Reduced fire severity offers near-term buffer to climate-driven declines in conifer resilience across the western United States

Davis, Kimberley T.; Robles, Marcos D.; Kemp, Kerry B.; Higuera, Philip E.; Chapman, Teresa B.; Metlen, Kerry L.; Peeler, Jamie L.; Rodman, Kyle C.; Woolley, Travis J.; Addington, Robert N.; Buma, Brian; Cansler, C. Alina; Case, Michael J.; Collins, Brandon M.; Dobrowski, Solomon Z.; Gill, Nathan S.; Haffey, Collin; Harris, Lucas B.; Harvey, Brian; Haugo, Ryan D.; Hurteau, Matthew D.; Kulakowski, Dominik; Littlefield, Caitlin E.; McCauley, Lisa A.; Povak, Nicholas A.; Shive, Kristen L.; Smith, Edward B.; Stevens, Jens T.; Stevens‐Rumann, Camille S.; Taylor, Alan H.; Tepley, Alan J.; Young, Derek J. N.; Andrus, Robert A.; Battaglia, Michael A.; Berkey, Julia K; Busby, Sebastian; Carlson, Amanda R.; Chambers, Marin E.; Dodson, Erich Kyle; Donato, Daniel C.; Downing, William M.; Fornwalt, Paula J.; Halofsky, Joshua S.; Hoffman, Ashley E.; Holz, Andrés; Iniguez, José M.; Krawchuk, Meg A.; Kreider, Mark R.; Larson, Andrew J.; Meigs, Garrett W.; Roccaforte, John Paul; Rother, Monica T.; Safford, Hugh D.; Schaedel, Michael S.; Sibold, Jason S.; Singleton, Megan P.; Turner, Monica G.; Urza, Alexandra K.; Wolf, Kyra D.; Yocom, Larissa L.; Fontaine, Joseph B.; Campbell, John L.

doi:10.1073/pnas.2208120120

Cited by 80 publications

(52 citation statements)

References 75 publications

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“…To quantify the effects of the modified algorithm on post-fire regeneration, including changes in aboveground biomass across the landscape, we used species-specific model outputs of plant establishment and aboveground biomass. We specifically selected the most common tree species in this region (piñon, ponderosa pine, and Douglas-fir), which are being impacted by large stand-replacing fires and have low regeneration in high-severity burn patches following wildfire (Brown & Wu, 2005;Davis et al, 2023;Korb et al, 2019;Petrie et al, 2016;Rocca et al, 2014). We used raster model output of the number of cohorts to examine how the modified regeneration algorithm influenced establishment relative to the original regeneration algorithm.…”

Section: Discussionmentioning

confidence: 99%

Topographic information improves simulated patterns of post‐fire conifer regeneration in the southwest United States

Jung

Keyser

Remy

et al. 2023

Global Change Biology

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The western United States is projected to experience more frequent and severe wildfires in the future due to drier and hotter climate conditions, exacerbating destructive wildfire impacts on forest ecosystems such as tree mortality and unsuccessful post‐fire regeneration. While empirical studies have revealed strong relationships between topographical information and plant regeneration, ecological processes in ecosystem models have either not fully addressed topography‐mediated effects on the probability of plant regeneration, or the probability is only controlled by climate‐related factors, for example, water and light stresses. In this study, we incorporated seedling survival data based on a planting experiment in the footprint of the 2011 Las Conchas Fire into the Photosynthesis and EvapoTranspiration (PnET) extension of the LANDIS‐II model by adding topographic and an additional climatic variable to the probability of regeneration. The modified algorithm included topographic parameters such as heat load index and ground slope and spring precipitation. We ran simulations on the Las Conchas Fire landscape for 2012–2099 using observed and projected climate data (i.e., Representative Concentration Pathway 4.5 and 8.5). Our modification significantly reduced the number of regeneration events of three common southwestern conifer tree species (piñon, ponderosa pine, and Douglas‐fir), leading to decreases in aboveground biomass, regardless of climate scenario. The modified algorithm decreased regeneration at higher elevations and increased regeneration at lower elevations relative to the original algorithm. Regenerations of three species also decreased in eastern aspects. Our findings suggest that ecosystem models may overestimate post‐fire regeneration events in the southwest United States. To better represent regeneration processes following wildfire, ecosystem models need refinement to better account for the range of factors that influence tree seedling establishment. This will improve model utility for projecting the combined effects of climate and wildfire on tree species distributions.

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Section: Discussionmentioning

confidence: 99%

Topographic information improves simulated patterns of post‐fire conifer regeneration in the southwest United States

Jung

Keyser

Remy

et al. 2023

Global Change Biology

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“…State changes (e.g. forest to grassland) may be more likely caused by climate-driven recruitment failure (Davis et al 2023) than seed availability from lack of refugia. An notable exception is that there was an increase in the maximum distance to refugia, driven by extreme values (i.e.…”

Section: Discussionmentioning

confidence: 99%

“…Overall, the results of this study imply that there are substantial refugia areas that could be used in planning for recovery or restoration efforts. Because post-fire climate conditions may restrict regeneration (Davis et al 2019), it is important to place remaining refugia in areas with better microclimates and lower fire severity, facilitating enhanced regeneration (Davis et al 2023). Future efforts should explore the persistence of refugia, whether finer-scale resolution data (e.g., at the tree level) reveal different trends in refugia, and whether changes within the forest land cover class can explain some of the patterns.…”

Section: Discussionmentioning

confidence: 99%

Fire refugia are robust across Western US forested ecoregions, 1986–2021

Platt,

Chapman,

Balch

2023

Environ. Res. Lett.

