SPECIES DYNAMICS AND NUTRIENT ACCUMULATION DURING EARLY PRIMARY SUCCESSION IN COASTAL SAND DUNES

1 The present study reports on a primary succession series which start ed on bare soil on the Dutch island of Schiermonnikoog after the build ing of a sand dike. Vegetational changes were studied for 18 years by means of permanent transects along a topographic gradient from a moist plain to dry dunes. Soil development and vegetation structure were re constructed using a chronosequence. A fertilizer experiment was set up in an intermediate successional stage in the plain and on the dune, i n order to determine which soil resources limited productivity. 2 Diff erences in salinity, flooding and moisture content were important dete rminants of the differences in species composition along the topograph ic gradient. In addition, year-to-year fluctuations of these factors s eem to be responsible for the year-to-year fluctuations in frequency o f occurrence of many short-lived species. These factors did not, howev er, show a consistent long-term trend over time. 3 From soil analyses and the nutrient addition experiment, it is concluded that nitrogen li mited above-ground biomass production. Over a period of about 16 years the total amount of nitrogen in the organic layer of the soil increas ed from 7 to 50 g N m-2 in the plains and from 1 to 15 g N m-2 on the dunes. 4 The accumulation of nitrogen during the successional series i s accompanied by an increased biomass, a decreased light penetration t o the soil surface, a decreased root/shoot ratio, increasing dominance of tall species, and a decreasing abundance of small, short-lived spe cies. These data suggest that the importance of light competition is i ncreasing during succession. 5 The importance of plant height versus l ight reduction at the soil surface in determining the outcome of light competition is discussed.