SUCCESSION FROM HEATHER MOORLAND TO BIRCH WOODLAND .3. SEED AVAILABILITY, GERMINATION AND EARLY GROWTH

(1) This paper examines seed input, germination and early growth of species found during the succession from heather moorland to mature birch woodland. (2) Numbers of seeds of Calluna vulgaris in the seed rain decreased rapidly with increasing age of birch stands. Large numbers of Calluna seeds were found, however, in soil beneath all ages of birch as well as the open moor, illustrating the longevity of seeds of this species. (3) Large numbers of Deschampsia flexuosa seeds arrived in the seed rain but very few germinated from the soil, indicating dependence on immediate seed regeneration, unlike Agrostis capillaris which had large, persistent soil seed stores. (4) The presence of seeds of Anthoxanthum odoratum, Agrostis capillaris and Rumex acetosella in seed rain and soil seed stores showed that the absence of these species from open moorland and young birch was not due to unavailability of propagules. (5) Germination of the species studied was apparently not affected by stand age, with the exception of Agrostis capillaris and Cerastium holosteoides which showed reduced germination on the open moor. Early growth of most species was faster, however, beneath the birch than on the open moor and improved beneath increasing ages of birch. (6) The natural regrowth of vegetation in the cleared plots was faster beneath the older birch than the young birch or the open moor. (7) The implications of differences in seed availability, germination and early growth are discussed in relation to observations and experiments on species changes beneath developing birch reported in the first two papers of this series.