A study of succession on lowland heaths in Dorset, southern England: changes in vegetation and soil chemical properties.
Lowland heaths are high-profile ecosystems for conservation action in The UK, but they are under threat from invasion by Betula spp., Pinus sylvestris, Pteridium aquilinum, Rhododendron ponticum and Ulex europaeus. Ten heathland sites in the Poole Basin area of Dorset, where succession to one or other of the above species had occurred, were studied to examine the changes in vegetation and soil chemical properties. A series of hypotheses to explain vegetation successional trajectories, and soil chemical properties associated with vegetation change were tested using multivariate models (DECORANA - vegetation; CANOCO - vegetation and soil). A range of trajectories was found along which heathland communities move during succession, with some successional changes remaining closer to heathland than others. The Betula spp. succession caused the greatest changes in terms of the vegetation present. The Ulex europaeus and Pinus sylvestris trajectories retained some typical heathland species. Different soil nutrients were found to increase along different successional pathways, which were associated with the different successional species invading. Pinus sylvestris had similar soil nutrient concentrations to those of the heathland. Sodium concentrations increased during the Rhododendron ponticum succession. Concentrations of ammonium-nitrogen and nitrate/nitrite-nitrogen increased during the Pteridium aquilinum and Ulex europaeus succession. The Betula spp. had the greatest effect on the soil nutrients with increased pH, extractable phosphorus and exchangeable calcium. The results are discussed in relation to practical heathland management and the restoration of heathland after succession. Specifically, it is more sensible and cost-effective to restore heathland on sites where Pinus sylvestris successions have occurred, than where Betula spp. successions have occurred.