DOI: 10.5061/dryad.x0k6djhpr
title: Data archive for: Fire-regime variability and ecosystem resilience over four millennia in a Rocky Mountain subalpine watershed

description: Wildfires strongly influence forest ecosystem processes, including carbon
 and nutrient cycling and vegetation dynamics. As fire activity increases
 under changing climate conditions, the ecological and biogeochemical
 resilience of many forest ecosystems remains unknown. To
 investigate the resilience of forest ecosystems to changing climate and
 wildfire activity over decades to millennia, we developed a 4800-yr
 high-resolution lake-sediment record from Silver Lake, Montana, USA
 (47.360° N, 115.566° W). Charcoal particles, pollen grains, element
 concentrations, and stable isotopes of C and N serve as proxies of past
 changes in fire, vegetation, and ecosystem processes such as nitrogen
 cycling and soil erosion, within a small subalpine forest watershed. A
 published lake-level history from Silver Lake provides a local record of
 paleohydrology. A trend toward increased effective moisture over
 the late Holocene coincided with a distinct shift in the pollen assemblage
 c. 1900 yr BP, resulting from increased subalpine conifer abundance. Fire
 activity, inferred from peaks in macroscopic charcoal, decreased
 significantly after 1900 yr BP, from one fire event every 126 yr (83–184
 yr, 95% CI) from 4800–1900 yr BP, to one event every 223 yr (175–280 yr)
 from 1900 yr BP to present. Across the record, individual fire events were
 followed by two distinct decadal-scale biogeochemical responses,
 reflecting differences in ecosystem impacts of fires on watershed
 processes. These distinct biogeochemical responses were interpreted as
 reflecting fire severity, highlighting (i) erosion, likely from large or
 high-severity fires, and (ii) nutrient transfers and enhanced within-lake
 productivity, likely from lower-severity or patchier fires. Biogeochemical
 and vegetation proxies returned to pre-fire values within decades
 regardless of the nature of fire effects. Paleo records of fire
 and ecosystem responses provide a novel view revealing past variability in
 fire effects, analogous to spatial variability in fire severity observed
 within contemporary wildfires. Overall, the paleo record highlights
 ecosystem resilience to fire across long-term variability in climate and
 fire activity. Higher fire frequencies in past millennia relative to the
 20th and 21st centuries suggest that northern Rocky Mountain subalpine
 ecosystems could remain resilient to future increases in fire activity,
 provided continued ecosystem recovery within decades.
description: Data are paleoenvironmental
 proxies from a lake-sediment core collected at Silver Lake, Montana, USA,
 in 2017 (47.360° N, 115.566° W). Sediments ages were estimated from a
 bayesian age-depth model developed in <em>rbacon</em> using
 dates from Pb210 analysis of near-surface sediments and radiocarbon dating
 of terrestrial macrofossils or concentrated charcoal. Sediment subsamples
 were taken contiguously at 0.5-cm intervals throughout the core,
 representing an average of 10 years per sample, for macroscopic charcoal
 analysis, XRF analysis, and elemental and stable isotope analysis of C and
 N. Pollen grains were extracted and identified at c. 100 yr intervals to
 characterize the relative abundances of terrestrial pollen types over
 time. Additional data from published studies were also used in the
 analysis:  
 Parish, M. C., K. D. Wolf, P. E. Higuera, and B. N. Shuman.
 2022. Holocene water levels of Silver Lake, Montana, and the hydroclimate
 history of the Inland Northwest. Quaternary Research:1–13. [Data available
 from: https://www.ncei.noaa.gov/access/paleo-search/study/36593] 
description: All analyses are conducted in R v. 4.2.1.