Present and future population dynamics of Prunus serotina in forests in its introduced range

Prunus serotina, a North American tree species, is considered one of the 100 worst invaders in Europe. Although an increasing number of studies has focused on P. serotina in Europe, several aspects of the species have remained unstudied. Moreover, most studies focused on heavily invaded areas. We wanted to gain insight into the radial growth and the spatiotemporal variation in the regeneration of P. serotina in forest understories, the patterns of long-term spontaneous P. serotina colonization in areas where the species had not been introduced intentionally, and long-term forest development with P. serotina. Prunus serotina growth and regeneration were studied in seven Pinus sylvestris stands in Flanders. Growth was reduced by 50 % compared to growth in full light conditions and was related to tree age and diameter and competition with neighbouring trees. The seedling bank with high densities of seedlings smaller than 20 cm and up to 6 years old stabilized the erratic early regeneration of P. serotina. We also reconstructed the P. serotina invasion for a pine forest in the Netherlands and a deciduous forest in Flanders that had not been managed for over 60 years and were located in areas with an initially low propagule pressure of P. serotina. Long-distance dispersal events and windows of opportunity triggered the P. serotina invasion. Further colonization was directed by connectivity to seed sources and light availability. The presence of native shrub species, dense herb layers, and quick canopy closure seemed to hamper further P. serotina establishment while high herbivore densities may have favoured P. serotina over native species such as Quercus robur. We used the model SORTIE-ND to simulate 500 years of forest development for a pine forest with P. serotina. The output suggested that if Q. robur was able to regenerate, the longer lifespan of Q. robur may enable the species to become dominant over P. serotina. With this thesis, we demonstrated that the invasiveness of a species depends on the characteristics of the invaded ecosystem and that models of forest development such as SORTIE-ND can be useful to simulate the future role of invasive tree species in forests