Environmental and spatial processes structuring macrophyte metacommunities in restored pondscapes

Pond network creation can enhance freshwater biodiversity. However, environmental and spatial processes that structure macrophytes, a group central to pond ecology, need to be understood to improve pondscape design. Here, macrophyte communities were surveyed and environmental and spatial data were collected in two networks of man-made permanent ponds in western and northeastern Europe. Macrophyte diversity was high in the pond network in Latvia, and the relative cover of emergent, anchored submerged, anchored floating leaved and free-floating species varied among ponds. Diversity in the network on the French-German border in the former Rhine floodplain was low and consisted mainly of emergent plants and charophytes. The low diversity on the French-German site may result from the presence of the invasive calico crayfish (Faxonius immunis). Environmental variables, including water transparency, pH, chlorophyll-a concentration, as well as shade from surrounding trees and calico crayfish abundance (French-German site only), were correlated with abundances of macrophyte taxa. The variables were also correlated with macrophyte community metrics, including total macrophyte cover, taxonomic distinctness and the relative cover of submerged, emergent and free-floating life forms. Pond surface area and isolation had low contributions to the correlation between environmental variables and macrophyte community metrics. For the Latvian site only, macrophyte community similarity declined with geographic distance between ponds, but more importantly with differences in shade from surrounding trees and water transparency. A design of ponds with diverse environmental conditions and surroundings, as well as groups of ponds providing similar habitats, may be most effective for enhancement of macrophyte diversity at the pondscape scale.