Post-fire Environment & Management
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Across the entire arthropod community, fire also had variable effects on community diversity. Fire tended to have a negative effect size on arthropods across life stages, but responses did vary among groups. Nearly all functional groups exhibited a negative response to fire with the exception of herbivores, for which abundance, diversity and richness increased after fire.
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No combinations of salvage intensity and distribution from among the scenarios we explored were able to fully mitigate the negative effect on the bird community; however, the magnitude of declines in abundance and diversity was smaller than expected, and the majority of the species analyzed had a non-significant response. We recommend targeting salvage activities in the Sierra Nevada to those locations where snags pose a safety issue or where reforestation is most needed to conserve this fire-adapted bird community.
Webinar recording.
Ecosystems of the western United States are experiencing vegetation type conversions (VTC) in response to land-use change, climate warming, and their interactive effects with wildland fire. VTC is one of the most pressing management issues in the southwestern US, yet current strategies to intervene and address change often use trial-and-error approaches devised after the fact. This presentation discusses findings on VTC challenges, management responses, and outcomes from the collective experience of managers, scientists, and practitioners across the southwestern US.
Ecological reorganization across the region is not only extensive – it is complex, predominantly driven by high-severity wildfire. By a large margin, affected semi-arid forests convert to shrubland, while chaparral and sagebrush areas nearly always convert to non-native grasses. Management interventions in VTC areas most often attempt to reverse changes, although these efforts cover only a small portion of high-severity burn areas undergoing VTC. Efforts to facilitate VTC are rare but hold the potential to cover large spatial areas.
The presenter’s findings underscore that type conversion is a common outcome of high-severity wildland fire in the southwestern US. As the drivers increase with climate change, VTC appears increasingly likely in many ecological contexts, and may require management paradigms to transition as well.
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To examine the short-term effects of wildfire on belowground processes in the northern Sierra Nevada, we collected soil samples along a gradient from unburned to high fire severity over 10 months following a wildfire. This included immediate pre- and post-fire sampling for many variables at most sites. While season and soil moisture did not substantially alter pH, microbial biomass, net N mineralization, and nitrification in unburned locations, they interacted with burn severity in complex ways to constrain N cycling after fire. In areas that burned, pH increased (at least initially) after fire, and there were non-monotonic changes in microbial biomass. Net N mineralization also had variable responses to wetting in burned locations. These changes suggest burn severity and precipitation patterns can interact to alter N cycling rates following fire.
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We evaluated seeding bitterbrush (Purshia tridentata) after wildfire in former western juniper (Juniperus occidentalis ssp. occidentalis) canopy compared with interspace microsites at six locations for 3 yr post seeding. Bitterbrush abundance was 3.6-fold greater in former canopy compared with interspace microsites after 3 yr. Bitterbrush height was 1.5 to 2.5-fold greater in former canopy compared with interspace microsites. The first year after fire, exotic annual grass cover was 15.6-fold greater in interspace compared with canopy microsites. Abundance and cover of other herbaceous vegetation were generally also greater in the interspace. Exotic annual grass and native bunchgrass abundance increased substantially over time in former canopy microsites, suggesting abundant resource availability. Less herbaceous competition and presumably greater resource availability in former canopies probably resulted in greater success of seeded bitterbrush. These results suggest that capitalizing on spatial variability in environments can be used to increase restoration efficiency. After fire in western juniper−encroached rangelands, former juniper canopy microsites are a favorable environment for establishment and growth of seeded bitterbrush and could be targeted for restoration efforts to improve efficiency.
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Following a wildfire, successful tree regeneration is mediated by multiple factors, from the microsite to landscape scale. This presentation demonstrates the importance of microsite conditions such as soil moisture and temperature in predicting conifer tree establishment. The speakers examined the footprint and behavior of a large 2018 wildfire in southern Colorado to understand how fire severity and post-fire logging influenced stand structure, fuels, vegetation, and soil microsite conditions. Their findings show that salvage-logged plots demonstrated lower daily average temperature and minimum soil moisture and higher fuel loading across most fuel size classes relative to unlogged plots, which also corresponded with a loss of dead standing wood and little to no canopy cover. Early post-fire conifer regeneration was low across all plots, but lower soil moisture and higher soil temperature negatively impacted the density of regeneration. Careful consideration of soil impacts and the associated changes to forest conditions should be taken when conducting post-fire logging to prevent detrimental effects on microsite conditions and forest recovery.
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Study found that expected sediment and phosphorus loads were lower under the scenario that emphasized thinning, whereas scenarios that increased prescribed burning resulted in loads that were comparable to scenarios that involved less treatment. These results reflect the finding from the WEPP analysis that prescribed burning is expected to reduce ground cover more than is thinning. Our analysis supports efforts to increase fuel reduction treatments to mitigate future wildfires, but it also suggests that preventative treatments may not avoid a long-term decline in water quality as wildfires increase with climate change.
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Join presenter Erica Fisher for a summary of what we know so far about how structures in wildfires influence our water infrastructure and what can be done to potentially stop further contamination from wildfire events.
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From following more than 1,500 wildfires, we find treatments were disproportionately applied in more stressful, degraded ecological conditions. Failure to incorporate unmeasured drivers of treatment allocation led to the conclusion that costly, widespread seedings were unsuccessful; however, after considering sources of bias, restoration positively affected sagebrush recovery. Treatment effects varied with climate, indicating prioritization criteria for interventions. Our findings revise the perspective that post-fire sagebrush seedings have been broadly unsuccessful and demonstrate how selection biases can pose substantive inferential hazards in observational studies of restoration efficacy and the development of restoration theory.