Research and Publications
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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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We have been studying the WUI in the U.S. for more than 10 years, looking at where WUI areas were once located, where they are now, and where we expect them to be in the coming decades. Our new data set provides the first high-resolution data on WUI change from 1990 to 2010, revealing how housing growth and wildland vegetation have combined over time. We developed new algorithms that converted the decennial Census standalone data into a consistent dataset on housing growth across the conterminous U.S.
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This report synthesized insights from current understanding of drought impacts at stand-to-biogeographic scales, including management options, and we identify challenges to be addressed with new research. Large stand-level shifts underway in western forests already are showing the importance of interactions involving drought, insects, and fire. Diebacks, changes in composition and structure, and shifting range limits are widely observed. Throughout the continental United States, the combination of projected large climate-induced shifts in suitable habitat from modeling studies and limited potential for the rapid migration of tree populations suggests that changing tree and forest biogeography could substantially lag habitat shifts already underway. Forest management practices can partially ameliorate drought impacts through reductions in stand density, selection of drought-tolerant species and genotypes, artificial regeneration, and the development of multistructured stands. However, silvicultural treatments also could exacerbate drought impacts unless implemented with careful attention to site and stand characteristics. Gaps in our understanding should motivate new research on the effects of interactions involving climate and other species at the stand scale and how interactions and multiple responses are represented in models. This assessment indicates that, without a stronger empirical basis for drought impacts at the stand scale, more complex models may provide limited guidance.
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View Volume 2
Fifty years ago, riparian habitats were not recognized for their extensive and critical contributions to wildlife and the ecosystem function of watersheds. This changed as riparian values were identified and documented, and the science of riparian ecology developed steadily. Papers in this volume range from the more mesic northwestern United States to the arid Southwest and Mexico. More than two dozen authors – most with decades of experience – review the origins of riparian science in the western United States, document what is currently known about riparian ecosystems, and project future needs. Topics are widespread and include: interactions with fire, climate change, and declining water; impacts from exotic species; unintended consequences of biological control; the role of small mammals; watershed response to beavers; watershed and riparian changes; changes below large dams; water birds of the Colorado River Delta; and terrestrial vertebrates of mesquite bosques. Appendices and references chronicle the field’s literature, authors, “riparian pioneers,” and conferences.
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This study found substantial evidence for the ability of all markers to reduce collisions (~ 57% reduction), with little difference between the tested marker types. It found strong evidence for lower collision probabilities at fences with wood posts and on fences farther from leks. Results also indicated a negative relationship between collision probabilities and the difference between fence and vegetation heights. There was little evidence for differences in collision risk between areas defined as “high” or “moderate” risk in a pre-existing collision risk map. Findings recommend integrating fence marking into conservation practices requiring fencing, and prioritizing fence marking near leks in areas with greater fence exposure.
A proposed mechanism for high pathogen-caused mortality in the seed bank of an invasive annual grass
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Pyrenophora semeniperda can infect nondormant Bromus tectorum seeds under optimal germination conditions, but most escape mortality. This reduces pathogen fitness relative to infection of dormant seeds, which are almost always killed. However, field experiments showed that a large proportion of seeds killed following inoculum addition were not accounted for as dormant seeds, but instead were likely nondormant seeds that would have germinated without inoculum addition. We hypothesized that widely fluctuating water availability to seeds would favor pathogenesis by delaying germination and allowing disease progression at water potentials below those that permit radicle emergence. With dehydration at -4 MPa, mortality increased with dehydration duration after short or long imbibition. At -40MPa, mortality increased with dehydration duration only after long imbibition. At -150MPa, there was no effect of dehydration duration on generally low mortality. These results illustrate that fluctuating moisture can cause high nondormant seed mortality, explaining how this pathogen kills nondormant seeds.
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This study identified contrasting climate niches for ten Great Basin understorey forbs, including differences in both mean values and climate variability. These estimates can guide species selection for restoration by identifying species with a high tolerance for climate variability and large climatic niches. They can also help conservationists to understand which species may be least tolerant of climate variability, and potentially most vulnerable to climate change
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A study comparing insect communities in grazed, rested, and idled pastures in Montana found that the types of insects that provide a critical food source for sage grouse chicks and other shrub- and grassland-dependent birds were 13 percent more prevalent on managed versus idled rangelands.
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Key findings of this research were:
- Burned low-elevation sagebrush sites can be seeded with mixes of native grasses, forbs and shrubs using rangeland drills adapted for seeding large and small seeds in separate rows.
- Seeding technique, timing of seed application, and seeding rate are important considerations when seeding Wyoming big sagebrush.
- The best techniques for establishing Wyoming big sagebrush are seeding at high rates via a drill in late fall.
- Success of seeding treatments on semiarid sites is ultimately dependent on weather conditions and competitive pressure from invasive weeds, and it may be best to delay treatments until conditions are predicted to be favorable, depending on the feasibility of weed control at the site.
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This study investigated how grazing affected plant communities in terms of cover and richness of native and invasive species and how topographic sites of summit, backslope and toeslope altered these relationships. The plant communities were affected by the independent effects of grazing, site and year. Across years, native cover was 39% greater in grazed plots compared with ungrazed plots. Native species richness was slightly lower in ungrazed compared with grazed plots for toeslope sites relative to the other topographic positions. Invasive species cover was 17% lower in grazed plots compared with ungrazed plots and no predictors were found to contribute to significant differences across plots. Although we generally did not find expected relationships between site and plant response to grazing, this work demonstrates how managers can use livestock to quickly modify plant communities in areas with a long history of grazing absence.