1 Primary succession on coastal sand dunes has generally been presumed to b
e driven by autogenic environmental change associated with dune stabilizati
on and gradual soil development.
2 An extensive chronosequence of dune-capped beach ridges is found adjacent
to northern Lake Michigan and the youngest 13 ridges (aged 30-440 years ol
d) show a clear pattern of primary succession and development of a forest e
3 Seed-addition and seedling-transplant experiments indicated that coloniza
tion of young sand dunes by late-successional Pinus and Quercus species is
constrained by limited seed dispersal, seed and seedling desiccation, and s
eed predation rather than seedling success being constrained by low soil ni
trogen availability. Their establishment may therefore depend on coincidenc
e of chance seed dispersal, favourable weather conditions and low rodent de
4 In addition, episodic burial by sand prevents most species from colonizin
g young dune ridges, while burial of seedlings by litter limits recruitment
on older dune ridges with developing forest. The intensity of competition
increases during succession.
5 Dune succession is better described as the transient dynamics of coloniza
tion and competitive displacement rather than the result of gradual soil de
velopment and competitive displacement.