Species dynamics and nutrient accumulation during early primary succession in coastal sand dunes

1. The present study reports on a primary succession series which started on bare soil on the Dutch island of Schiermonnikoog after the building 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 reconstructed using a chronosequence. A fertilizer experiment was set up in an intermediate successional stage in the plain and on the dune, in order to determine which soil resources limited productivity. 2. Differences in salinity, flooding and moisture content were important determinants of the differences in species composition along the topographic gradient. In addition, year-to-year fluctuations of these factors seem to be responsible for the year-to-year fluctuations in frequency of occurrence of many short-lived species. These factors did not, however, show a consistent long-term trend over time. 3. From soil analyses and the nutrient addition experiment, it is concluded that nitrogen limited above-ground biomass production. Over a period of about 16 years the total amount of nitrogen in the organic layer of the soil increased 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 is accompanied by an increased biomass, a decreased light penetration to the soil surface, a decreased root/shoot ratio, increasing dominance of tall species, and a decreasing abundance of small, short-lived species. These data suggest that the importance of light competition is increasing during succession. 5. The importance of plant height versus light reduction at the soil surface in determining the outcome of light competition is discussed.