Forest floor versus ecosystem CO₂ exchange along boreal ecotone between upland forest and lowland mire

Abstract

We determined the landscape variation of forest floor (FF) CO₂ uptake (photosynthesis, P), FF CO₂ emission (respiration, R) in relation to net ecosystem CO₂ exchange (NEE) and environmental factors along a forest-mire ecotone in Finland. The 450 m long ecotone extended from xeric, upland pine dominated habitats, through spruce and transitional spruce-pine-birch forest, to sedge peatlands downslope. The CO₂ fluxes were measured at nine stations during 2005 using chamber and IR techniques. Instantaneous P and R measurements for each station were interpolated by fitting their response to continuous records of light (mean R² = 0.66) and temperature (mean R² = 0.77) recorded nearby to give annual estimates. Stand biomass increment was used to estimate the annual CO₂ exchange contribution of the trees. Annual P values from -307 to -1632 gCO₂m^-2yr^-1 were inversely correlated with FF light (r = -0.96), FF above-ground biomass (r=-0.92) and canopy openness (r=-0.95). Annual R values from 1263 to 2813 gCO₂ m^-2 yr^-1 were correlated with tree stand foliar biomass (r = 0.77). Estimated NEE values varied from 546 to -1679 gCO₂m^-2/yr^-1, with P contributing from -307 to -1632 gCO₂m^-2yr^-1 (4–90%) to gross ecosystem photosynthetic production, and R from 1263 to 2813 gCO₂m^-2yr^-1 (70–98%) to gross ecosystem respiration (GR).