Hydrologic and Erosion Responses to Wildfire Along the Rangeland-Xeric Forest Continuum in the Western US: A Review and Model of Hydrologic Vulnerability

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

Short-Term Effects of Tree Removal on Infiltration, Runoff, and Erosion in Woodland-Encroached Sagebrush Steppe

Land owners and managers across the western United States are increasingly searching for methods to evaluate and mitigate the effects of woodland encroachment on sagebrush steppe ecosystems. We used small-plot scale (0.5 m2) rainfall simulations and measures of vegetation, ground cover, and soils to investigate woodland response to tree removal (prescribed fire and mastication) at two late-succession woodlands. We also evaluated the effects of burning on soil water repellency and effectiveness of aggregate stability indices to detect changes in erosion potential. Plots were located in interspaces between tree and shrub canopies and on undercanopy tree and shrub microsites. Erosion from untreated interspaces in the two woodlands differed more than 6-fold, and erosion responses to prescribed burning differed by woodland site. High-intensity rainfall (102 mm · h-1) on the less erodible woodland generated amplified runoff and erosion from tree microsites postfire, but erosion (45–75 g · m-2) was minor relative to the 3–13-fold fire-induced increase in erosion on tree microsites at the highly erodible site (240–295 g · m-2). Burning the highly erodible woodland also generated a 7-fold increase in erosion from shrub microsites (220–230 g · m-2) and 280–350 g · m-2 erosion from interspaces. High levels of runoff (40–45 mm) and soil erosion (230–275 g · m-2) on unburned interspaces at the more erodible site were reduced 4–5-fold (10 mm and 50 g · m-2) by masticated tree material. The results demonstrate that similarly degraded conditions at woodland-encroached sites may elicit differing hydrologic and erosion responses to treatment and that treatment decisions should consider inherent site-specific erodibility when evaluating tree-removal alternatives. Strong soil water repellency was detected from 0 cm to 3 cm soil depth underneath unburned tree canopies at both woodlands and its strength was not altered by burning. However, fire removal of litter exacerbated repellency effects on infiltration, runoff generation, and erosion. The aggregate stability index method detected differences in relative soil stability between areas underneath trees and in the intercanopy at both sites, but failed to provide any indication of between-site differences in erodibility or the effects of burning on soil erosion potential

Revisiting the neuropathology of sudden infant death syndrome (SIDS)

Background: Sudden infant death syndrome (SIDS) is one of the leading causes of infant mortality in the United States (US). The extent to which SIDS manifests with an underlying neuropathological mechanism is highly controversial. SIDS correlates with markers of poor prenatal and postnatal care, generally rooted in the lack of access and quality of healthcare endemic to select racial and ethnic groups, and thus can be viewed in the context of health disparities. However, some evidence suggests that at least a subset of SIDS cases may result from a neuropathological mechanism. To explain these issues, a triple-risk hypothesis has been proposed, whereby an underlying biological abnormality in an infant facing an extrinsic risk during a critical developmental period SIDS is hypothesized to occur. Each SIDS decedent is thus thought to have a unique combination of these risk factors leading to their death. This article reviews the neuropathological literature of SIDS and uses machine learning tools to identify distinct subtypes of SIDS decedents based on epidemiological data. Methods: We analyzed US Period Linked Birth/Infant Mortality Files from 1990 to 2017 (excluding 1992–1994). Using t-SNE, an unsupervised machine learning dimensionality reduction algorithm, we identified clusters of SIDS decedents. Following identification of these groups, we identified changes in the rates of SIDS at the state level and across three countries. Results: Through t-SNE and distance based statistical analysis, we identified three groups of SIDS decedents, each with a unique peak age of death. Within the US, SIDS is geographically heterogeneous. Following this, we found low birth weight and normal birth weight SIDS rates have not been equally impacted by implementation of clinical guidelines. We show that across countries with different levels of cultural heterogeneity, reduction in SIDS rates has also been distinct between decedents with low vs. normal birth weight. Conclusions: Different epidemiological and extrinsic risk factors exist based on the three unique SIDS groups we identified with t-SNE and distance based statistical measurements. Clinical guidelines have not equally impacted the groups, and normal birth weight infants comprise more of the cases of SIDS even though low birth weight infants have a higher SIDS rate.Fil: Blackburn, Jessica. The Ohio State University College Of Medicine; Estados UnidosFil: Chapur, Valeria Fernanda. Universidad Nacional de Jujuy. Instituto de Ecorregiones Andinas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Ecorregiones Andinas; Argentina. Universidad Nacional de Jujuy. Instituto de Biología de la Altura; ArgentinaFil: Stephens, Julie A.. The Ohio State University College Of Medicine; Estados UnidosFil: Zhao, Jing. The Ohio State University College Of Medicine; Estados UnidosFil: Shepler, Anne. The Ohio State University College Of Medicine; Estados UnidosFil: Pierson, Christopher R.. The Ohio State University College Of Medicine; Estados UnidosFil: Otero, José Javier. The Ohio State University College Of Medicine; Estados Unido

Structural and Functional Connectivity as a Driver of Hillslope Erosion Following Disturbance

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

Effectiveness of Prescribed Fire to Re-Establish Sagebrush Steppe Vegetation and Ecohydrologic Function on Woodland-Encroached Sagebrush Reangelands, Great Basin, USA: Part II: Runoff and Sediment Transport at the Patch Scale

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

Effectiveness of Prescribed Fire to Re-Establish Sagebrush Steppe Vegetation and Ecohydrologic Function on Woodland-Encroached Sagebrush Rangelands, Great Basin, USA: Part I: Vegetation, Hydrology, and Erosion Responses

