Turbary Restoration Meets Variable Success: Does Landscape Structure Force Colonization Success of Wetland Plants?

Peat ponds have been restored widely in the Netherlands to enhance the available habitat for species-rich plant communities that characterize the early succession stages toward land. Colonization success of 33 target aquatic species has been quantified in eight complexes of new ponds. It has been related to the lay-out of these ponds, the structure of the surrounding landscape, (historic) prevalence of source populations within the complex and within a perimeter of 10 km, and pond water quality. Colonization success was variable: between 6 and 26 target species had reached the complexes in 1998. This success was coupled to the first principal component (PC) in a principal component analysis (PCA) explaining 44% of the variation in 27 variables. This first PC correlated with historical perimeter and local within-complex species richness, the number of ponds in the complex, the SW orientation of ditches in these complexes and pH, and transparency of the water. Age of the ponds (1-9 years), area of open water (8-42%), and shoreline density (13-43 km/km2 in the complex) did not contribute significantly to colonization success. Separation of the effect of a species-rich surrounding landscape, the possibility to disperse through that landscape, the spatial lay-out of the complex and transparency of the water were precluded by the strong covariance along the first PC. Probably all three are independently important. It is speculated that diel migration by waterfowl may be responsible for the dispersal of plant propagules to the pond complex, whereas within-complex dispersal to establishment sites is enhanced by wind and water movement.