shrublands and 1–9 years following wildfire, prescribed fire, and/or tree cutting and shredding tree-removal treatments. The methodologies applied in data collection and the cross-scale experimental design uniquely provide scale-dependent, separate measures of interrill (rain splash and sheet flow processes, 0.5 m 2 plots) and concentrated overland-flow runoff and erosion rates (∼9 m 2 plots), along with collective rates for these same processes combined over the patch scale (13 m 2 plots). The dataset provides a valuable source for developing, assessing, and calibrating/validating runoff and erosion models applicable to diverse plant community dynamics with varying vegetation, ground cover, and surface soil conditions. The experimental data advance understanding and quantification of surface hydrologic and erosion processes for the research domain and potentially for other patchy-vegetated rangeland landscapes elsewhere. Lastly, the unique nature of repeated measures spanning numerous treatments and timescales delivers a valuable dataset for examining long-term landscape vegetation, soil, hydrology, and erosion responses to various management actions, land use, and natural disturbances. The dataset is available from the US Department of Agriculture National Agricultural Library at https://data.nal.usda.gov/search/type/dataset (last access: 7 May 2020) (doi: 10.15482/USDA.ADC/1504518; Pierson et al., 2019). [ABSTRACT FROM AUTHOR]

Wildfire is a natural component of sagebrush (Artemisia spp.) steppe rangelands that induces temporal shifts in plant community physiognomy, ground surface conditions, and erosion rates. Fire alteration of the vegetation structure and ground cover in these ecosystems commonly amplifies soil losses by wind‐ and water‐driven erosion. Much of the fire‐related erosion research for sagebrush steppe has focused on either erosion by wind over gentle terrain or water‐driven erosion under high‐intensity rainfall on complex topography. However, many sagebrush rangelands are geographically positioned in snow‐dominated uplands with complex terrain in which runoff and sediment delivery occur primarily in winter months associated with cold‐season hydrology. Current understanding is limited regarding fire effects on the interaction of wind‐ and cold‐season hydrologic‐driven erosion processes for these ecosystems. In this study, we evaluated fire impacts on vegetation, ground cover, soils, and erosion across spatial scales at a snow‐dominated mountainous sagebrush site over a 2‐year period post‐fire. Vegetation, ground cover, and soil conditions were assessed at various plot scales (8 m2 to 3.42 ha) through standard field measures. Erosion was quantified through a network of silt fences (n = 24) spanning hillslope and side channel or swale areas, ranging from 0.003 to 3.42 ha in size. Sediment delivery at the watershed scale (129 ha) was assessed by suspended sediment samples of streamflow through a drop‐box v‐notch weir. Wildfire consumed nearly all above‐ground live vegetation at the site and resulted in more than 60% bare ground (bare soil, ash, and rock) in the immediate post‐fire period. Widespread wind‐driven sediment loading of swales was observed over the first month post‐fire and extensive snow drifts were formed in these swales each winter season during the study. In the first year, sediment yields from north‐ and south‐facing aspects averaged 0.99–8.62 t ha−1 at the short‐hillslope scale (~0.004 ha), 0.02–1.65 t ha−1 at the long‐hillslope scale (0.02–0.46 ha), and 0.24–0.71 t ha−1 at the swale scale (0.65–3.42 ha), and watershed scale sediment yield was 2.47 t ha−1. By the second year post fire, foliar cover exceeded 120% across the site, but bare ground remained more than 60%. Sediment yield in the second year was greatly reduced across short‐ to long‐hillslope scales (0.02–0.04 t ha−1), but was similar to first‐year measures for swale plots (0.24–0.61 t ha−1) and at the watershed scale (3.05 t ha−1). Nearly all the sediment collected across all spatial scales was delivered during runoff events associated with cold‐season hydrologic processes, including rain‐on‐snow, rain‐on‐frozen soils, and snowmelt runoff. Approximately 85–99% of annual sediment collected across all silt fence plots each year was from swales. The high levels of sediment delivered across hillslope to watershed scales in this study are attributed to observed preferential loading of fine sediments into swale channels by aeolian processes in the immediate post‐fire period and subsequent flushing of these sediments by runoff from cold‐season hydrologic processes. Our results suggest that the interaction of aeolian and cold‐season hydrologic‐driven erosion processes is an important component for consideration in post‐fire erosion assessment and prediction and can have profound implications for soil loss from these ecosystems. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Rainfall simulation and overland-flow experiments enhance understanding of surface hydrology and erosion processes, quantify runoff and erosion rates, and provide valuable data for developing and testing predictive models. We present a unique dataset (1021 experimental plots) of rainfall simulation (1300 plot runs) and overland flow (838 plot runs) experimental plot data paired with measures of vegetation, ground cover, and surface soil physical properties spanning point to hillslope scales. The experimental data were collected at three sloping sagebrush (Artemisia spp.) sites in the Great Basin, USA, each subjected to woodland-encroachment and with conditions representative of intact wooded-shrublands and 1–9 yr following wildfire, prescribed fire, and/or tree cutting and shredding tree-removal treatments. The methodologies applied in data collection and the cross-scale experimental design uniquely provide scale-dependent, separate measures of interrill (rainsplash and sheetflow processes) and concentrated overland-flow runoff and erosion rates along with collective rates for these same processes combined over the patch scale (tens of meters). The dataset provides a valuable source for developing, assessing, and calibrating/validating runoff and erosion models applicable to diverse plant community dynamics with varying vegetation, ground cover, and surface soil conditions. The experimental data advance understanding and quantification of surface hydrologic and erosion processes for the research domain and potentially for other patchy-vegetated rangeland landscapes elsewhere. Lastly, the unique nature of repeated measures spanning numerous treatments and time scales delivers a valuable dataset for examining long-term landscape vegetation, soil, hydrology, and erosion responses to various management actions, land use, and natural disturbances. [ABSTRACT FROM AUTHOR]

