Fire Ecology & Effects
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The good, bad, and ugly of fire and wildlife – roasty toasty critters or promoting sustainable habitat for expanding and healthy wildlife populations? Let’s discuss the pros and cons of fire on wildlife. How is the lack of fire at the necessary scale, frequency, intensity/severity, and seasonality one of the greatest threats to wildlife in fire-dependent ecosystems?
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Smoke characteristics improved predictions of fire severity in non-reburn areas but not in reburns. Maximum daily smoke cover interacted with elevation, showing a strong dampening effect of high smoke cover on fire severity at low elevations consistent with prior work and a weaker amplifying effect on fire severity at middle elevations with low smoke cover.
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A slight, gradual decline in total C and N was found with increasing temperature and heat duration, reaching a maximum loss of 14–18% of the total at the highest heat load. Available NH4 increased linearly starting at 150–175 °C and reached a maximum 15-fold increase relative to unburned soil by 450 °C. Nitrification (30-d post-fire) was low regardless of treatment and was essentially eliminated at the highest temperatures. Microbial biomass declined curvilinearly with increased heating, approaching 65% loss compared to unburned soil, and was most rapid in moist soil once temperatures exceeded 60–70 °C. Ultimately, we found no evidence of abrupt heat thresholds for these common soil properties. Instead, property changes followed a slightly declining trajectory (soil C, N, NO3, fungal hyphae) or a steady incremental increase (NH4) or decrease (microbial biomass).
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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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The Association for Fire Ecology (AFE) is excited to announce that the 10th International Fire Ecology and Management Congress will be held December 4-8, 2023 in Monterey, California at the Hyatt Regency Monterey Hotel. The Call for Proposals will open in January 2023.
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Monitoring Trends in Burn Severity (MTBS) includes all fires 1000 acres or greater in the west and 500 acres or greater in the east. The extent of coverage includes the continental U.S., Alaska, Hawai’i and Puerto Rico. MTBS data are freely available to the public.
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High severity wildfires led to the greatest decrease in cover for all plant functional types, while low severity wildfires caused the least decrease in the functional type cover in most cases, though some variations existed. Furthermore, the impacts of wildfires on vegetation cover were greater in woody (SHR and TREE) types than in herbaceous (AFG and PFG) types. Significant negative correlation existed between percent changes in AFG and PFG cover and SPEI indicating higher prefire soil moisture conditions likely increased fine fuel loads and led to a larger decrease in AFG and PFG cover following wildfires. Significant positive correlation existed between percent changes in SHR and TREE cover and SPEI indicating drier prefire conditions resulted in larger decreases in SHR and TREE cover following wildfires.
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We evaluated plant community succession following prescribed fire on Artemisia arbuscula var. arbuscula (low sagebrush) steppe in southeastern Oregon. Treatments were “prescribed burned” (burn; fall 2012) and “unburned” (control) low sagebrush a steppe, and the study design was a randomized complete block with 4 replicates per treatment. Herbaceous yield and vegetation canopy cover and density were compared between treatments (2012–2020). Fire practically eliminated low sagebrush and there was no recruitment of new plants in the first 8 years after burning. Herbaceous yield in the burn treatment was about double the control for most of the postfire period. Native perennial grasses and forbs constituted 94% to 96% and Bromus tectorum L. (cheatgrass) 0.2% to 2% of total herbaceous yield in the control. In the burn treatment, perennial grasses and forbs constituted 83% to 87%, native annual forbs 2% to 5%, and cheatgrass 3% to 9% of total herbaceous yield. Despite an increase in cheatgrass, the burned low sagebrush sites were dominated by herbaceous perennial grasses and forbs and exhibited high levels of resilience and resistance. After prescribed fire, for the study sites and comparable low sagebrush associations, weed control or seeding are not necessary to recover the native herbaceous community. However, the results in our study are for low-severity prescribed fire in intact low sagebrush plant communities. Higher-severity fire, as might occur with wildfire, and in low sagebrush communities having greater prefire invasive weed composition should not be assumed to develop similarly high levels of community resilience and resistance.
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o 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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2020 was a record year for wildfires in recent history, though the area burned was close to estimates of pre-suppression burning. We should expect more of these types of fire seasons in the future. Much of the burning was destructive rather than restorative and impacts to humans were severe.