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Abstract Land managers across the western United States are faced with selecting and applying tree-removal treatments on pinyon (Pinus spp.) and juniper (Juniperus spp.) woodland-encroached sagebrush (Artemisia spp.) rangelands, but current understanding of long-term vegetation and hydrological responses of sagebrush sites to tree removal is inadequate for guiding management. This study applied a suite of vegetation and soil measures (0.5 − 990 m2), small-plot rainfall simulations (0.5 m2), and overland flow experiments (9 m2) to quantify the effects of mechanical tree removal (tree cutting and mastication) on vegetation, runoff, and erosion at two mid- to late-succession woodland-encroached sagebrush sites in the Great Basin, United States, 9 yr after treatment. Low amounts of hillslope-scale shrub (3 − 15%) and grass (7 − 12%) canopy cover and extensive intercanopy (area between tree canopies) bare ground (69 − 88% bare, 75% of area) in untreated areas at both sites facilitated high levels of runoff and sediment from high-intensity (102 mm • h− 1, 45 min) rainfall simulations in interspaces (~ 45 mm runoff, 59 − 381 g • m− 2 sediment) between trees and shrubs and from concentrated overland flow experiments (15, 30, and 45 L • min− 1, 8 min each) in the intercanopy (371 − 501 L runoff, 2 342 − 3 015 g sediment). Tree cutting increased hillslope-scale density of sagebrush by 5% and perennial grass cover by twofold at one site while tree cutting and mastication increased hillslope-scale sagebrush density by 36% and 16%, respectively, and perennial grass cover by threefold at a second more-degraded (initially more sparsely vegetated) site over nine growing seasons. Cover of cheatgrass (Bromus tectorum L.) was < 1% at the sites pretreatment and 1 − 7% 9 yr after treatment. Bare ground remained high across both sites 9 yr after tree removal and was reduced by treatments solely at the more degraded site. Increases in hillslope-scale vegetation following tree removal had limited impact on runoff and erosion for rainfall simulations and concentrated flow experiments at both sites due to persistent high bare ground. The one exception was reduced runoff and erosion within the cut treatments for intercanopy plots with cut-downed-trees. The cut-downed-trees provided ample litter cover and tree debris at the ground surface to reduce the amount and erosive energy of concentrated overland flow. Trends in hillslope-scale vegetation responses to tree removal in this study demonstrate the effectiveness of mechanical treatments to reestablish sagebrush steppe vegetation without increasing cheatgrass for mid- to late-succession woodland-encroached sites along the warm-dry to cool-moist soil temperature − moisture threshold in the Great Basin. Our results indicate improved hydrologic function through sagebrush steppe vegetation recruitment after mechanical tree removal on mid- to late-succession woodlands can require more than 9 yr. We anticipate intercanopy runoff and erosion rates will decrease over time at both sites as shrub and grass cover continue to increase, but follow-up tree removal will be needed to prevent pinyon and juniper recolonization. The low intercanopy runoff and erosion measured underneath isolated cut-downed-trees in this study clearly demonstrate that tree debris following mechanical treatments can effectively limit microsite-scale runoff and erosion over time where tree debris settles in good contact with the soil surface. [ABSTRACT FROM AUTHOR]

Western juniper ( Juniperus occidentalis Hook.) is a tree species occurring on 3.6 million ha in the northern Great Basin. This native species can be quite invasive, encroaching into sagebrush-grassland vegetation, forming woodlands, and dominating extensive landscapes. Control of encroaching juniper is often necessary and important. Efficacy of prescribed fire for western juniper control depends on many factors for which our understanding is still quite incomplete. This knowledge gap makes fire management planning for western juniper control more difficult and imprecise. Natural resource managers require a fire efficacy model that accurately predicts juniper mortality rates and is based entirely on predictors that are measurable prefire. We evaluated efficacy models using data from a fall prescribed fire conducted during 2002 in southwestern Idaho on mountain big sagebrush ( Artemisia tridentata Nutt. ssp. vaseyana [Rydb.] Beetle) rangelands with early to midsuccessional juniper encroachment. A logistic regression model, which included vegetation cover type, tree height, fire type, and bare ground as predictors, accurately predicted (area under the receiver operating characteristic [ROC] curve [AUC] = 0.881 ± 0.128 standard deviation [SD]) the mortality rate for a random sample of western juniper trees marked and assessed prefire and 5 yr post fire. Trees occurring in an antelope bitterbrush ( Purshia tridentata [Pursh] DC.) type, which had a heavy fuel load, were 8 times more likely to be killed by fire than trees in a mountain big sagebrush type, where loading was typically lighter. Probability of mortality decreased by 28.8% for each 1-meter increase in tree height. Trees exposed to head fire were 3 times as likely to be killed as those exposed to backing fire. Findings from this case study suggest that with just four factors which are readily quantifiable prefire, managers can accurately predict juniper mortality rate and thus make better informed decisions when planning prescribed fire treatments. [ABSTRACT FROM AUTHOR]

