Wetland chronosequence as a model of peatland development: Vegetation succession, peat and carbon accumulation

Peatlands form currently a major terrestrial pool of organic matter (OM) and carbon (C). Dynamics of peat accumulation processes can be approached via models, which, however, need to be evaluated against real data. Land uplift coast with ongoing primary peatland formation is a unique setting to study the patterns and controls of peatland vegetation succession, development from fen to bog, and consequent changes in peat, carbon (C) and nitrogen (N) accumulation. Here we compared a chronosequence of peatlands with a vertical peat sequence and ran Holocene Peatland Model (HPM) simulations, and evaluated the simulation against the field observations. The modern vegetation from the emergent sea shore to a bog with age of about 3000 years formed a continuum from minerotrophic to ombrotrophic plant communities. Similar sequence of plant communities was found in historical vegetation data. Along the chronosequence the fen-bog transition stage was most diverse regarding to plant community types, but also to spatial variability in peat height and water table depth (WTD). The transition from meadow to fen communities was associated with the establishment of Sphagnum moss patches. Palaeobotanical evidence from the bog site showed a rapid and quite recent fen-bog transition indicated by coinciding decrease in minerotrophic plant functional types (sedge) and increase in ombrotrophic plant functional types (lawn or hummock Sphagna). Concurrent vegetation transition also in the cores from younger, a 700 year old, fen site suggests different pace of succession in these age cohorts, possibly due to external forcing. Evaluation of the HPM simulations indicated that the model is adjustable and it produced reasonable predictions despite temperature not being included directly in the model.