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In the Western US, area burned and fire size have increased due to the influences of climate change, long-term fire suppression leading to higher fuel loads, and increased ignitions. However, evidence is less conclusive about increases in fire severity within these growing wildfire extents. Fires burn unevenly across landscapes, leaving islands of unburned or less impacted areas, known as fire refugia. Fire refugia may enhance post-fire ecosystem function and biodiversity by providing refuge to species and functioning as seed sources after fires. In this study, we evaluated whether the proportion and pattern of fire refugia within fire events have changed over time and across ecoregions. To do so, we processed all available Landsat 4–9 satellite imagery to identify fire refugia within the boundaries of large wildfires (405 ha+) in 16 forested ecoregions of the Western US. We found a significant change in % refugia from 1986–2021 only in one ecoregion—% refugia increased within fires in the Arizona/New Mexico Mountain ecoregion (AZ/NM). Excluding AZ/NM, we found no significant change in % refugia across the study area. Furthermore, we found no significant change in mean refugia patch size, patch density, or mean distance to refugia. As fire size increased, the amount of refugia increased proportionally. Evidence suggests that fires in AZ/NM had a higher proportion of reburns and, unlike the 15 other ecoregions, fires did not occur at higher elevation or within greener areas. We suggest several possibilities for why, with the exception of AZ/NM, ecoregions did not experience a significant change in the proportion and pattern of refugia. In summary, while area burned has increased over the past four decades, there are substantial and consistent patterns of refugia that could support post-fire recovery dependent on their spatial patterns and ability to function as seeds sources for neighboring burned patches.

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“…Species composition in Northern Rockies subalpine forests has remained relatively stable over the past several millennia [62,74], when fire activity was similar to or greater than that of the 21 st century (figure 3). Additionally, although the combination of warming and drying and higher fire activity can limit recruitment of subalpine species [75][76][77][78], future climate is projected to remain suitable for tree regeneration in the Northern Rockies through at least mid-century [79]. Therefore, Northern Rockies subalpine forests could remain resilient to modest increases in burning in the near term; increases in fire activity that move the system outside of the HRV, however, have the potential to initiate large-scale ecological transformations, particularly in the context of overall climate warming [80,81].…”

Section: Historical Contemporary and Future Fire Activity In The Nort...mentioning

confidence: 99%

Wildfire activity in northern Rocky Mountain subalpine forests still within millennial-scale range of variability

Wolf

Higuera

Shuman

et al. 2023

Environ. Res. Lett.

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Increasing area burned across western North America raises questions about the precedence and magnitude of changes in fire activity, relative to the historical range of variability (HRV) that ecosystems experienced over recent centuries and millennia. Paleoecological records of past fire occurrence provide context for contemporary changes in ecosystems characterized by infrequent, high-severity fire regimes. Here we present a network of 12 fire-history records derived from macroscopic charcoal preserved in sediments of small subalpine lakes within a c. 10,000 km2 landscape in the U.S. northern Rocky Mountains (Northern Rockies). We used this network to characterize landscape-scale burning over the past 2500 yr, and to evaluate the precedence of widespread regional burning experienced in the early 20th and 21st centuries. We further compare the Northern Rockies fire history to a previously published network of fire-history records in the Southern Rockies. In Northern Rockies subalpine forests, widespread fire activity was strongly linked to seasonal climate conditions, in contemporary, historical, and paleo records. The average estimated fire rotation period (FRP) over the past 2500 years was 164 yr (HRV: 127-225 yr), while the contemporary FRP from 1900-2021 CE was 215 yr. Thus, extensive regional burning in the early 20th century (e.g., 1910 CE) and in recent decades remains within the HRV of recent millennia. Results from the Northern Rockies contrast with the Southern Rockies, which burned with less frequency on average over the past 2500 yr, and where 21st-century burning has exceeded the HRV. Our results support expectations that Northern Rockies fire activity will continue to increase with climatic warming, surpassing historical burning if more than one exceptional fire year akin to 1910 occurs within the next several decades. The ecological consequences of climatic warming in subalpine forests will depend, in large part, on the magnitude of fire-regime changes relative to the past.

show abstract

Reduced fire severity offers near-term buffer to climate-driven declines in conifer resilience across the western United States

Cited by 80 publications

References 75 publications

Topographic information improves simulated patterns of post‐fire conifer regeneration in the southwest United States

Topographic information improves simulated patterns of post‐fire conifer regeneration in the southwest United States

Fire refugia are robust across Western US forested ecoregions, 1986–2021

Wildfire activity in northern Rocky Mountain subalpine forests still within millennial-scale range of variability

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