Salt marsh vegetation: Latitudinal gradients in the zonation patterns.

Zonation patterns of salt marsh vegetation were examined at latitudes ranging from 44°40'N at Halifax, Nova Scotia, to 58°50'N at Churchill, Manitoba. It was found that in all areas examined the landward boundaries of the species' zones were more nearly coincident (i.e., more clustered) than their seaward boundaries. A conspicuous latitudinal trend was found: the clustering of both landward and seaward boundaries increased with increasing latitude. Evidence that between-species competition influences the locations of zone boundaries was also obtained. Possible implications of the results in terms of a relationship between intrapopulation polymorphism and latitude are discussed.