PLANT COEXISTENCE IN COASTAL HEATHS - HABITAT SEGREGATION IN THE POSTFIRE ENVIRONMENT

Previous studies of heaths on Pleistocene coastal sands showed consist ent variation in patterns of floristic composition between areas on ri dges and slopes but not within them. A large wild-fire that swept this system provided an opportunity to observe temporal processes in habit at segregation of species. Ridges and slopes were found to differ in s pecies richness of seedlings in 0.0625 m(2) quadrats and there was no evidence that the species richness in the two habitats was converging over 3 years. This suggests that initially these processes differ in s pace between the two habitats with more species in the wet heath being packed into a smaller area than in the dry heath. Seed-banks of speci es did not saturate available space for recruitment in either habitat, but seedling densities differed asymmetrically between habitats acros s two pairs of species studied. Experimental manipulation of seeds amo ng habitats also showed distinct differences in establishment and surv ival among representative species from different habitats. The presenc e of seed-banks of wet-heath species in dry heath suggested that recru itment of their seedlings may occur there, but experiments showed that seedlings that arise from them do not survive there. Conversely, alth ough no seed-bank of either dry-heath species studied was found in wet heath, our manipulations showed that their seedlings could grow there . Thus, superficially, physiological tolerance appeared to limit regen eration of wet-heath species in dry heath. However, there appeared to be no physiological limit for dry-heath plants to survive in wet heath . This paper shows that segregation of species may operate at either o f two stages of the life cycle: at dispersal when safe sites for estab lishment are required, and at recruitment after seedlings have establi shed. These findings highlight the importance of the regeneration nich e in structuring community composition in coastal heaths, and contrast with traditional explanations of species segregation invoking physiol ogical tolerance and competition at later life-history stages.