Regeneration by Natural Layering of Heather (Calluna vulgaris): Frequency and Characteristics in Upland Britain

Abstract

1. Heather, Calluna vulgaris, can regenerate by layering (adventitious rooting) of stems. The frequency of layering stems, and strength of adventitious rooting, was surveyed in 11 stands (of 0.5-2 ha each) at eight sites dispersed over the drier, eastern half of the northern British uplands at altitudes of 300-400 m. Associated topographic, stem and stand structure characteristics were recorded, together with the composition of the litter and moss layer surrounding the stems. 2. Some adventitious roots were observed in over 50% of stems in all stands, and in 90% of stems in six stands. Strongly developed adventitious root systems were present on more than 30% of stems in seven of the stands. 3. Stem prostrateness and deeper humus-rich or peaty soil horizons were consistently associated with layering. Layering was associated with the absence or low abundance of Hypnum cupressiforme/jutlandicum and lichens (mainly Cladonia spp.). There was weak evidence that it may have been associated with the presence of Sphagnum spp., Leucobryum glaucum and pleurocarpous mosses other than Hypnum. More layering was observed in stands of younger mean age. Stands with strongly developed layering were more sheltered. 4. Strongly developed layering was associated with increased stem and canopy vigour distal to the point of rooting, and in some cases atrophy of the remaining part of the stem. This may lead to the in-filling of canopy gaps and to a reduction in the occurrence of conditions suitable for further layering. Continuity of layering and stability of Calluna cover is likely to require discontinuous Calluna cover. 5. The importance of layering has been underestimated in previous studies of Calluna dynamics which have focused mainly on stands burnt on regular, comparatively short rotations. This gap in understanding has management implications, particularly in upland Britain. Extensive areas of Calluna heathland in upland Britain are burnt infrequently, although the accepted ideal among moor managers is to burn regularly on 10-15 year rotations. We question this management dogma