Fire Ecology & Effects
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The results of this study indicate that post-fire natural regeneration in the Blue Mountains over the last 20 years has generally been sufficient to maintain forest resilience. Recruitment differs dramatically, however, across sites. In burned areas with abundant surviving adult trees 100 m away or less and on north-facing slopes, hundreds or thousands of seedlings per hectare may establish within the first 10 to 15 years post-fire. In contrast, conifer densities in large high-severity burn patches (i.e., larger than 100 to 200 m in radius) with high overstory mortality, especially those on warmer sites, may be insufficient to meet local silvicultural guidelines or maintain forest ecosystem function without supplementary replanting. Some of these marginal sites may be susceptible to ecosystem state transitions to shrub or grasslands. The results of this study also suggest that as climate change causes temperatures to warm and increases the probability of growing season moisture deficits, Douglas-fir recruitment may decline in drought-prone sites. Ponderosa pine seedlings may be more resilient to warming conditions, though as warming continues they also will become vulnerable to drought stress.
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We did not detect a difference in mean pyrogenic carbon (PyC) concentration of the mineral soil between the spring burns and the unburned controls; however, the spring burn plots did contain a number of isolated pockets with very high concentrations of PyC, suggesting a patchier burn pattern for these plots. In general, there was no detectable difference in any of the response variables when comparing the various prescribed burn treatments to one another. Reestablishing fire in these forests resulted in minor effects on the PyC concentration and pH, which may have beneficial impacts on soil carbon and available nutrients, while having few effects on other soil characteristics. This suggests that the application of low severity prescribed fires should result in little detrimental change to soils of ponderosa pine forests of the Southern Blue Mountains, while achieving management objectives such as reduction of surface fuels.
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Over the last 30 years, in woodland and forested ecosystems across the southwestern US, there has been an increasing trend in fire activity. Altered land use practices and more recent changes in precipitation patterns and warmer temperatures are widely thought to contribute to departures in fire regimes toward more frequent and larger fires with more extreme fire behavior that threatens the persistence of the various forested ecosystems. We examined climate-fire relationships in these vegetation types in Arizona and New Mexico using an expanded satellite-derived burn severity dataset that incorporates over one million additional burned hectares analyzed as extended assessments to the MTBS project’s data and five climate variables from PRISM. Climate-fire relationships were identified by comparing annual total area burned, area burned at high/low severity, and percent high severity regionally with fire season (May-August) and water year (October-September) temperature, precipitation, and vapor pressure deficit (VPD) variables. The high severity indicators were also derived for each fire individually to see if climate-fire relationships persist at the scale of the individual fire. Increasing trends toward more arid conditions were observed in all but two of the climate variables. Furthermore, VPD-fire correlations were consistently as strong or more correlated compared to temperature or precipitation indicators alone, both regionally and at the scale of the individual fire. Thus, our results support the use of VPD as a more comprehensive climate metric than temperature or other water-balance measures to predict future fire activity. Managers will have to face the implications of increasing high severity fire as trends in climate toward warmer and drier conditions become an increasingly dominant factor in driving fire regimes towards longer and more intense fire seasons across the Southwest.
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Many studies have examined how fuels, topography, climate, and fire weather influence fire severity. Less is known about how different forest management practices influence fire severity in multi‐owner landscapes, despite costly and controversial suppression of wildfires that do not acknowledge ownership boundaries. In 2013, the Douglas Complex burned over 19,000 ha of Oregon & California Railroad (O&C) lands in Southwestern Oregon, USA. O&C lands are composed of a checkerboard of private industrial and federal forestland (Bureau of Land Management, BLM) with contrasting management objectives, providing a unique experimental landscape to understand how different management practices influence wildfire severity. Leveraging Landsat based estimates of fire severity (Relative differenced Normalized Burn Ratio, RdNBR) and geospatial data on fire progression, weather, topography, pre‐fire forest conditions, and land ownership, we asked (1) what is the relative importance of different variables driving fire severity, and (2) is intensive plantation forestry associated with higher fire severity?
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In ponderosa pine (Pinus ponderosa) forests of the western United States, prescribed burns are used to reduce fuel loads and restore historical fire regimes. The season of and interval between burns can have complex consequences for the ecosystem, including the production of pyrogenic carbon (PyC). PyC plays a crucial role in soil carbon cycling, displaying turnover times that are orders of magnitude longer than unburned organic matter. This work investigated how the season of and interval between prescribed burns affects soil organic matter, including the formation and retention of PyC, in a ponderosa pine forest of eastern Oregon.
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Scientists at the Southern Research Stations of the US Forest Service combined the hydrometeorological and fire data for 168 fire-affected areas in the contiguous United States collected between 1984 and 2013. This enabled them to determine when wildland fires can affect the annual amount of flow in rivers, and to create a suite of climate and wildland fire impact models adapted to local conditions.
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Today many forested landscapes in western states have a “fire debt.” Humans have prevented normal levels of fire from occurring, and the bill has come due. Increasingly severe weather conditions and longer fire seasons due to climate change are making fire management problems more pressing today than they were just a few decades ago. And the problem will only get worse.
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Although we detected shifts in the relative abundance of several bee and plant genera along the fire severity gradient, the two most abundant bee genera (Bombus and Halictus) responded positively to high fire severity despite differences in their typical foraging ranges. Our study demonstrates that within a large wildfire mosaic, severely burned forest contained the most diverse wild bee communities. This finding has particularly important implications for biodiversity in fire-prone areas given the expected expansion of wildfires in the coming decades.
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Taken together, findings suggest that the response of stream chemistry to wildfires in the Sierra Nevada, California, can persist for years, varying with both fire severity and site-specific characteristics. These impacts may have important implications for biogeochemical cycles and productivity in aquatic ecosystems in fire-adapted landscapes.
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Strategically placed landscape area fuel treatments in the Sierra Nevada were put to the test in this study when the American Fire burned through previously treated areas. Both fire effects and initial post-fire conifer regeneration were investigated.