More Like this

1. Long-term soil fungal community recovery after fire is impacted by climate change

   https://doi.org/10.1101/2020.10.09.333443  

   McGee, Spencer; Tidwell, Alyssa; Riggs, Erin; Veltkamp, Hannah; Zahn, Geoffrey (August 2022, Western North American naturalist)

   Though much is known about fungal importance to forest health, there is very little information about factors that impact recovery times of soil fungal communities after a fire. Soil samples were taken from burn sites within one ecotype of temperate coniferous forest in Utah over a 20-year chronosequence. Sites were selected from available historic burns and were similar in plant community structure, elevation, slope, and aspect. Fungal DNA from these samples was compared to soil from paired unburned sites nearby to measure community similarity and estimate soil fungal recovery rates. Differences between paired burned and unburned sites remained fairly stable over a decadal timescale overall, but fungal community structure was found to recover more quickly in areas with a higher average annual temperature. A significant positive correlation in community recovery was seen in areas with a difference of as little as 2 °C per year. The only other environmental variable that significantly interacted with time since burn was annual mean precipitation. As global temperatures increase, alpine fires are increasing as well, but these results suggest that fungal community recovery time will be shortened under new climate scenarios. 

   more » « less
2. Unearthing the legacy of wildfires: post fire pyrogenic carbon and soil carbon persistence across complex Pacific Northwest watersheds

   https://doi.org/10.1007/s10533-024-01151-1  

   Peter-Contesse, Hayley; Lajtha, Kate; Boettcher, Aron; O’Kelley, Regina; Mayedo, Amy (May 2024, Biogeochemistry)

   Abstract Wildfires have the potential to dramatically alter the carbon (C) storage potential, ecological function, and the fundamental mechanisms that control the C balance of Pacific Northwest (PNW) forested ecosystems. In this study, we explored how wildfire influences processes that control soil C stabilization and the consequent soil C persistence, and the role of previous fire history in determining soil C fire response dynamics. We collected mineral soils at four depth increments from burned (low, moderate, and high soil burn severity classes) and unburned areas and surveyed coarse woody debris (CWD) in sites within the footprint of the 2020 Holiday Farm Fire and in surrounding Willamette National Forest and the H.J. Andrews Experimental Forest. We found few changes in overall soil C pools as a function of fire severity; we instead found that unburned sites contained high levels of pyrogenic C (PyC) that were commensurate with PyC concentrations in the high severity burn sites—pointing to the high background rate of fire in these ecosystems. An analysis of historical fire events lends additional support, where increasing fire count is loosely correlated with increasing PyC concentration. An unexpected finding was that PyC concentration was lower in low soil burn severity sites than in control sites, which we attribute to fundamental ecological differences in regions that repeatedly burn at high severity compared with those that burn at low severity. Our CWD analysis showed that high mean fire return interval (decades between fire events) was strongly correlated with low annual CWD accumulation rate; whereas areas that burn frequently had a high annual CWD accumulation rate. Within the first year postfire, trends in soil density fractions demonstrated no significant response to fire for the mineral-associated organic matter pool but slight increases in the particulate pool with increasing soil burn severity—likely a function of increased charcoal additions. Overall, our results suggest that these PNW forest soils display complex responses to wildfire with feedbacks between CWD pools that provide varying fuel loads and a mosaic fire regime across the landscape. Microclimate and historic fire events are likely important determinants of soil C persistence in these systems. 

   more » « less
3. A bird’s eye view of ecosystem conversion: Examining the resilience of piñon-juniper woodlands and their avian communities in the face of fire regime change

   https://doi.org/10.1016/j.foreco.2023.121368  

   Woolet, Jamie; Stevens-Rumann, Camille S; Coop, Jonathan D; Pejchar, Liba (August 2023, Forest Ecology and Management)

