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The relationship between traffic and forest road erosion has been studied for decades, and the answer to the question 'what happens when traffic is present on unpaved forest roads?' is simple: erosion increases. However, the answer to the question 'why does it increase?' is complex and requires us to consider forest road erosion through an integrated lens. Fully understanding how traffic affects forest road erosion will allow us to control forest road erosion effectively. In this synthesis, we look at forest road erosion literature and focus the discussion on the interactions between traffic and erosion. Specifically, we explore four main hypotheses that have been proposed to explain how traffic affects erosion. These hypotheses are discussed in detail, including what data and information are required to evaluate them. In addition to the specific traffic-erosion interactions, we review important factors that interact with traffic to enhance erosion. Finally, we propose a framework that describes forest road erosion as a combination of all limiting factors. This framework can help guide future data collection needs, allow us to form a more holistic understanding of forest road erosion, and ultimately improve predictions of erosion from forest roads. Key words: Resource roads, erosion, traffic, sediment, rut, runoff, 1. Introduction Erosion from forest roads is a long-standing environmental problem (e.g., Trimble and Sartz 1957; Trimble 1959; Packer 1967; Kochenderfer 1970; Megahan and Kidd 1972; Bilby, Sullivan and Duncan [...]

Increases in burned area and large fire occurrence are widely documented over the western United States over the past half century. Here, we focus on the elevational distribution of forest fires in mountainous ecoregions of the western United States and show the largest increase rates in burned area above 2,500 m during 1984 to 2017. Furthermore, we show that high-elevation fires advanced upslope with a median cumulative change of 252 m (-107 to 656 m; 95% CI) in 34 y across studied ecoregions. We also document a strong interannual relationship between high-elevation fires and warm season vapor pressure deficit (VPD). The upslope advance of fires is consistent with observed warming reflected by a median upslope drift of VPD isolines of 295 m (59 to 704 m; 95% CI) during 1984 to 2017. These findings allow us to estimate that recent climate trends reduced the high-elevation flammability barrier and enabled fires in an additional 11% of western forests. Limited influences of fire management practices and longer fire-return intervals in these montane mesic systems suggest these changes are largely a byproduct of climate warming. Further weakening in the high-elevation flammability barrier with continued warming has the potential to transform montane fire regimes with numerous implications for ecosystems and watersheds.

Wildfires have short- and long-term impacts on the geoenvironment, including the changes to biogeochemical and mechanical properties of soils, landfill stability, surface- and groundwater, air pollution, and vegetation. Climate change has increased the extent and severity of wildfires across the world. Simultaneously, anthropogenic activities—through the expansion of urban areas into wildlands, abandonment of rural practices, and accidental or intentional fire-inception activities—are also responsible for a majority of fires. This paper provides an overall review and critical appraisal of existing knowledge about processes induced by wildfires and their impact on the geoenvironment. Burning of vegetation leads to loss of root reinforcement and changes in soil hydromechanical properties. Also, depending on the fire temperature, soil can be rendered hydrophobic or hydrophilic and compromise soil nutrition levels, hinder revegetation, and, in turn, increase post-fire erosion and the debris flow susceptibility of hillslopes. In addition to direct hazards, wildfires pollute air and soil with smoke and fire suppression agents releasing toxic, persistent, and relatively mobile contaminants into the geoenvironment. Nevertheless, the mitigation of wildfires' geoenvironmental impacts does not fit within the scope of this paper. In the end, and in no exhaustive way, some of the areas requiring future research are highlighted. [ABSTRACT FROM AUTHOR]

Forest roadside ditch lines capture and redirect road runoff and typically have erosion control treatments installed therein. Existing methods used to determine the effectiveness of roadside ditch line erosion control treatments estimate fixed fractional reductions in sediment yield. However, fixed fractional reductions do not describe dependence on any measurable physical property of treatment, climate, and the environment. Here, we use additional flow roughness induced by erosion control treatments as a metric that can be used as the basis of estimating treatment effectiveness in varying contexts. We investigate its utility in small‐scale field experiments in western Washington. We measured the physical characteristics of each ditch (e.g., shape, soil texture, and slope) and flow velocities and sediment concentrations for each treatment under multiple experimental discharges. We then used the concept of shear stress partitioning to relate sediment yield from the ditch line erosion treatments to grain shear stress, which is a function of flow roughness (Manning's n) of the respective treatment. We found that (1) a given erosion control treatment produced consistent Manning's n values across multiple replications and sites, with a bare ditch (no treatment) yielding the lowest roughness (n = 0.05) and a densely wattled ditch yielding the highest roughness (n = 0.75); (2) sediment load and calculated grain shear stress data yielded a single positive relationship when data from each experiment were combined, which suggests the effect of additional roughness on grain shear stress is a main driver in the reduction of ditch line sediment load; and (3) in our dataset, fractional erosion reduction had a variable and nonlinear sensitivity to low flow rates (99% of observed flows) for lower roughnesses. Our results demonstrate how additional flow roughness can be used as a general metric to help evaluate the effectiveness of ditch line erosion control treatments for a variety of physical conditions. [ABSTRACT FROM AUTHOR]

