Production and structure in the early stages of vegetation development in the Lauwerszee-polder

Summary In this study on vegetation development in the newly enclosed polder of the former Lauwerszee-estuary, data are presented on a qualitative and quantitative analysis of the pioneer vegetation of five experimental areas over the first four years. The methods used and the background to the study are briefly outlined. Data are given on structure, in terms of density and biomass, involving the speciesSalicornia spp., Suaeda maritima, Atriplex hastata andSpartina × townsendii and on soil factors (carbonate, organic matter, texture, K, P, total N, mineral N, pH and salt). Pattern and process in the pioneer stages are discussed, especially the underlying changes in environmental conditions and the behaviour of species in relation to these conditions. Only the halophytes mentioned could cope with the conditions of high salinity. It was found that in the initial phase plant densities are determined by the available amount of seeds, while after three years the total number and biomass is limited by environmental factors, especially those affecting soil-fertility. Thanks are due to Prof. Dr. D. Bakker for his stimulating and continuous interest in all stages of the present study and to Dr. A. J. Gray for critical reading and correcting of the English text. The project was realized by financial support of the Netherlands Organisation for the Advancement of Pure Research (Z.W.O.).