Individual study: Regeneration of heather Calluna vulgaris of different ages under spring or autumn cutting and burning regimes, Kerloch Moor, Aberdeenshire, Scotland
Miller G.R. & Miles J. (1970) Regeneration of heather (Calluna vulgaris (L.) Hull) at different ages and seasons in north-east Scotland. Journal of Applied Ecology, 7, 51-60
On upland grazing land in Britain, burning of old heather Calluna vulgaris has been traditionally undertaken to increase young growth as food for red grouse Lagopus lagopus scoticus, red deer Cervus elaphus and domestic sheep. The aim is to burn patches in rotation so that heather is renewed every 10-20 years. However, this may be difficult to achieve because of adverse weather, labour shortages and a law that limits the length of the burning season. Hence, as an alternative to burning, some landowners have recently begun to cut heather using rotary cutters. This present study investigated regeneration of heather stems aged from 2-3 to 34-37 years old to, determine the age when vegetative regeneration was most rapid after burning or cutting and to assess if there was any difference between regeneration according to season of management.
Study area: The study was undertaken on a 65 ha block of Kerloch Moor (120-220 m a.s.1.) in Aberdeenshire, north-east Scotland. Vegetation was dominated by heather (average cover c.75%), two other ericaceous shrubs bell heather Erica cinerea and cross-leaved heath E.tetralix were frequent (c.5% cover each). Mat-grass Nardus stricta and deer sedge Trichophorum caespitosum) were locally abundant in small patches. The vegetation was grazed by rabbits Oryctolagus cuniculus, mountain hares Lepus timidus and red grouse, but fences excluded cattle and sheep.
About one-third of the area had been burned in 77 patches (varying from a few square metres to 1.5 ha) between autumn 1961 and spring 1965, over a mosaic of heather stands of different ages.
Regeneration after fire: Heather canopy age at the time of burning was determined by counting annual rings of stems of each burnt patch; 99 stands, aged 3-37 years before burning, were recognized. Each was allotted an age-class (6-10, 11-15, 16-20, 21-25 and 26-30 years) and two stands that had been burned in the spring of each of the years 1962-65, and in the autumn of 1964, were selected. In each stand the vegetation in 10, 0.1 m² random quadrats of was clipped at ground level. Heather was separated from other species, dried and weighed.
The proportion of ground covered by heather was also estimated by eye to the nearest 10% within 10, 0.1 m² random quadrats in each of 35 different stands burnt between autumn 1963 and spring 1965. The data were placed in five age-classes as above. Differences in heather regeneration between autumn and spring burns were analysed.
Regeneration after cutting: Six almost pure stands of heather, aged 2-3,6-8, 12-14, 16-18,21-24 and 34-37 years, were selected and fenced against rabbits and hares. In October 1964 the vegetation was cropped in nine 0.25 m² random plots in each stand, with a second set cropped in April 1965. Litter was raked off after cropping, and surrounding vegetation cut back to prevent shading of the plots. In October 1965 regeneration was assessed by: the number of sprouting centres (i.e. points from which groups of heather shoots arose on cut stems) in each plot; and harvesting plots, and drying and weighing the heather to assess above-ground biomass.
The density of old stems was estimated from counts in 10, 0.1 m² quadrats within each stand. A comparative measure of soil water content (% oven-dry weight of soil) was obtained from three, 10 cm deep cores in each plot. The surface layer thickness of soil organic matter was measured at each plot centre. The relation between these three variables and the dry weight of regenerated heather was examined.
Age and density of heather stems: Thirty heather stands, aged from 2 to 28 years, were sampled to determine the relationship between heather age and stem density. Ten 0.1 m² quadrats were placed at random in each stand, the heather cropped to ground level and stems counted.
Heather regeneration was most satisfactory in 6-10 year old plants and regeneration progressively declined thereafter with increasing age of stands. Within older plants, there was a decrease in the number of centres from which new sprouts arose.
Regeneration was more prolific after burning in autumn than in spring, contrary to the traditionally held belief. In contrast, regeneration was more prolific after cutting in spring than after cutting in autumn.
The authors indicate that there are practical considerations which make it difficult to use cutting as a tool to encourage heather regeneration, but on suitable sites a combination of cutting and burning might be useful. In general burning or cutting every 11-15 years is probably appropriate, but this will depend on local factors such as the heather status, climate, soil and grazing pressure.