Seasonal and spatial variations of carbon fluxes of arctic and boreal ecosystems in Alaska

Arctic and Boreal ecosystems are now responding to ongoing rapid and drastic warming. To reveal the current state of the carbon fluxes at both spatial and temporal scales, we have synthesized data on the carbon fluxes measured at seven arctic tundra and five boreal ecosystems across Alaska, and identified seasonal and spatial variations of the carbon fluxes and its environmental controlling factors. At current state, all the boreal and six of seven arctic tundra ecosystems acted as a carbon sink during the vegetation growing season, implying that the ecosystems did not substantially emit the carbon owing to the stimulated decomposition by the current warming, although there were much of uncertainties in the winter flux. The spatial variation of the carbon sink was determined by ecosystem respiration (RE) rather than gross primary productivity (GPP) for the even-aged boreal and tundra ecosystems. For the burned forests, the difference of GPP was much greater than that of RE; thus GPP substantially influenced the sink during the recovery after stand replacing fire. Among the tundra and boreal ecosystems except the recently disturbed forests, the spatial variations of GPP and RE were generally explained by those of growing degree days (GDD), implying that the temperature condition was a primary regulation factor to the carbon fluxes at this spatial scale. For understanding the spatial distributions of the carbon fluxes and its linkage to the climate, we will scale up the carbon fluxes by using satellite remote sensing, and discuss possible important processes in the Arctic and boreal ecosystems.