Observations on the colonization of a young polder area in the netherlands with special reference to the clonal expansion ofPhragmites australis

In 1968, the polder Zuidelijk Flevoland was reclaimed in the Netherlands. Observations on species succession were made during a period of seven years in an area later known as the nature reserve Oostvaardersplassen. Directly after reclamation, a large number of plant species were recruited. Here, only the dynamics of the three dominant species will be discussed, i.e. the annual mudflat speciesSenecio congestus, and the long-lived emergent macrophytesTypha latifolia andPhragmites australis. Small differences in elevation had a large impact on seedling recruitment. Overall,S. congestus dominated in the first year after reclamation, andT. latifolia prevailed during the second and third year. Thereafter,P. australis became dominant, despite fewer seedlings. In the first three years after reclamation, clones ofP. australis grew very slowly, afterwards they showed a constant expansion rate of ca. 4 m/yr. However, close to pools waterfowl grazing slowed down the expansion of clones. The observed spatial and temporal variation in the colonization of this young polder area can be explained by species differences in life history traits, resource capture, as well as in the susceptibility to stem-boring insects and waterfowl grazing.