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This webinar discusses the benefits of altering timing of grazing to reduce annuals and maintain perennial bunchgrasses. It also discusses the detrimental impacts of repeated spring defoliation on perennials. Kirk Davies, Lead Rangeland Scientist with USDA ARS, presented.
This webinar was the third in our 2018 Webinar Series: Moving the Needle on Cheatgrass: Putting What We Know into Practice.
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Comparisons of observed and simulated historical area burned indicate simulated future fire vulnerability could be underestimated by 3% in the Sierra Nevada and overestimated by 3% in the Rocky Mountains. Projections show that water‐limited forests in the Rocky Mountains, Southwest, and Great Basin regions will be the most vulnerable to future drought‐related mortality, and vulnerability to future fire will be highest in the Sierra Nevada and portions of the Rocky Mountains. High carbon‐density forests in the Pacific coast and western Cascades regions are projected to be the least vulnerable to either drought or fire. Importantly, differences in climate projections lead to only 1% of the domain with conflicting low and high vulnerability to fire and no area with conflicting drought vulnerability. Our drought vulnerability metrics could be incorporated as probabilistic mortality rates in earth system models, enabling more robust estimates of the feedbacks between the land and atmosphere over the 21st century.
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This collection of essays—divided into three key categories: Risk, Culture, and Operations—daylights qualities and practices in the wildland fire service across a broad spectrum, from outdated and unwarranted to honorable and profound. We must acknowledge our current culture and its shortcomings while using its strengths to lead change.
Here, we ask how mean climate and climate variation at individual sites and across a species’ range affect the specialist-generalist spectrum of germination strategies exhibited by 10 arid land forbs. We investigated these relationships using climate data for the western United States, occurrence records from herbaria, and germination trials with field-collected seeds, and predicted that generalist strategies would be most common in species that experience a high degree of climate variation or occur over a wide range of conditions. We used two metrics to describe variation in germination strategies: (a) selectivity (did seeds require specific cues to germinate?) and (b) population-level variation (did populations differ in their responses to germination cues?) in germination displayed by each species. Species exhibited distinct germination strategies, with some species demonstrating as much among-population variation as we observed among species. Modeling efforts suggested that generalist strategies evolve in response to higher spatial variation in actual evapotranspiration at a local scale and in available water in the spring and annual precipitation at a range-wide scale. Describing the conditions that lead to variation in early life-history traits is important for understanding the evolution of diversity in natural systems, as well as the possible responses of individual species to global climate change.
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Most people, including many familiar with fire ecology and future climate, assume that the area burned by wildfire will increase in a warmer climate. This depends a lot on what kind of ecosystem we mean. In all ecosystems, fuels must be available to fire for fires to get very big, but the climate controls on those fuels vary widely with vegetation. In wetter forests, it takes an abnormally warm, dry year to make normally wet fuels available. But in many drier ecosystems, fuels are dry enough to burn most years—whether fires get big depends also on whether there is sufficient fuel available to carry fires over large areas. In this kind of vegetation, abnormally wet years in the year prior to fire can create larger or more connected fuels that then lead to larger fires. In this study, we use this concept to investigate how future area burned might be affected by climate change. We found that some ecosystems will burn much more, just as expected. But some will actually burn less. We characterized these futures for 70 different ecosystems around the West. The similarities and differences illustrate the range of futures that might be expected under climate change.
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Collectively, these studies show that the Weed-Suppressive Bacteria P. flourescens — strains ACK55, D7, and MB906 — are not likely to be effective in controlling invasive exotic grasses in western U.S. rangelands. There were no negative effects to exotic annual grasses, perennial bunchgrasses, or total community cover within three or four years of treatment when WSB was applied in the field alone or in combination with herbicides. It is possible that new formulations or application techniques could lead to more consistent, desired effects; however the studies described above tested three strains across a wide range of conditions, and yet no consistent effects were observed.
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This paper provides a historical perspective on fire in the Pacific Northwest. A warmer climate could bring more fire to the westside of the Cascade Range where summers are typically dry and will probably become drier. We can also expect longer fire seasons. The biggest concern for the future will be an increase in extreme weather events, which can lead to conditions that produce large and rapidly spreading wildfire.
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This study evaluates the implications of ten twenty-first century climate scenarios for snow, soil moisture, and fuel moisture across the conterminous western USA. A decline in mountain snowpack, an advance in the timing of spring melt, and a reduction in snow season are projected for five mountain ranges in the region. The accelerated depletion of mountain snowpack due to warming leads to reduced summer soil moisture across mountain environments. Similarly, warmer and drier summers lead to decreases of up to 25% in dead fuel moisture across all mountain ranges. Collective declines in spring mountain snowpack, summer soil moisture, and fuel moisture across western mountain ranges will increase fire potential in flammability-limited forested systems where fuels are not limiting.
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In this study, researchers determined vegetation response to fuel reduction by tree mastication (shredding) or seeding and then shredding by measuring cover of shrub and herbaceous functional groups on shredded and adjacent untreated areas on 44 sites in Utah. Findings suggested that shredding or seeding and then shredding should facilitate wildfire suppression, increase resistance to weed dominance, and lead toward greater resilience to disturbance by increasing perennial herbaceous cover.
View Chapter 11 of the book, Exotic brome-grasses in arid and semiarid ecosystems of the western US: causes, consequences, and management implications.
Human land uses are the primary cause of the introduction and spread of exotic annual Bromus species. Initial introductions were likely linked to contaminated seeds used by homesteading farmers in the late 1880s and early 1900s. Transportation routes aided their spread. Unrestricted livestock grazing from the 1800s through the mid-1900s reduced native plant competitors leaving large areas vulnerable to Bromus dominance. Ecosystems with cooler and moister soils tend to have greater potential to recover from disturbances (resilience) and to be more resistant to Bromus invasion and dominance. Warmer and drier ecosystems are less resistant to Bromus and are threatened by altered fire regimes which can lead to Bromus dominance, impacts to wildlife, and alternative stable states.