About 52ha of the Park – over 25% of the area of dry land – was densely infested with non-native species of shrubs at the start of the program.
Since then over 7,250 Peking cotoneaster (Cotoneaster acutifolius) and Tartarian honeysuckle (Lonicera tatarica) have been removed and countless European mountain ash (Sorbus aucuparia) seedlings pulled up. Monitoring of weeded areas in the floodplain over the last 4 years shows native vegetation to be recovering well and filling in the gaps left by removing these species (details here). Monitoring of recovery along the escarpments is planned for the next 4 years.
Every year volunteers have removed flowers and seeds from species such as yellow clematis and creeping bellflower that cannot be simply dug up as the roots are too deep or break and regrow. So far this seems to have prevented these species spreading, and no new colonies have established since the Program started. It is hoped that in the future a more permanent method of control will be found.
We track changes in the distribution and density of the different invasive plants using GoogleEarth. An example of the change in the distribution and abundance of cotoneaster since the start of the Program is shown below:
Other species that cannot be removed manually such as common buckthorn (Rhamnus cathartica) or European barberry (Berberis vulgaris) have been treated with herbicide or, in the case of leafy spurge (Euphorbia esula) – an extremely invasive herbaceous species – with a bio-control agent.