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

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 (GPP), and R from 1263 to 2813 gCO₂m⁻²yr⁻¹ (70–98%) to gross ecosystem respiration (GR). [ABSTRACT FROM AUTHOR]