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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]

Hydrologic response to rainfall on fragmented or burnt hillslopes is strongly influenced by the ensuing connectivity of runoff and erosion processes. Yet cross-scale process connectivity is seldom evaluated in field studies owing to scale limitations in experimental design. This study quantified surface susceptibility and hydrologic response across point to hillslope scales at two degraded unburnt and burnt woodland sites using rainfall simulation and hydrologic modelling. High runoff (31-47 mm) and erosion (154-1893 g m-2) measured at the patch scale (13 m²) were associated with accumulation of fine-scale (0.5-m²) splash-sheet runoff and sediment and concentrated flow formation through contiguous bare zones (64-85% bare ground). Burning increased the continuity of runoff and sediment availability and yield. Cumulative runoff was consistent across plot scales whereas erosion increased with increasing plot area due to enhanced sediment detachment and transport. Modelled hillslope-scale runoff and erosion reflected measured patch-scale trends and the connectivity of processes and sediment availability. The cross-scale experiments and model predictions indicate the magnitude of hillslope response is governed by rainfall input and connectivity of surface susceptibility, sediment availability, and runoff and erosion processes. The results demonstrate the importance in considering cross-scale structural and functional connectivity when forecasting hydrologic and erosion responses to disturbances. [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]

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.

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]

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]

Runoff and erosion estimates are needed for rangeland management decisions and evaluation of ecosystem services derived from rangeland conservation practices. The information on the effect of scale on runoff and erosion and on the choice of runoff and erosion predictors remains scarce. The objective of this work was to evaluate the effect of scale on the selection of runoff and erosion predictors with the data from rich National Range Study database containing data from 444 coupled large (3.05 m by 9.1 m) and small (0.61 m by 1.22 m) plot field experiments. With data from both plot sizes, we assessed the usefulness of adding site-specific soil surface information to basic soil and rainfall data in order to estimate runoff and erosion in rangelands. We observed the scale-dependence of the runoff coefficient and the sediment yield. Smaller values of both variables were found at large plots as compared to small plots. Regression trees were used to build predictive relationships and evaluate the relative importance of predictors. Rainfall and basic soil properties were identified as the major predictors of runoff coefficients and sediment yields at both scales. Differences in the importance of predictors were observed between the two plot sizes and between predictions of runoff and sediment yield at the same plot sizes. The antecedent soil water content was not as important as rainfall parameters. Overall, including site-specific soil surface properties did not improve the predictability of the runoff coefficient and the sediment yield. The difference in runoff and sediment yield between small and large plots was found most likely because the small plots only contained a single soil/vegetation expression, whereas there was a matrix of vegetation clumps and bare interspaces arranged in a non-uniform pattern at the large plots. The variability of runoff and sediment yield may depend on how the latter pattern expresses itself in each of the large plots. More research or a different approach is required to account for vegetation-driven spatial hydrologic processes and their influence on rangeland runoff and soil erosion processes. [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]

• Rock cover, surface physical and hydraulic roughness increased as rainfall progressed. • Steeper slopes developed greater surface physical and hydraulic roughness. • Final soil loss rates decreased to a relative similar value across three slope gradients. • Erosion rates evolved toward being less sensitive to slope gradient than they would otherwise be. • Flow velocity and effective shear stress were appropriate predictors for soil loss. The dynamic interaction between erosion, surface morphology and flow hydraulics, causes steeper slopes to develop greater physical and hydraulic roughness, such that the slope can evolve toward a state of equilibrium wherein runoff velocity is independent of slope gradient. This study tests, under controlled condition, the hypothesis that erosion rate may also evolve toward a state wherein erosion rate is uniform across slope gradients after slope-velocity-equilibrium is established. A series of rainfall simulations (intensities of 59 and 178 mm hr−1) were conducted on 2 m by 6.1 m stony soil plot under three slope treatments (5%, 12% and 20%, replicated) with surface elevation, rock cover, flow velocity and sediment measurements. The results showed: 1) rock cover, and both surface physical (random roughness) and hydraulic roughness (Darcy–Weisbach friction) increased as rainfall progressed, leading to reductions in flow velocities and soil loss rates; 2) steeper slopes developed greater surface physical and hydraulic roughness; 3) the final soil loss rates ranged from 0.87 to 1.28 g min−1 m−2, and from 5.36 to 16.01 g min−1 m−2, which were approximately 6% to 15% of the initial maximum values, under low and high rainfall intensity, respectively; 4) soil loss rate was inversely correlated with rock cover while exhibiting no correlation with the random roughness index; 5) the linear coefficient of slope gradient relative to erosion rate measured on the most evolved surface were only 6.5% and 7.3% of those on initial surfaces under low and high rainfall intensity, respectively, implying that erosion rate evolved toward being less sensitive to slope gradient than it would otherwise be; 6) flow velocity and effective shear stress were found to be appropriate predictors for soil loss rate. This study supports the hypothesis of erosion equilibrium, implying that erosion rate decreases as a function of erosion pavement and that influence of slope gradient on soil erosion declines due to the dynamic interactions between soil erosion, surface morphology, and flow hydraulics. [ABSTRACT FROM AUTHOR]