Studying self-organized patterning of peatland ecosystems with Appropriate Complexity Landscape Modeling

Maarten Eppinga
Department of Geography, University of Zurich, 8047 Zurich, Switzerland

The surface of northern and tropical peatland ecosystems frequently exhibits self-organized patterning of densely vegetated hummocks and more sparsely vegetated hollows. Theoretical studies so far suggest multiple alternative mechanisms that could be driving this pattern formation. The long time span associated with peatland surface pattern formation, however, limits possibilities for empirically testing cause-effect relationships through field manipulations. We present a reaction-advection-diffusion model that describes spatial interactions between vegetation, nutrients, hydrology, and peat. Modification of the model’s reaction terms and the hydraulic conductivity function enable the study of pattern formation as driven by three different mechanisms: peat accumulation, water ponding, and nutrient accumulation. By on-and-off switching of each mechanism, we created a full-factorial design to see how these mechanisms affected surface patterning (pattern of vegetation and peat height) and underlying patterns in nutrients and hydrology.

Results revealed that different combinations of structuring mechanisms lead to similar types of peatland surface patterning but contrasting underlying patterns in nutrients and hydrology. These contrasting underlying patterns suggested that the presence or absence of the structuring mechanisms can be identified by relatively simple short-term field measurements of nutrients and hydrology, meaning that longer-term field manipulations could be circumvented. Performing these empirical tests in similarly patterned peatland complexes along a Eurasian climatic gradient, we found that the underlying patterns in nutrients and hydrology reversed along the climatic gradient, corroborating the main prediction of the model framework.

This study follows the Appropriate Complexity Landscape Modelling approach, in that it explores multiple pattern-forming mechanisms in a model environment, and subsequently confront these predictions to empirical data. This approach may not only be useful for northern peatlands but for (sub)tropical peatlands as well. This notion is illustrated with current work in progress, in which we study multiple mechanisms that may drive peatland pattern formation in the Florida Everglades.