Modelling effects of litter quality and environment on peat accumulation over different time-scales

1 A model was developed that simulates the production and decay of annual peat cohorts over time-scales from years to millennia. The model was used to investigate potential effects of environment and litter-quality related parameters on peat accumulation, and to examine how well past changes in net accumulation can be reconstructed from the peat core record. 2 Sensitivity analysis of the model indicates that the relative ability of different input parameters to increase peat accumulation changed over time. Short-term results, e.g. from litter decomposition studies, therefore cannot be extrapolated to predict peat accumulation over longer time-scales. 3 In simulations that examined the long-term development of static community types, peat accumulation responded more strongly to water table position in bogs than in fens. In several cases, the relative peat accumulation potential of different community types changed over time. 4 Successional change (fen to bog) increased or decreased net peat accumulation, depending on the water table of the simulated bog. If succession was accompanied by lowered water tables, modelled peatlands showed a net loss of organic matter over extended periods of time. Effects of decreased litter quality in drier communities were outweighed by decreased productivity and greater decomposition in the thicker acrotelm. 5 Plots of cumulative organic matter mass vs. age for simulated profiles were often 'concave', as predicted by models that assume continued decomposition of deep peat. However, simulations that involved community change violated the assumptions of such models, and reconstructed actual (net) rates of organic matter accumulation were unreliable in spite of excellent model fits. 6 Current peat accumulation models often assume that environmental change will affect productivity, but not the botanical composition of peatland communities. Over decadal and centennial time-scales, however, community change will probably play a key role in determining peatland responses to climate change. Results obtained here suggest that interactions between environmental and community-based controls are complex, and their net effect may not be predictable from current data. In order to develop predictive models that work over these time-scales, we need a better understanding of feedback mechanisms between hydrology, community composition, and organic matter accumulation in peatlands.