Modeling the role of ecological succession in peatland carbon cycle responses to rapid and long term hydrological change

Peatlands cover large areas and contain a significant fraction of total carbon in boreal regions. Long-term changes in hydrology can drive shifts in plant communities and soil properties. Ecosystem CO2 flux responses to hydrological change depend on a balance between productivity and respiration responses. We used the LANDIS-II model, a forest succession and carbon cycling model, to evaluate the role of peatland succession in regional carbon budgets in northern Wisconsin, USA.

Distribution functions of soil height were used to determine fractional areas of wetland ecosystem types, and plant growth and establishment parameters were set to reflect the area of optimal habitat for each species. Fractional areas were then changed over time to investigate different scenarios of long-term changes in water table level, allowing species composition to change in response to changing conditions. Responses of soil decomposition rate to water table changes were calculated by dividing soil into wet and dry fractions with different decomposition rates.

Climate change predictions include potential changes in hydrology over both long and short time scales. Greater incidence of severe droughts could cause short-term declines in water table, while increased mean temperature could cause long-term water table declines through increased evapotranspiration. Results suggested that long-term declining water table in peatlands initially results in increased CO2 uptake as more productive tree species establish and grow. However, more rapid drying can lead to significant carbon loss from the ecosystem as increased soil decomposition dominates the CO2 budget. These results suggest that dynamic vegetation should be included in estimates of peatland responses to climatic and hydrological change, and that the time scale of changes determines the ecosystem response.