Regular surface patterning of peatlands: Confronting theory with field data

Regular spatial patterns of sharply bounded ridges and hollows are frequently observed in peatlands and ask for an explanation in terms of underlying structuring processes. Simulation models suggest that spatial regularity of peatland patterns could be driven by an evapotranspiration-induced scale-dependent feedback (locally positive, longer-range negative) between ridge vegetation and nutrient availability. The sharp boundaries between ridges and hollows could be induced by a positive feedback between net rate of peat formation and acrotelm thickness. Theory also predicts how scale-dependent and positive feedbacks drive underlying patterns in nutrients, hydrology, and hydrochemistry, but these predictions have not yet been tested empirically. The aim of this study was to provide an empirical test for the theoretical predictions; therefore, we measured underlying patterns in nutrients, hydrology, and hydrochemistry across a maze-patterned peatland in the Great Vasyugan Bog, Siberia. The field data corroborated predicted patterns as induced by scale-dependent feedback; nutrient concentrations were higher on ridges than in hollows. Moreover, diurnal dynamics in water table level clearly corresponded to evapotranspiration and showed that water levels in two ridges were lower than in the hollow in between. Also, the data on hydrochemistry suggested that evapotranspiration rates were higher on ridges. The bimodal frequency distribution in acrotelm thickness indicated sharp boundaries between ridges and hollows, supporting the occurrence of a positive feedback. Moreover, nutrient content in plant tissue was most strongly associated with acrotelm thickness, supporting the view that positive feedback further amplifies ridge-hollow differences in nutrient status. Our measurements are consistent with the hypothesis that the combination of scale-dependent and positive feedback induces peatland patterning.