Data and code for: Wildfire activity in northern Rocky Mountain subalpine forests still within millennial-scale range of variability
Data files
Aug 29, 2023 version files 637.90 KB
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AreaBurned_NR_1900_2020.csv
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AreaBurned_VPD_1984_2020.csv
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CompositeChar_NR.csv
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CompositeChar_SR.csv
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PeakData_NR.csv
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PeakData_SR.csv
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README_for_ClarkWolf_et_al_2023.docx
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README.md
Abstract
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 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 was 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 societal and ecological consequences of climatic warming in subalpine forests will depend, in large part, on the magnitude of fire-regime changes relative to the past.
Methods
We provide paleoecological fire-history data used to support the analyses and results in Clark-Wolf et al. (2023). These data are from 12 lake-sediment records from within a c. 11,000-ha landscape in the northern Rocky Mountains, USA, spanning 46.6 to 47.5° N and 114.6 to 116° W. Sediment cores were collected from the deepest part of each lake in 2017 to 2019. Sediment cores were dated based on 210Pb activity in the upper sediments, as well as tephra layers from known volcanic eruptions and 14C dating of terrestrial macrofossils or concentrated charcoal. Sediment cores were sliced at 0.5-cm intervals and subsampled contiguously for macroscopic charcoal analysis. Charcoal pieces were counted under a stereomicroscope and used to calculate charcoal accumulation rate, which was analyzed using peak detection methods to identify peaks in charcoal accumulation inferred as local fire events. To produce a composite record of fire history across the study area, the percent of sites recording local fires per century was calculated.
We also provide previously published data used in the analysis and figures presented in Clark-Wolf et al. (2023). These were obtained from publicly available datasets: MTBS [https://www.mtbs.gov], Northern Rockies Fire Atlas [https://doi.org/10.2737/RDS-2009-0006-2]), and gridMet [https://www.climatologylab.org/gridmet.html], as well as data obtained from archives associated with prior publications (Higuera et al. 2021 [https://doi.org/10.5061/dryad.rfj6q579n]).
Usage notes
Data are provided as .csv files, and code is provided as a .R script file to be opened in RStudio (open source).