Changes in the Structure of Bryophytic Communities with the Progress of Succession on Sand-dunes

Reference is made to a previous paper discussing relationships between habitat conditions and the structure of bryophytic communities, as expressed by the application of a classification of growth-form in British terrestrial bryophytes. The effects of a changing habitat upon community structure are now considered by investigating the representation of certain growth-form types as succession proceeds on a sand-dune. The sequence of vegetation zones passing inland across the dunes is regarded as indicative of the stages in succession.The relative prevalence of the chief growth-form types is expressed semi-quantitatively by (a) a logarithmic transformation of frequency data for component species, and (b) a comparison of shoot-weights from a series of samples, with the following results:(1) Pioneer colonization of the mobile dunes is carried out mainly by species of a Short turf growth-form; to a lesser extent by representatives of the Mat form.(2) The latter reach their maximum in the fixed dune community, when Wefts enter and become prominent.(3) Wefts are predominant in the bryophytic community of the dune pasture.The growth-form of the chief species in each group is described in some detail, including reference to a degree of plasticity in the form adopted by Brachythecium albicans(a Mat-former). The relationships between the structure characteristic of the communities at each stage in succession and the prevailing environmental conditions are examined.Grateful acknowledgement is made to Mrs. E. T. Robertson for her help in the field and in the planning of this work.