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 \u3e5-fold, on average, across both sites over nine growing seasons. Burning reduced low pre-fire sagebrush canopy cover (30 yr. Enhanced herbaceous cover in interspaces post-fire reduced runoff and sediment yield from high intensity rainfall simulations by \u3e2-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 fro

Hydrologic and Erosion Responses of Sagebrush Steppe Following Juniper Encroachment, Wildfire, and Tree Cutting

Extensive woodland expansion in the Great Basin has generated concern regarding ecological impacts of tree encroachment on sagebrush rangelands and strategies for restoring sagebrush steppe. This study used rainfall (0.5 m2 and 13 m2 scales) and concentrated flow simulations and measures of vegetation, ground cover, and soils to investigate hydrologic and erosion impacts of western juniper (Juniperus occidentalis Hook.) encroachment into sagebrush steppe and to evaluate short-term effects of burning and tree cutting on runoff and erosion responses. The overall effects of tree encroachment were a reduction in understory vegetation and formation of highly erodible, bare intercanopy between trees. Runoff and erosion from high-intensity rainfall (102 mm · h‒1, 13 m2 plots) were generally low from unburned areas underneath tree canopies (13 mm and 48 g · m‒2) and were higher from the unburned intercanopy (43 mm and 272 g · m‒2). Intercanopy erosion increased linearly with runoff and exponentially where bare ground exceeded 60%. Erosion from simulated concentrated flow was 15- to 25-fold greater from the unburned intercanopy than unburned tree canopy areas. Severe burning amplified erosion from tree canopy plots by a factor of 20 but had a favorable effect on concentrated flow erosion from the intercanopy. Two years postfire, erosion remained 20-fold greater on burned than unburned tree plots, but concentrated flow erosion from the intercanopy (76% of study area) was reduced by herbaceous recruitment. The results indicate burning may amplify runoff and erosion immediately postfire. However, we infer burning that sustains residual understory cover and stimulates vegetation productivity may provide long-term reduction of soil loss relative to woodland persistence. Simply placing cut-downed trees into the unburned intercanopy had minimal immediate impact on infiltration and soil loss. Results suggest cut-tree treatments should focus on establishing tree debris contact with the soil surface if treatments are expected to reduce short-term soil loss during the postcut understory recruitment period

Vegetation, Hydrologic, and Erosion Responses of Sagebrush Steppe 9 Yr Following Mechanical Tree Removal

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 \u3c 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

Bioactivity and structural properties of chimeric analogs of the starfish SALMFamide neuropeptides S1 and S2

The starfish SALMFamide neuropeptides S1 (GFNSALMFamide) and S2 (SGPYSFNSGLTFamide) are the prototypical members of a family of neuropeptides that act as muscle relaxants in echinoderms. Comparison of the bioactivity of S1 and S2 as muscle relaxants has revealed that S2 is ten times more potent than S1. Here we investigated a structural basis for this difference in potency by comparing the bioactivity and solution conformations (using NMR and CD spectroscopy) of S1 and S2 with three chimeric analogs of these peptides. A peptide comprising S1 with the addition of S2's N-terminal tetrapeptide (Long S1 or LS1; SGPYGFNSALMFamide) was not significantly different to S1 in its bioactivity and did not exhibit concentration-dependent structuring seen with S2. An analog of S1with its penultimate residue substituted from S2 (S1(T); GFNSALTFamide) exhibited S1-like bioactivity and structure. However, an analog of S2 with its penultimate residue substituted from S1 (S2(M); SGPYSFNSGLMFamide) exhibited loss of S2-type bioactivity and structural properties. Collectively, our data indicate that the C-terminal regions of S1 and S2 are the key determinants of their differing bioactivity. However, the N-terminal region of S2 may influence its bioactivity by conferring structural stability in solution. Thus, analysis of chimeric SALMFamides has revealed how neuropeptide bioactivity is determined by a complex interplay of sequence and conformation

Risk Assessment of Erosion from Concentrated Flow on Rangelands Using Overland Flow Distribution and Shear Stress Partitioning

Erosion rates of overland flow on rangelands tend to be relatively low, but under certain conditions where flow is concentrated, soil loss can be significant. Therefore, a rangeland site can be highly vulnerable to soil erosion where overland flow is likely to concentrate and exert high shear stress on soil grains. This concept is commonly applied in cropland and wildland soil erosion modeling using predictions of flow effective shear stress (shear stress applied on soil grains). However, historical approaches to partition shear stress in erosion models are computationally complex and require extensive parameterization. Furthermore, most models are not capable of predicting the conditions in which concentrated flow occurs on rangelands. In this study, we investigated the rangelands conditions at which overland flow is more likely to become concentrated and developed equations for partitioning the shear stress of concentrated flow on rangelands. A logistic equation was developed to estimate the probability of overland flow to become concentrated. Total shear stress of rangeland overland flow was partitioned into components exerted on soil, vegetation, and rock cover using field experimental data. In addition, we investigated the vegetation cover limit at which the effective shear stress component is substantially reduced, limiting the erosion rate. The results from the partitioning equations show that shear stress exerted on soil grains was relatively small in sheet flow. Shear stress exerted on soil grains in concentrated flow was significantly higher when bare soil exceeded 60% of the total surface area but decreased significantly when the bare soil area was less than 25% or when the plant base cover exceeded 20%. These percentages could be used as relative measures of hydrologic recovery for disturbed rangelands or as triggers that indicate a site is crossing a threshold beyond which soil erosion might accelerate due to the high effective shear stress