World wetlands classification: a new hierarchic hydro-ecological approach

Many different approaches to classify wetlands at regional and global levels have been proposed, but their use of different classification parameters complicates comparisons of the results. Moreover, none of the international approaches cover global wetland variety with respect to size and environmental conditions. A comparison shows that hydrology is the only parameter that can be used for a hierarchic classification on a global scale. In the approach presented herein, differentiation between coastal, inland and anthropogenic wetlands is proposed. The use of higher classification units (systems, subsystems, orders, suborders and classes) is based on hydrological parameters. Wetlands are separated into small, simply structured types treated by all classification systems, and large wetscapes that, due to their complexity, are not. However, wetscapes represent well-defined landscape units, many of which are the focus of international organizations involved in wetland protection. They have to be treated using a holistic approach given the many interactions of their ecological subunits, their role in regional economies, their targeting by legislation and their value to humans. Considering the large gaps in knowledge about wetlands at a global scale, the new approach is a powerful tool for its classification, because it is flexible enough to include additional classification units, as required. Local classification systems can eliminate higher categories, which do not occur in their regions. Classification at lower rankings (functional units, subclasses, macrohabitats) can be introduced using additional classification parameters such as vegetation, soils and water chemistry. Examples from Brazil are provided.