Variation in plant species composition in and adjacent to 64 ponds in SE Norwegian agricultural landscapes

Abstract

All vascular plants, classified by life and growth form into aquatic species (hydrophytes and helophytes) and terrestrial species of pond margins, were inventoried in 64 SE Norwegian agricultural landscape ponds and their adjacent margins for which also 56 explanatory variables were recorded. Gradients in species composition, found separately for aquatic and terrestrial species by parallel DCA and GNMDS ordinations, were interpreted by correlation and geostatistical analyses. The main gradients in species composition given by the first DCA ordination axes for aquatic and terrestrial species were strongly correlated, and both were related to water chemical and geographical variables. The second gradient in aquatic species composition was only weakly related to explanatory variables while for terrestrial species the second axis (like the first) was related to geographical, water chemical and some anthropological impact variables. The spatial structure of most explanatory variables was relatively weak, with a range of influence of 3–6 km. Species composition gradients and species richness variation of the investigated ponds and pond margins were thus to a large extent explained by the same variables. Like species richness, species composition was relatively weakly related to recorded explanatory variables. These two main characteristics of the investigated ecosystem thus both underpin the view that apparent randomness is important in this ecosystem and that ponds and their adjacent margins represent islands in the agricultural landscape that accumulate species more or less individualistically.