Individual study: A comparison of plant regeneration dynamics following gap creation at two geographically contrasting heaths, Cavenham Heath (Suffolk) and Thurston Common (Merseyside), England
Britton A.J., Carey P.D., Pakeman R.J. & Marrs R.H. (2000) A comparison of regeneration dynamics following gap creation at two geographically contrasting heathland sites. Journal of Applied Ecology, 37
Heather Calluna vulgaris-dominated heathlands are of high conservation priority in Europe. As an anthropogenic sub-climax plant community, they require regular management to prevent woodland succession and to maintain their conservation interest. Increasingly, Calluna is disappearing from lowland heathlands and being replaced by grasses, especially at sites in Western Europe. Calluna is highly competitive over much of its life cycle, but its competitive ability is reduced during the regeneration phase that follows the death of stands or that results from management activities.
In this study the influence of five factors (geographical location; dominant species i.e. heather or grasses; management techniques; gap size; and seed source availability) on regeneration of vegetation in gaps in two broadly similar lowland dry heaths over a 3-year period was examined.
Study areas: The experimental comparison of regeneration dynamics following gap creation was replicated at two geographically separate sites in the UK, to achieve a contrast of environmental factors, including climate. The two sites were chosen to keep vegetation and soil differences to a minimum: Cavenham Heath National Nature Reserve (NNR) in Suffolk, southeast England (Ordnance Survey grid reference TL 7572; 0°34'E, 52°19'N,); and Thurstaston Common Site of Special Scientific Interest (SSSI) in Merseyside, northwest England (Ordnance Survey grid reference SJ 2485; 3°8'W, 53°21'N). These two sites were both Calluna-dominated dry heaths on free-draining, acid, sandy soils.
Cavenham Heath (230 ha) comprises areas of birch Betula woodland, bracken Pteridium aquilinum, Calluna heath and acid grassland communities. It has a subcontinental climate with low rainfall (mean 548 mm/annum), hot summers (mean maximum July air temperature 21.7 °C) and cold dry winters (mean maximum January air temperature 5.8 °C). The area experiences high nitrogen input (35–80 kg N/ ha/year), mainly as dry deposition.
Thurstaston Common (75 ha) consists of birch woodland and Calluna-dominated heath. It has a typical Atlantic climate of a site close to the west coast of Britain. It experiences moderate rainfall throughout the year (mean annual rainfall 720 mm) with warm summers (mean maximum air temperature in July 20.3 °C) and mild winters (mean maximum air temperature in January 7.1 °C). Nitrogen deposition levels are relatively low, around 10–15 kg N/ha/year, occurring primarily as wet deposition.
Experimental design: The influence of geographical location, vegetation type, gap size, management type and seed addition, on vegetation regeneration following gap creation was investigated. At Cavenham, this was done on two vegetation types, Calluna heath and hair-grass Deschampsia-dominated grassland; at Thurstaston only Calluna heath was present and a single set of experimental plots was established. Similar mature Calluna stands were selected at both sites. The experiment thus comprised three 'blocks': Cavenham-Calluna, Cavenham-Deschampsia and Thurstaston-Calluna, within which the treatments, management, gap size and seeding, were nested.
A fully factorial design was used, with three management types used to create gaps (cut, turf-stripped and rotavated), three gap sizes (1 m², 0.25 m² and 0.0625 m² square plots) and seeded and unseeded plots. In the cutting treatment the sward was clipped down to soil level and the plant material removed. In rotavated plots the sward was clipped to ground level and roughly chopped. The top 15 cm of the soil was then inverted and broken up with a spade, and the chopped plant material mixed in. For the turf-stripping treatment, the sward and underlying organic matter were removed to a depth of about 10 cm, exposing the sandy subsoil. The seeding treatment was reciprocal i.e. Calluna seed was added to gaps in Deschampsia vegetation and vice versa. Native seed of both species was obtained from a commercial supplier. Sowing rates of 35,000 seeds/m² for Calluna and 20,000 for Deschampsia were used (calculated to be approximately equivalent to 1 year of seed rain at these sites). Plots were spread randomly within the designated vegetation types. There were three replicates of each treatment combination within each block.
Monitoring: The experiment was set up in March 1996 and subsequent regeneration monitoring was undertaken twice yearly at the beginning and end of the growing season (approximately April and October). A 5 × 5 cm cell grid was placed over each gap and the species present in each square noted in four categories: Calluna, Deschampsia, other species and bare ground.
The 'other species' typically included birch, sand sedge Carex arenaria, red fescue Festuca rubra, bedstraw Galium sp. and sheep's sorrel Rumex acetosella at Cavenham, and birch., hawkweed Hieracium sp., Scots pine Pinus sylvestris, bracken and gorse Ulex sp. at Thurstaston. Results were expressed as the percentage of the total cell number occupied by each species group.
Site location had the greatest effect on patterns of vegetation regeneration. Regeneration at Thurston Common (north-west England) was faster and more dominated by Calluna than regeneration at Cavenham Heath (south-east England), which was dominated by other plant species including many grasses and annuals. Addition of Calluna seed at the Breckland site failed to increase its cover. It was concluded that climatic (e.g. drier conditions) or other environmental factors were the probable cause of poor heather regeneration in Breckland.
Grass cover in regenerating areas was greatest at Cavenham, with Deschampsia establishing in all gaps where there was a seed source (either from surrounding vegetation or applied as a treatment). At Thurston, Deschampsia establishment was limited, even where seed was applied.
Conclusions: In view of the differences shown between the regeneration dynamics of these two contrasting sites in this study, this has implications for the conservation management of heathlands, which tends to follow a similar prescription throughout the UK. It is suggested that management regimes should be tailored to suit the conditions at individual sites as regeneration dynamics may be extremely variable.
Note: If using or referring to this published study, please read and quote the original paper. The original paper can be viewed at: http://www.blackwell-synergy.com/doi/full/10.1046/j.1365-2664.2000.00533.x