Elk ( Cervus elaphus L.) and cattle ( Bos taurus L.) co-occur on rangelands throughout western North America. Literature regarding range relations between elk and cattle, however, is contradictory, describing interspecific competition in some cases and complementary or facilitative relations in others. A better understanding of how sympatric elk and cattle behave at fine spatiotemporal scales is needed to properly allocate resources for these species. We used intensively sampled Global Positioning System (GPS) tracking data (1-sec intervals) to classify elk and cattle behavior and investigate their activity and movement strategies in the Blue Mountains of northeastern Oregon, United States, during summer and fall 2007. An ensemble classification approach was used to identify stationary, foraging, and walking behavior classes within the GPS datasets of mature beef and captive elk cows grazing in forested pastures during two randomized experiments, one in summer and the other fall. During summer, elk traveled farther per day, had larger walking budgets, exhibited more and longer walking bouts, and had higher walking velocities than beef cows. Cattle tended to emphasize intensive foraging over extensive movement and thus displayed larger foraging budgets and longer foraging bouts than elk. Site-by-species interactions, however, were detected for some foraging responses. During fall, when forage quality was limiting, elk exhibited a more foraging-centric mobility strategy while cattle emphasized an energy conservation strategy. These differing movement and energetic strategies tended to support the concept that elk and cattle occupy differing behavioral niches. Extensive foraging by elk and intensive foraging by cattle during summer correspond well with behaviors expected for elk searching out forbs in graminoid-dominated habitats and cattle foraging intensively on graminoids. Behaviors exhibited in the fall were consistent with elk continuing to exercise more selectivity among the available forage than cattle. These differing strategies, consequently, would moderate the potential for direct interspecific competition during summer and fall. [ABSTRACT FROM AUTHOR]

Increasing trends in wildfire activity on semi-arid rangelands necessitate advancement in understanding of fire impacts on vegetation, soils, and runoff and erosion processes. This study used artificially applied rainfall and concentrated overland flow experiments to evaluate the ecohydrologic response and recovery of a semi-arid shrubland in the Great Basin Region, USA, following fire. Rainfall experiments were conducted at the 0.5 m 2 plot scale to assess fire impacts on rainsplash and sheetflow processes. Concentrated flow experiments were applied on 9 m 2 plots to evaluate fire impacts on concentrated overland flow processes. Vegetation, soil, hydrologic, and erosion variables were assessed at each scale pre-fire and 1, 2, and 5 yr post-fire. Infiltration and runoff on rainfall simulation plots were affected more by measured background soil water repellency than fire effects on vegetation and soils. Runoff from rainfall on shrub-dominated plots was unchanged 1 yr post-fire, but runoff from interspace plots between shrubs declined 1 yr post-fire. Runoff increased on shrub and interspace rainfall plots 2 yr post-fire and then declined in the 5 yr post-fire. Bare ground generally declined across study years, implicating the temporal variability in soil water repellency as the causal factor for infiltration and runoff trends. Erosion on rainfall plots increased by factors of 8 to more than 10 following fire removal of vegetation and ground cover and declined with vegetation recovery through five growing seasons. Concentrated overland flow plots generated slightly more total runoff and 26-fold more total sediment 1 yr following burning relative to pre-fire measures. Erosion from concentrated overland flow remained greater on burned than unburned plots after five growing seasons even though ground cover returned to approximately 85%. The relative recovery of vegetation and total ground cover were typical for the shrubland community assessed, but elevated erosion with 85% ground cover 5 yr post-fire was unexpected. The persistent high sediment delivery from concentrated plots is attributed to the fine textured soils and thin litter accumulation. The importance of considering erodibility in context with sediment supply and vegetative recovery is discussed. The results demonstrate the complexity of post-fire ecohydrologic interactions, advance process understanding of post-fire ecohydrologic responses for semi-arid rangelands, and underscore the need for additional studies on post-fire recovery over time. [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]

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]

Bottlebrush squirreltail (Elymus elymoides) and big squirreltail (Elymus multisetus) have been identified as high-priority species for restoration and rehabilitation of millions of acres of rangeland in the western United States that have been degraded by wildfire and introduced annual weeds. In this study, squirreltail accessions from Idaho, Colorado, Utah, Arizona and New Mexico were grown in a nursery environment to produce seeds in two different years for germination evaluation at 11 constant temperatures. A statistical-gridding model was used to predict cumulative germination rate of each seedlot for eight simulated planting dates between 1 January and 28 May over a 38-year seedbed-microclimatic simulation. Predicted germination response under simulated conditions of field-variable temperatures yielded a broader ecological basis for the relative ranking of thermal response than was obtained from single-value germination indices derived from either constant-temperature experiments, or from analysis of thermal-time coefficients. [Copyright &y& Elsevier]

• 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]

Abstract: Cheatgrass (Bromus tectorum L.) has come to dominate millions of hectares of rangeland in the Intermountain western United States. Previous studies have hypothesized that one mechanism conferring a competitive advantage to this species is the ability to germinate rapidly at low temperatures in the fall, winter and spring and, therefore, initiate growth and establishment more rapidly than more desirable perennial bunchgrass species. In this experiment, we developed thermal-germination-response models for multiple seedlots of cheatgrass and five perennial grass species. We conducted sensitivity analysis on potential-cumulative-germination response to a 38-year simulation of field-variable conditions of seedbed temperature and moisture. Cheatgrass uniformly germinated at a higher rate, and required significantly less time to complete germination than any of the perennial species for all but the slowest seed subpopulations. A germination-rate-sum index was used to integrate relative response characteristics over time. This index showed that germination rate of the most rapidly germinating subpopulations of cheatgrass was 2–5 times higher than for the other species tested. Model simulations of this type provide a more ecologically relevant basis for seedlot evaluation as they allow comparisons across a wide range of potential conditions that may be experienced in the field. [Copyright &y& Elsevier]

• 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]