The recent increase in wildfire activity across the rangeland-xeric forest continuum in the western United States has landscape-scale consequences in terms of runoff and erosion. Concomitant cheatgrass (Bromus tectorum L.) invasions, plant community transitions and a warming climate in recent decades along grassland-shrubland-woodland-xeric forest transitions have promoted frequent and large wildfires, and continuance of the trend appears likely if warming climate conditions prevail. These changes potentially increase overall hydrologic vulnerability by spatially and temporally increasing soil exposure to runoff and erosion processes. Plot and hillslope-scale studies demonstrate burning may increase event runoff or erosion by factors of 2-40 over small-plot scales and more than 100-fold over large-plot to hillslope scales. Reports of flooding and debris flow events from rangelands and xeric forests following burning show the potential risk to natural resources, property, infrastructure and human life. We present a conceptual model for evaluating post-fire hydrologic vulnerability and risk. We suggest that post-fire risk assessment of potential hydrologic hazards should adopt a probability-based approach that considers varying site susceptibility in conjunction with a range of potential storms and that determines the hydrologic response magnitudes likely to affect values-at-risk. Our review suggests that improved risk assessment requires better understanding in several key areas including quantification of interactions between varying storm intensities and measures of site susceptibility, the varying effects of soil water repellency, and the spatial scaling of post-fire hydrologic response across rangeland-xeric forest plant communities. This paper reviews the potential hydrologic and erosion consequences of increased wildfire activity associated with cheatgrass invasions, plant community transitions and warming climate along the rangeland-xeric forest continuum in the western United States. A conceptual model of post-fire hydrologic vulnerability and risk is presented and key knowledge gaps that limit post-fire risk assessment are identified. [ABSTRACT FROM AUTHOR]

The article provides information on the ecological benefits of mountainous sagebrush landscape on erosion and rill. It presents the effects of climate change, vegetation, and soil water repellency on the wearing out of ground soil. It also discusses the contribution of rainfall simulations and artificial rainfall techniques on burned sites. Moreover, the data shows on the persistence of fire effects on sandy sagebrush. An evaluation of surface-soil and vegetation factors is also tackled. It also uses the analysis of variance (ANOVA) to tests the rainfall simulation plots on burned and unburned brushwood.

The article presents a study on the fire effects on rangeland hydrology and erosion in a steep sagebrush-dominated landscape. It applies a small-plot rainfall and concentrated flow simulations to unburned and burned hillslopes to establish the spatial and temporal persistence of fire-induced impacts on runoff and erosion by interrill and rill processes on steep sagebrush-dominated sites. It compares the Spatial and temporal variability in post-fire hydrologic and erosion responses with runoff and erosion in unburned conditions. Moreover, the comparison signify that the impacts of fire on runoff and erosion from burned steep sagebrush landscapes differ by microsite and process, and that fire-induced increase in runoff and erosion may need more than years to return conditions to level.

Abstract: Fire in sagebrush rangelands significantly alters canopy cover, ground cover, and soil properties which influence runoff and erosion processes. Runoff can be generated more quickly and in larger volume following fire resulting in increased risk of severe erosion and downstream flooding. The Water Erosion Prediction Project (WEPP) model was developed to predict erosion on cropland, forest, and rangeland. WEPP is a tool that has potential to model the effect of fire on hillslope hydrological processes and help managers address erosion and runoff risks following fire. Experimental results on a steep (35 to 50% slope) sagebrush site suggest that rill erosion is the dominant erosion process following fire and the WEPP parameterization equations related to the rill erosion process need improvements. Rill detachment estimates could be improved by modifying regression-estimated values of rill erodibility. Also, the interactions of rill width and surface roughness on soil shear stress estimates may also need to be modified. In this paper we report the effects of prescribed fire on runoff, soil erosion, and rill hydraulics and compare WEPP estimated erosion for several modeling options with measured erosion. [Copyright &y& Elsevier]

