Document: DAV-3-68-30

Response of boreal forest soil CO₂ efflux to experimental wildfire (Frostfire) in an interior Alaska watershed.

VALENTINE, D.W.* and R.D.BOONE

University of Alaska, Fairbanks, AK 99775, USA ¹

Abstract:
We assessed the response of mid-day net soil CO₂ efflux (respiration-photosynthesis) under two contrasting vegetation types to an experimental wildfire of moderate intensity as part of the Frostfire project. In 1998 and 1999, late growing season soil CO₂ effluxes in three unburned replicate sites under mixed hardwood (MH; Betula papyrifera and Populus tremuloides) averaged 110-150 mg C m^-2 h^-1. These rates were 2-3 times higher than under closed canopy black spruce (CBS; Picea mariana and mixed shrubs). Growing season soil temperatures at any given depth were higher in MH than in CBS sites owing to an insulating moss layer, and peak correlations between CO₂ efflux rates and soil temperatures occurred closer to the soil surface in MH than in CBS sites. In July 1999, the moderately intense fire killed all vegetation and thinned the CBS moss layer by an average of 5.5-6.5 cm. The fire halved soil CO₂ effluxes from MH sites and reduced soil CO₂ effluxes from burned CBS sites slightly but significantly (p<0.05). Decreased CO₂ efflux probably resulted from fire-induced cessation of root respiration rather than reduced decomposition in both MH and CBS vegetation types. The thinning of the CBS moss layer both reduced insulation and eliminated moss and herb photosynthesis; both may have contributed to offsetting root respiration declines.

Keywords: fire, soil carbon balance

This abstract is being presented at: 9:00 AM in session:
Oral Session #71: Soil Microbial Biomass and Soil Respiration.