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 gCO2m-2yr-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-2 yr-1 (4-90%) to gross ecosystem photosynthetic production (GPP), and R from 1263 to 2813 gCO2m-2 yr-1 (70-98%) to gross ecosystem respiration (GR). © Journal compilation © 2007 Blackwell Munksgaard.