A reappraisal of cyclical processes in Calluna heath

Small-scale, short-term cycles constitute an important aspect of vegetation dynamics. It has been widely accepted that such cycles are characteristic of unmanaged heath communities where the dominant, Calluna vulgaris, undergoes an age-related series of changes in its growth and morphology. This is thought to give rise to a repetitive sequence of changes in the occupancy of gaps which form in the Calluna canopy and are first colonized by other species, with Calluna re-establishing later. Recently, doubts have been cast as to whether the changes are in fact often repetitive. A new study has shown much greater variability than was previously suspected in the transitions occurring in gaps. There is evidence that, in some instances though by no means all, Calluna can re-establish and thereby initiate a genuine cycle. It seems, however, that such re-entry is seldom by means of seedling establishment, but more frequently by development of adventitious shoots and roots on stems which have come to lie across the gap and have been covered by moss, moist litter or humus.