| The surfaces of boreal peatlands are frequently hummocky. Their hummocks and hollows develop from the peat and remain stable over long periods of time, even while climate and other environmental conditions change. Processes leading to these stable surface forms have not been understood. The HOllow-HUMmock (HOHUM) model was developed to investigate the causes of their resilience and stability.; HOHUM is a dynamic, process-based simulation model applicable to bog sites throughout the world. It simulates Sphagnum moss growth and decay in response to local climate. The hydrology submodel calculates seasonal water table fluctuations; the vegetation submodel grows Sphagnum moss using climatic and moisture, and the peat decomposition-accumulation submodel simulates layer-specific peat decay and accumulation. The model tracks the total depth of the top layer of bogs for three types of Sphagnum mosses, those forming high hummocks, lower or middle hummock layers, and hollows.; Model results indicate that resilience results from interactions between moisture, Sphagnum biology, and decomposition. Feedbacks between Sphagnum growth, decay, and moisture restrict peat accumulation over time, creating a stable equilibrium with local climate within decades.; Model tests show excellent agreement between predicted and measured heights of hummocks and hollows for North American and European sites. Sensitivity tests indicate that the model is most sensitive to precipitation, decomposition rates, peat temperature, estimates of maximum Sphagnum production rates, peat bulk densities, and retention of ice cores into the spring. Simulation results for 35 northern U.S. and Canadian sites indicate that boreal climate regions generate distinct bog surfaces. To the south, hollow species drop out, leaving the more drought-tolerant species to form relatively flat surfaces, or lawns. Bogs in the far north display little surface relief, and to the northwest, arctic conditions prevent bog formation. These simulated geographic patterns are similar to those reported for North American bogs.; Evidence from HOHUM indicates that feedbacks inherent in the peatland ecosystem are adequate to compensate for the magnitudes of changes in climate predicted by global climate change models. It is unlikely that massive releases of carbon will occur, as has been feared regarding climate change. |
