The Relative Impact of Human Disturbances on the Vegetation of a Large Wetland Complex

Anthropogenic disturbances are important factors structuring the vegetation of ecosystems, but their influence on peatlands remain poorly understood. We quantified the relative influence of anthropogenic disturbances, abiotic variables and spatial patterns on the floristic composition of a large wetland complex, and assessed the relationship between disturbances and species richness. Vegetation and abiotic data were collected in 253 plots, and disturbances determined using aerial photographs. Data were analyzed with multivariate and nonparametric techniques. Disturbances had detrimental effects on bryophyte and on true peatland species richness, but favored the richness of grass as well as non-peatland and exotic species. However, abiotic conditions are still predominant in controlling the overall plant composition at the complex level (25.2% of floristic variations explained, compared to 8.2% for disturbances). The vegetation heterogeneity was also mainly attributed to abiotic factors when taking account only fen habitats. The three sets of explanatory factors were equally important in structuring the vegetation of bog habitats. However, the most influential variables were those related to human activities. Our landscape ecology approach to study wetland vegetation allowed us to show that while human disturbances are important in structuring vegetation in bogs and fens, they do not override the prevalence of local abiotic conditions.

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