Natural Connections: ‘A top-down’ catchment-based approach to invasive plant control on Dartmoor
There are a number of invasive non-native plant species that occur on Dartmoor, of which we think two species, Himalayan Balsam and Skunk Cabbage are having the most significant environmental impact. Both species are highly invasive, posing a real threat to the native flora and important habitats on Dartmoor. Himalayan Balsam is now covering whole fields, the banks of streams, floodplains, and is also now even appearing on the open moor. The dense tall thickets have a major impact on nature conservation, archaeology, access and landscape value and in the winter leave behind bare ground at risk of erosion. Skunk Cabbage is more localised in its distribution, but is now starting to become an issue, particularly along watercourses from high up in the Bovey catchment.
There is a growing recognition that if something isn’t done soon on Dartmoor, the problem has the potential to increase rapidly. At the same time, Dartmoor is the top of the catchment for most of Devon’s rivers; therefore there is the opportunity to start eradicating the plants from the source of the original introduction and work methodically downstream. The control of Himalayan Balsam, and other invasive plant species, has been one of the work areas of the Moor than meets the eye Heritage Lottery Funded Landscape Partnership scheme. The MTMTE project is focusing on the wet grassland (rhôs) and wet woodland habitats which form an extensive network of wildlife-rich habitat in valley systems at the top of the Dart and Bovey catchments.
Whilst it is recognised that the problem is far wider than the MTMTE project area, an integrated and coordinated control project has being piloted at the top of the Bovey catchment, targeting both Himalayan Balsam and Skunk Cabbage. The approach has been to work with local landowners and tenants, rangers, volunteers, and voluntary wardens. The top of each tributary in the upper Bovey catchment was surveyed in 2015 and 2016 for American skunk cabbage and Himalayan balsam to establish the source of the problem. For American skunk cabbage targeted eradication work involved different methods appropriate to each area and trialled during 2016 and 2017 at the most effective time of year (March to July). During 2017 the effectiveness of various treatment measures have been monitored to compare mechanical methods (hand digging, removing seed heads, cutting) and herbicide application under an Environment Agency licence. North Bovey Conservation Group and Natural England’s Ecoskills Conservation trainees have also been actively engaged in assisting with treatment and advising landowners. Monitoring suggests any treatment is better than none, with varying degrees of effectiveness between mechanical and chemical treatment. So far chemical treatment is proving to be the most successful method in kerbing growth, however eradication is a way off and is likely to take a number of seasons. By focussing on the ‘top of catchment’ approach the project has been able to successfully tackle invasive species at source whilst engaging with landowners, volunteers and closely monitoring the effectiveness of different treatment measures. The pilot comes to an end in 2017 however, treatment will continue with those landowners and volunteers already engaged and it is hoped community engagement will continue through existing groups. MTMTE and Dartmoor National Park Authority aims to develop a project linked to other initiatives and citizen science projects and expand the control of these invasive plants at prioritised locations where they threaten important habitats elsewhere on Dartmoor.