DOI: 10.5061/dryad.3n5tb2rnv
title: Data and code for: Wildfire activity in northern Rocky Mountain subalpine forests still within millennial-scale range of variability

description: 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.
description: 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]).
description: Data are provided as .csv files, and code is provided as a .R
 script file to be opened in RStudio (open source).