Significant effects of patch geometry and spatial arrangement of wetland ecosystems on plant diversity

In Switzerland, approximately 90% of all wetlands have disappeared since 1850, and the remaining wetlands are threatened because of their fragmentation and isolation. In 36 wetlands differing in management regime and altitude, we examined how landscape patterns (wetland size, shape and distance to other wetlands) influence plant diversity (species richness and Shannon index of vascular plants and bryophytes) at the level of entire wetlands. A first survey was conducted in 1996 and 10 years later, in 2005-2006, we repeated the surveys to obtain a database for spatial and temporal comparisons. Using this database and applying ArcGIS and FRAGSTAT to quantify landscape patterns, we tested whether more species have been lost from smaller or more isolated wetlands than from larger or less isolated ones and compared species similarity among sites with different distance to each other. Plant species richness declined with increasing ratio of perimeter/area of wetlands. The Shannon index of plant species diversity was higher in target wetlands with shorter distance to a neighboring one (P < 0.05). Furthermore, species richness in target wetlands increased with the number of neighboring wetlands within a 2000 m radius (P < 0.05). There was also significant nearest distance x area interaction (P < 0.05) affecting the species richness of plant species diversity. That is, in small wetlands with long distance to the next one, species richness was particularly low. These results indicate that for conservation planning not only direct area effects but also effects of shape and spatial arrangement should be taken into account.