   Climate change and land-use legacies have caused a shift in wildfires and post-fire growing conditions. These changes have strong potential to diminish the resilience of many ecosystems, with cascading effects and feedbacks across taxa. Piñon-juniper (PJ) woodlands are a diverse and widespread forest type in the western US and are home to many obligate and semi-obligate bird species. As such, this system is ideal for understanding wildfire resilience, or lack thereof, in terms of both vegetation and wildlife associations. This study evaluated post-fire vegetation structure and associated avian communities following three wildfires; one that burned one year prior to sampling (recent fire), and two that burned approximately 25 years previously (old fires). Vegetation characteristics and the habitat use of PJ-associated bird species were compared across severely burned patches, unburned refugia, and unburned sites outside of the burn perimeter. We expected wildfire to alter vegetation and bird usage for the first few years post-fire, which we observed in our recent burns. However, even 25-years post-fire, little recovery to PJ woodland had occurred and the associated bird communities had not returned, compared to unburned areas. No piñon regeneration was observed in any burned areas and no juniper regeneration in the recent fire. Piñon seedling densities in unburned sites and refugia averaged 80 ha−1 and 151 ha−1, respectively, while juniper seedling densities were 220 ha−1 in both habitat types. Habitat use for thirteen PJ-associated species were modeled, three of which (Woodhouse’s Scrub Jay, Ash-throated Flycatcher, and Virginia’s Warbler) used all habitats. Four species (American Robin, Gray Vireo, Black-throated Gray Warbler, and Gray Flycatcher) were essentially absent from the old burn habitat, reflecting species-specific need for mature piñon or juniper trees and/or greater canopy cover. Conversely, birds that were present in the old burn habitat (including Virginia’s Warbler, Blue-gray Gnatcatcher, Woodhouse’s Scrub-jay, Ash-throated Flycatcher, and Spotted Towhee) are typically associated with habitat edges, high shrub cover, or cavity nests. Altered vegetation structure and bird habitat use in burned areas 25 years post-fire are evidence for enduring conversion to non-forest vegetation types. However, unburned refugia embedded in burned areas maintain forest attributes and support obligate bird communities, supporting ecological function and biological diversity. 

   more » « less
4. Evaluating the Recovery of Hydraulic Conductivity in Fire-Affected Soils

   Gerdes, Nolan; Webb, Ryan; Liston, Glen; Mooney, Kori (September 2024, McNair Scholars research journal)

   In the natural environment, wildfires affect how water interacts with soil leading to potentially catastrophic phenomena such as flooding, debris flows, and decreased water quality. Wildfires can cause soil sealing from increased soil water repellency, which in turn reduces infiltration and increases flood risk during rainfall. A 2017 meta-analysis found two properties that were affected by soil burning processes: Sorptivity (the capacity of a soil to absorb or desorb liquid by capillarity, S) and hydraulic conductivity (the ability for soil to transmit water when saturated, Kfs). Changes in these properties act synergistically to reduce infiltration, which increases erosion by accelerating and amplifying surface runoff. Thus, this research seeks to understand how soils subjected to severe burning compare to unburned soils. Using a mini-disk infiltrometer, field tests measured hydraulic conductivity of soils burned under slash and burn piles during the winters of 2016-17, 2020-21, and 2023-23 to better understand changes that occur in soil-hydraulic properties over time. These slash and burn piles served as approximate impacts for wildfires. Slash and burn piles also allow for paired measurements of unburned soils immediately adjacent to the burned area. Hydraulic conductivity was not significantly different when comparing burned and unburned soils 1 year after being burned. However, there was a significant difference between the hydraulic conductivity of soils burned 3 years ago compared to both unburned soil and soils burned 1 year ago. This suggests an interim process between 1- and 3-years post-burn that reduces hydraulic conductivity of burned soils. 

   more » « less
5. How interactions between wildfire and seasonal soil moisture fluxes drive nitrogen cycling in Northern Sierra Nevada forests

   https://doi.org/10.1071/WF21064  

   Brady, Mary K.; Hanan, Erin J.; Dickinson, Matthew B.; Miesel, Jessica R.; Wade, Laura; Greenberg, Jonathan (January 2022, International Journal of Wildland Fire)

   As wildfires become larger and more severe across western North America, it grows increasingly important to understand how they will affect the biogeochemical processes influencing ecosystem recovery. Soil nitrogen (N) cycling is a key process constraining recovery rates. In addition to its direct responses to fire, N cycling can also respond to other post-fire transformations, including increases or decreases in microbial biomass, soil moisture, and pH. 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 mineralisation, 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 mineralisation 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. 

   more » « less