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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]

Cross‐scale structural and functional connectivity feedbacks can amplify exogenous forces in dryland environments leading to ecosystem state change (e.g., from grassland to shrubland). Attenuation of these connectivity feedbacks would ostensibly be required to restore transitioned ecosystems to their former state. We compared structural, hydrologic, and sediment connectivity on a shrub‐encroached semi‐arid grassland in south‐eastern Arizona, USA, to that of a nearby site experiencing an increase in non‐native perennial grass (Lehmann lovegrass) abundance 5‐year following treating shrubs with tebuthiuron herbicide. Soil/vegetation attributes were quantified and paired with hydrologic experiments at fine (0.5 m2) to hillslope (50 m2) scales. Fine‐scale rainfall simulations (120 mm·h−1 rainfall intensity; 45 min) showed interspaces between shrubs were hydrologically similar on the treated and control sites, whereas herbicided shrub patches were more resource conserving than those within the control (terminal infiltration rates of 105 and 71 mm·h−1, respectively). High structural connectivity of bare ground (basal gap lengths >200 cm) was correlated with increased concentrated flow run‐off and accompanied by greater sediment yields within the untreated site at a coarse scale (~9 m2). Hillslope‐scale modelling suggested a divergence between hydrologic and sediment connectivity: run‐off from high intensity rainfall was similar between sites, while predicted sediment yield was 44% less within the tebuthiuron‐treated site. Our results indicate (i) hydraulic properties of soils between shrubs are unresponsive to herbicide treatment, (ii) disruption of structural connectivity of these interspaces associated with grass cover increases subsequent to herbicide application attenuated run‐off and the energy needed for sediment transport, and (iii) sediment connectivity is reduced by conversion to a novel grassland ecological state. [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]

In this study, we present the improved Rangeland Hydrology and Erosion Model (RHEM V2.3), a process-based erosion prediction tool specific for rangeland application. The article provides the mathematical formulation of the model and parameter estimation equations. Model performance is assessed against data collected from 23 runoff and sediment events in a shrub-dominated semiarid watershed in Arizona, USA. To evaluate the model, two sets of primary model parameters were determined using the RHEM V2.3 and RHEM V1.0 parameter estimation equations. Testing of the parameters indicated that RHEM V2.3 parameter estimation equations provided a 76% improvement over RHEM V1.0 parameter estimation equations. Second, the RHEM V2.3 model was calibrated to measurements from the watershed. The parameters estimated by the new equations were within the lowest and highest values of the calibrated parameter set. These results suggest that the new parameter estimation equations can be applied for this environment to predict sediment yield at the hillslope scale. Furthermore, we also applied the RHEM V2.3 to demonstrate the response of the model as a function of foliar cover and ground cover for 124 data points across Arizona and New Mexico. The dependence of average sediment yield on surface ground cover was moderately stronger than that on foliar cover. These results demonstrate that RHEM V2.3 predicts runoff volume, peak runoff, and sediment yield with sufficient accuracy for broad application to assess and manage rangeland systems. [ABSTRACT FROM AUTHOR]

Probit models for estimating hydrothermal germination rate yield model parameters that have been associated with specific physiological processes. The desirability of linking germination response to seed physiology must be weighed against expectations of model fit and the relative accuracy of predicted germination response. Computationally efficient empirical models have been proposed that do not require a priori assumptions about model shape parameters, but the accuracy of these models has not been compared to the more common probit-optimization procedure. Thirteen seedlots, representing six native perennial rangeland grasses and an invasive annual weed, were germinated over the constant temperature range of 3 to 36°C and water potential range of 0 to -2.5 MPa. Hydrothermal germination models were generated using probit optimization, optimized regression, and statistical gridding. These models were evaluated for the pattern and magnitude of residual model error and the relative magnitude of predictive errors under field-simulated temperature and moisture conditions. Residual model errors in predictions of germination rate were greatest for the probit optimization procedure. Statistical gridding and optimized regression produced lower predictive model error, but the latter procedure could not resolve germination response for slower-germinating seed populations. The more computationally efficient and accurate regression and statistical-gridding procedures may be desirable for identifying germination strategies and syndromes that are based on predicted response to simulated conditions of field temperature and moisture. [ABSTRACT FROM AUTHOR]

The rangeland hydrology and erosion model (RHEM) is a new process-based model developed by the USDA Agricultural Research Service. RHEM was initially developed for functionally intact rangelands where concentrated flow erosion is minimal and most soil loss occurs by rain splash and sheet flow erosion processes. Disturbance such as fire or woody plant encroachment can amplify overland flow erosion by increasing the likelihood of concentrated flow formation. In this study, we enhanced RHEM applications on disturbed rangelands by using a new approach for the prediction and parameterization of concentrated flow erosion. The new approach was conceptualized based on observations and results of experimental studies on rangelands disturbed by fire and/or by tree encroachment. The sediment detachment rate for concentrated flow was calculated using soil erodibility and hydraulic (flow width and stream power) parameters. Concentrated flow width was calculated based on flow discharge and slope using an equation developed specifically for disturbed rangelands. Soil detachment was assumed to begin with concentrated flow initiation. A dynamic erodibility concept was applied where concentrated flow erodibility was set to decrease exponentially during a run-off event because of declining sediment availability. Erodibility was estimated using an empirical parameterization equation as a function of vegetation cover and surface soil texture. A dynamic partial differential sediment continuity equation was used to model the total detachment rate of concentrated flow and rain splash and sheet flow. The enhanced version of the model was evaluated against rainfall simulation data for three different sites that exhibit some degree of disturbance by fire and/or by tree encroachment. The coefficient of determination ( R2) and Nash-Sutcliffe efficiency were 0.78 and 0.71, respectively, which indicates the capability of the model using the new approach for predicting soil loss on disturbed rangeland. By using the new concentrated flow modelling approach, the model was enhanced to be a practical tool that utilizes readily available vegetation and soil data for quantifying erosion and assessing erosion risk following rangeland disturbance. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

