Emergent wetland vegetation data recording: Does an optimal period exist?

Aims Certain parts of the growing season have been proposed as optimal for recording relevant releves of forests and dry grasslands and so the monitoring of these vegetation types has become more time- and cost-effective. We investigated whether it is possible to propose an optimal period during the year for making relevant releves of emergent wetland vegetation. Location Marshlands of the central Balkan Peninsula. Methods One hundred and eighty-five permanent vegetation plots were investigated in three distinct time periods: spring, summer and autumn. In order to identify the communities, cluster analyses were carried out, and diagnostic species for each cluster were determined. The potential for temporal change of the communities regarding the species and life form composition was assessed using PERMANOVA and NMDS analyses. The Friedman test was used to assess the significance of seasonal change in the communities regarding their species richness, recordability and Shannon diversity. Results The level of floristic similarity among the 11 phytocoenoses analyzed significantly varied over the growing season while the composition in terms of their diagnostic species remained unchanged. The majority of the communities showed statistically significant seasonal changes in the qualitative and quantitative characteristics of the vegetation, life form composition and cover. Although different communities expressed significant modifications in these parameters between different pairs of seasons, all of them showed changes in the mentioned parameters between spring and autumn. The degree of intra-annual variation in the species richness, species recordability and Shannon diversity was low in almost all phytocoenoses. Conclusions Summer is the optimal period for recording most of the species from the total list of the communities developed on hydrologically stable habitats, while spring is more appropriate for making releves on periodically inundated habitats. The sampling time has negligible impact on the classification of associations but it could have important implications for the classification of higher-ranked syntaxonomic units of the class Phragmito-Magnocaricetea.