Biogeochemical impacts of wildfires over four millennia in a Rocky Mountain subalpine watershed
2014
Dunnette, Paul V. | Higuera, Philip E. | McLauchlan, Kendra K. | Derr, Kelly M. | Briles, Christy E. | Keefe, Margaret H.
Wildfires can significantly alter forest carbon (C) storage and nitrogen (N) availability, but the long‐term biogeochemical legacy of wildfires is poorly understood. We obtained a lake‐sediment record of fire and biogeochemistry from a subalpine forest in Colorado, USA, to examine the nature, magnitude, and duration of decadal‐scale, fire‐induced ecosystem change over the past c. 4250 yr. The high‐resolution record contained 34 fires, including 13 high‐severity events within the watershed. High‐severity fires were followed by increased sedimentary N stable isotope ratios (δ¹⁵N) and bulk density, and decreased C and N concentrations – reflecting forest floor destruction, terrestrial C and N losses, and erosion. Sustained low sediment C : N c. 20–50 yr post‐fire indicates reduced terrestrial organic matter subsidies to the lake. Low sedimentary δ¹⁵N c. 50–70 yr post‐fire, coincident with C and N recovery, suggests diminishing terrestrial N availability during stand development. The magnitude of post‐fire changes generally scaled directly with inferred fire severity. Our results support modern studies of forest successional C and N accumulation and indicate pronounced, long‐lasting biogeochemical impacts of wildfires in subalpine forests. However, even repeated high‐severity fires over millennia probably did not deplete C or N stocks, because centuries between high‐severity fires allowed for sufficient biomass recovery.
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