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- Materials and methods
1. Lowland heaths are high-profile ecosystems for conservation action in Britain, but many areas have been invaded by Betula spp., Pinus sylvestris, Pteridium aquilinum and Rhododendron ponticum. As succession occurs on heaths, changes occur in both the vegetation and the soil chemical properties of the site.
2. Nine heathland sites in the Poole Basin area of Dorset were studied, where management of successional sites to restore heathland had occurred. The efficacy of heathland restoration in terms of both the vegetation and the soil chemical properties was assessed.
3. The management had allowed many heathland species to establish and the majority of sites to start to become similar to the neighbouring heathland. The reversion of increased soil nutrients was found to be more problematic, with levels of ammonium–nitrogen, phosphorus, pH, calcium and magnesium remaining greater than those of the heathland soils.
4. The vegetation and soil data were analysed using canoco (canonical correspondence analysis) and were then used to test four hypothetical models that related changes in biotic factors (vegetation) and abiotic variables (soil nutrients) following management to the success of the restoration of heathland on successional sites.
5. A second canoco analysis was carried out in which the managed sites were treated as passive samples. This model was used to measure the distances between the heath, successional and managed sites. These distances provided measures of management success and the resilience of the treated late-successional ecosystem.
6. The successional species present before management affected the success of reversion; management of Pinus sylvestris sites was generally more successful than management of others sites, especially those invaded by Betula. The most significant effect of different management techniques resulted from litter-stripping, which reduced the nutrients available and improved and accelerated the success of reversion.
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- Materials and methods
Dorset heaths have declined dramatically in area, diversity and structure over the last century (Chapman, Clarke & Webb 1989; Webb 1990). One cause of these losses has been an increase in scrub invasion and succession to woodland (Webb 1990) because of a decline in management practices that inhibit the succession of heath to woodland.
As succession occurs on heathland, the species composition of the site changes (Miles 1981; Mitchell et al. 1997). However, management to reverse succession and restore heathland is usually targeted at a few species, i.e. the major invasive species, which on the Dorset heaths are Betula spp., Pinus sylvestris (L.), Pteridium aquilinum (L. Kuhn) and Rhododendron ponticum (L.). The ability of the invaders to recover or persist after management, i.e. the resilience of the successional stage, will influence the success of conservation management to restore heathland.
Heathlands are generally found on nutrient-poor and infertile soils (Gimingham 1992). As succession occurs soil chemical properties change (Miles 1981, 1985; Mitchell et al. 1997). The greatest changes occur when Betula spp. invade, resulting in increased pH, exchangeable calcium and extractable phosphorus (Miles 1981; Mitchell et al. 1997). Increased concentrations of other soil nutrients are associated with different successional trajectories; extractable ammonium–nitrogen, nitrate/nitrite–nitrogen and exchangeable potassium increased with Pteridium aquilinum and Ulex europaeus (L.) successions, sodium increased with Rhododendron ponticum succession, and organic matter increased with Pinus sylvestris succession on Dorset heaths (Mitchell et al. 1997).
If restoration is to be successful then management to restore heathland must reverse the changes in both vegetation and soil nutrients. There are four hypothetical models that may describe the response of a site to management: (i) good restoration with the managed site indistinguishable from the target; (ii) poor restoration with the managed site remaining close to the ‘start’ site; (iii) partial restoration; and (iv) movement to a different endpoint. This paper describes the study of the efficacy of restoring heathland communities on land where succession had occurred and the ‘starting’ communities were dominated by one of the following species: Betula spp., Pinus sylvestris, Pteridium aquilinum or Rhododendron ponticum. The aims were to answer the following questions.
1. Was management effective in restoring heathland communities and preventing the recovery of late-successional communities?
2. Was management effective in reducing any soil properties that are known to be greater in the late-successional communities?
3. Was it possible to measure the success of management and the resilience of the managed site?
4. Does the species of invasive plant present before management, method of management or the length of time (years) since management affect the success of the restoration?
An attempt was made to answer these questions by contrasting a range of sites where late-successional communities were managed by the Royal Society for the Protection of Birds (RSPB) to restore heathland (‘managed’ sites), with areas where heathland communities were still present (‘target’ communities) and where the successional species were still present (‘start’ communities). An assumption was made that the start community and the managed communities were similar before management was applied.