Wildland road removal is a common practice across the U.S. and in some parts of Canada. The main types of road removal include ripping, stream crossing restoration, and full recontour. Road removal creates a short-term disturbance that may temporarily increase sediment loss. However, research and long-term monitoring have shown that road removal both reduces erosion rates and the risk of road-induced landslides. Research is needed to determine whether road removal is effective at restoring ecosystem processes and wildlife habitat. We propose several research questions and the types of studies needed to further road removal efforts. With greater understanding of the impacts of road removal, land managers can more effectively prioritize which roads to leave open and which roads to consider for future road removal projects.

Recent and projected climate warming trends have prompted interest in impacts on coldwater fishes. We examined the role of climate (temperature and flow regime) relative to geomorphology and land use in determining the observed distributions of three trout species in the interior Columbia River Basin, USA. We considered two native species, cutthroat trout (Oncorhynchus clarkii) and bull trout (Salvelinus confluentus), as well as nonnative brook trout (Salvelinus fontinalis). We also examined the response of the native species to the presence of brook trout. Analyses were conducted using multilevel logistic regression applied to a geographically broad database of 4165 fish surveys. The results indicated that bull trout distributions were strongly related to climatic factors, and more weakly related to the presence of brook trout and geomorphic variables. Cutthroat trout distributions were weakly related to climate but strongly related to the presence of brook trout. Brook trout distributions were related to both climate and geomorphic variables, including proximity to unconfined valley bottoms. We conclude that brook trout and bull trout are likely to be adversely affected by climate warming, whereas cutthroat trout may be less sensitive. The results illustrate the importance of considering species interactions and flow regime alongside temperature in understanding climate effects on fish. Les tendances recentes et prevues de rechauffement du climat ont suscite de l'interet pour les impacts sur les poissons d'eau froide. Nous examinons le role du climat (temperature et regime hydraulique) en fonction de la geomorphologie et de l'utilisation des terres dans la determination de la repartition observee chez trois especes de <> dans le bassin versant interieur du Columbia, E.-U. Nous observons deux especes indigenes, la truite fardee (Oncorhynchus clarkii)et l'omble a tete plate (Salvelinus confluentus), ainsi que l'omble de fontaine (Salvelinus fontinalis) non indigene. Nous etudions aussi la reaction des especes indigenes a la presence de l'omble de fontaine. Les analyses consistent en des regressions logistiques a niveaux multiples sur une base de donnees de grande envergure geographique de 4165 inventaires de poissons. Les resultats indiquent que les repartitions des ombles a tete plate sont fortement reliees aux facteurs climatiques et moins fortement correlees a la presence d'ombles de fontaine et aux variables geomorphologiques. Les repartitions des truites fardees sont faiblement reliees au climat, mais fortement reliees a la presence de l'omble de fontaine. Les repartitions des ombles de fontaine sont reliees a la fois au climat et aux variables geomorphologiques, en particulier la proximite des fonds de vallees elargis. Nous concluons que l'omble de fontaine et l'omble a tete plate seront vraisemblablement affectes negativement par le rechauffement climatique, alors que la truite fardee sera peut-etre moins sensible. Nos resultats soulignent l'importance de considerer les interactions entre les especes et le regime hydraulique en plus de la temperature pour comprendre les effets du climat sur les poissons. [Traduit par la Redaction], Introduction Recent warming trends and projections of future climate change have prompted interest in the climate sensitivity of aquatic organisms (Parmesan 2006; Battin et al. 2007; McCullough et al. 2009). [...]

Collectively, these included 84 streams, where LCT had been observed by management agencies (occupied streams) and 127 historical streams, where LCT had not been observed in the last several decades (unoccupied streams). Unoccupied streams were assumed to contain LCT habitat because they currently support non-native trout populations (the likely cause of LCT extirpation) or were selected by management partners based on habitat data or resolved historical threats. In streams where LCT co-occurred with non-native trout, we simulated effects of non-native trout eradication by comparing LCT population forecasts with and without non-natives. Eliminating non-natives while simultaneously reducing environmental stochasticity (to the mean for populations without non-native trout or 73% of the mean for populations with non-native trout) substantially reduced extinction risks for most populations, where non-native trout co-occurred with LCT (Fig.). [Extracted from the article]