Competition and niche separation in Sphagnum

In bogs in eastern Sweden there are usually three, four, or five species of Sphagnum occurring along the gradient from hummock to hollow in the order S. fuscum, S. rubellum, S. balticum, S. tenellum, and S. cuspidatum. Transect studies revealed that, in some cases, the distribution of the species along the gradient was affected by the species composition in the transect. These cases were interpreted as niche shifts, indicating that some species are replaced at their lower limit by a superior competitor. Results from field experiments, in which the species were grown in different combinations at different heights above the water table, were not always in agreement with the transect studies. For example, the experiments gave only partial evidence of S. rubellum replacing S. fuscum and no evidence of S. tenellum replacing S. balticum. In these cases, priority of colonization may be more important than competition.