ABSTRACT Woody plant encroachment on water-limited lands can induce a shift from biotic (plant)-controlled resource retention to abiotic (physical)-driven losses of critical soil resources. The biotic-to-abiotic shift occurs where encroachment propagates connectivity of runoff processes and amplified cross-scale erosion that, in-turn, promote ecohydrologic resilience of the post-encroachment community. We investigated these relationships for woodland-encroached sagebrush steppe in the Great Basin, USA, and evaluated wildfire as a mechanism to reverse the post-encroachment soil erosion feedback. We measured vegetation, soil properties, and runoff/erosion from experimental plots on burned and unburned areas of a late-succession woodland 1 and 2 years post-fire. Our findings suggest that the biotic-to-abiotic shift and amplified cross-scale erosion occur where encroachment-induced bare ground exceeds 50-60% and bare gaps between plant bases frequently extend beyond 1 m. The trigger for amplified cross-scale erosion is formation of concentrated flow within the degraded intercanopy between trees. Burning in this study decreased ecohydrologic resilience of the late-succession woodland through herbaceous recruitment 2 years post-fire. Increased intercanopy herbaceous productivity decreased connectivity of bare ground, improved infiltration, and reduced erosion, but the study site remained vulnerable to runoff and erosion from high-intensity rainfall. We conclude that burning can reduce woodland ecohydrologic resilience and that woodland encroachment-induced structural and functional ecohydrologic attributes may persist during high-intensity storms for an undetermined period post-fire. We cannot conclude whether wildfire reverses the woodland-induced soil erosion feedback on sagebrush rangelands. However, our results suggest that wildfire may provide a restoration pathway for sagebrush steppe by reducing woodland ecohydrologic resilience over time. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Current physically based overland flow erosion models for rangeland application do not separate disturbed and undisturbed conditions in modeling concentrated flow erosion. In this study, concentrated flow simulations on disturbed and undisturbed rangelands were used to estimate the erodibility and to evaluate the performance of linear and power law equations that describe the relationship between erosion rate and several hydraulic parameters. None of the hydraulic parameters consistently predicted the detachment capacity well for all sites, however, stream power performed better than most of other hydraulic parameters. Using power law functions did not improve the detachment relation with respect to that of the linear function. Concentrated flow erodibility increased significantly when a site was exposed to a disturbance such as fire or tree encroachment into sagebrush steppe. This study showed that burning increases erosion by amplifying the erosive power of overland flow through removing obstacles and by changing the soil properties affecting erodibility itself. However, the magnitude of fire impact varied among sites due to inherent differences in site characteristics and variability in burn severity. In most cases we observed concentrated flow erodibility had a high value at overland flow initiation and then started to decline with time due to reduction of sediment availability. Thus we developed an empirical function to predict erodibility variation within a runoff event as a function of cumulative unit discharge. Empirical equations were also developed to predict erodibility variation with time postdisturbance as a function of readily available vegetation cover and surface soil texture data. [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.

This article discusses the use of soil erosion barriers after the Valley Complex Fire in Montana in 2000. The authors measured the postfire runoff and erosion of straw wattle, contour-felled log, and hand-dug contour trench erosion barriers. Runoff from simulated rainfall was significantly less from straw wattle, and contour-felled log compared to controls. Total sediment yield was also less for the straw wattle. The total available storage capacity was greater than the erosion barrier sediment storage used.

Focuses on spatial and temporal effects of wildfire on hydrology of a steep rangeland watershed. Measurement of infiltration and interrill erosion; Comparison of plot-scale spatial and temporal variability in fire impacts; Derivation of an index of water repellency; Comparison of cumulative erosion on burned and unburned coppices.

The U.S. Department of Agriculture, Agricultural Research Service, Northwest Watershed Research Center initiated a stream discharge and suspended-sediment research program at Reynolds Creek Experimental Watershed in the early 1960s. Continuous discharge measurements began at two sites in 1963, at three additional sites in 1964, and at eight additional sites in subsequent years. Contributing areas to these gauging stations range from 1.03 to >23,822 ha, selected to represent the broad range of environmental settings found across northwestern rangelands. Quality-controlled, validated breakpoint and hourly stream discharge data sets are available for these 13 sites for the period 1963 through 1996 (or for a subset of that time for some sites). Suspended-sediment data are available for three gauging stations (high elevation, middle elevation, and low elevation). All data are available on the Northwest Watershed Research Center anonymous ftp site (ftp.nwrc.ars.usda.gov). [ABSTRACT FROM AUTHOR]

BSTRACT: Soil infiltration capacity and interrill erosion are significantly influenced by soil frost on western rangelands which are characterized by cold winters and numerous freeze-thaw cycles. However, little is known about the variable influence of this phenomenon. Infiltration and interrill erosion were measured within a sagebrush-grass plant community during the winter, spring, and summer of 1989. Significant spatial and temporal differences in infiltration capacity and interrill erosion were found for shrub coppice dune and dune interspace soils. Infiltration was generally higher for coppice dune soils compared to interspace soils throughout the year. Infiltration capacity for both soils was lowest early in the year when the soil was frozen or saturated, then increased as the soil dried in the spring and summer. Interrill erosion was consistently lower for coppice dune soils compared to interspace soils. Erosion from interspace soils was greatest during a 19-day period in late winter characterized by diurnal freeze-thaw cycles, saturated surface soil conditions, and soil slaking. [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]