Pinyon (Pinus spp.) and juniper (Juniperus spp.) woodland encroachment into sagebrush (Artemisia spp.) steppe communities throughout western North America has substantially altered the vegetation structure and hydrologic function of one of the most ecologically important rangeland ecosystems in the world. Various pinyon and juniper tree removal practices are employed to re-establish sagebrush steppe vegetation and an associated resource-conserving ecohydrologic function. The effectiveness of these practices is highly variable owing to the vast domain in which woodland encroachment occurs, climate fluctuations, differences in treatment applications, and myriads of pre-treatment conditions and post-treatment land uses. This study evaluated the long-term (13 years post-treatment) effectiveness of prescribed fire and mechanical tree removal to re-establish sagebrush steppe vegetation and associated spatial patterns in ground surface conditions and soil hydrologic properties of two woodland-encroached sites. Specifically, we assessed the effects of tree removal on: (1) vegetation and ground cover at the hillslope scale (990 m2 plots) and (2) associated spatial patterns in point-scale ground surface conditions and soil hydrologic properties along transects extending from tree bases and into the intercanopy areas between trees. Both sites were in mid to late stages of woodland encroachment with extensive bare conditions (~60–80% bare ground) throughout a degraded intercanopy area (~75% of the domain) surrounding tree islands (~25% of domain, subcanopy areas). All treatments effectively removed mature tree cover and increased hillslope vegetation. Enhanced herbaceous cover (4–15-fold increases) in burned areas reduced bare interspace (bare area between plants) by at least 4-fold and improved intercanopy hydraulic conductivity (> than 2-fold) and overall ecohydrologic function. Mechanical treatments retained or increased sagebrush and generally increased the intercanopy herbaceous vegetation. Intercanopy ground surface conditions and soil hydrologic properties in mechanical treatments were generally similar to those in burned areas but were also statistically similar to the same measures in untreated areas in most cases. This suggests that vegetation and ground surface conditions in mechanical treatments are trending toward a significantly improved hydrologic function over time. Treatments had limited impact on soil hydrologic properties within subcanopy areas; however, burning did reduce the soil water repellency strength and the occurrence of strong soil water repellency underneath trees by three- to four-fold. Overall, the treatments over a 13-year period enhanced the vegetation, ground surface conditions, and soil hydrologic properties that promote infiltration and limit runoff generation for intercanopy areas representing ~75% of the area at the sites. However, ecological tradeoffs in treatment alternatives were evident. The variations in woodland responses across sites, treatments, and measurement scales in this long-term study illustrate the complexity in predicting vegetation and hydrologic responses to tree removal on woodland-encroached sagebrush sites and underpin the need and value of multi-scale long-term studies. [ABSTRACT FROM AUTHOR]

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]

Encroachment of sagebrush (Artemisia spp.) shrublands by pinyon (Pinus spp.) and juniper (Juniperus spp.) conifers (woodland encroachment) induces a shift from biotic‐controlled resource retention to abiotic‐driven loss of soil resources. This shift is driven by a coarsening of the vegetation structure with increasing dominance of site resources by trees. Competition between the encroaching trees and understory vegetation for limited soil and water resources facilitates extensive bare intercanopy area between trees and concomitant increases in run‐off and erosion that, over time, propagate persistence of the shrubland‐to‐woodland conversion. We evaluated whether tree removal by burning can decrease late‐succession woodland ecohydrologic resilience by increasing vegetation and ground cover over a 9‐year period after fire and whether the soil erosion feedback on late‐succession woodlands is reversible by burning. To address these questions, we employed a suite of vegetation and soil measurements and rainfall simulation and concentrated overland flow experiments across multiple plot scales on unburned and burned areas at two sagebrush sites in the later stages of woodland succession. Prior to burning, tree cover was approximately 28% at the sites, and more than 70% of the area at the sites was intercanopy with depauperate understory vegetation and extensive bare ground (52–60% bare soil and rock). Burning initially increased bare ground across fine (<1 m2) to patch (tens of metres) scales, resulting in enhanced sediment availability at the fine scale, sustained high run‐off and erosion within degraded intercanopies, amplified run‐off and erosion from tree canopy areas, and amplified sediment delivery across fine to patch scales. However, fire‐induced increases in grass cover over nine growing seasons improved infiltration, limited run‐off and sediment delivery from the fine scale, and reduced intercanopy run‐off and erosion at the patch scale. These changes reflect a switch in vegetation structure, triggered by burning and subsequent vegetation re‐establishment, and a shift to biotic control on run‐off and erosion across spatial scales. The responses and persistence over the 9‐year period postfire at the two sites demonstrate that fire can decrease woodland ecohydrologic resilience by altering plant community physiognomy and thereby can reverse the soil erosion feedback on sagebrush shrublands in the later stages of woodland encroachment. [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]