Invasive non-native species 

On the River Dee we have 4 main invasive non-native plant species – giant hogweed, American skunk cabbage, Himalayan balsam and Japanese knotweed, and one mammal – American mink.

The plants were brought to the UK from their native ranges in the early 1800’s; mainly as decorative garden plants. It wasn’t long before we realised how easily they spread in the wild and along watercourses, but it was a number of years before their negative impacts became obvious. 

As these plants often grow quickly in large, dense patches, they overshadow native species causing a reduction in biodiversity on our riverbanks. This, in turn, increases erosion of riverbanks and siltation of the waterways so when the plants die back in autumn very few plants and root systems are left to bind the soil. Himalayan balsam is also very attractive to insects often to the detriment of native plants further impacting our biodiversity. 

Further to the environmental impacts, invasive non-native plants can limit our access to riparian areas for recreational uses such as fishing and walking. In most cases this is only due to the dense stands and difficulty of access, but giant hogweed contains a phytotoxic sap that reacts with the sun when in contact with skin and can cause serious burns.

The River Dee Trust controls invasive plants along the River Dee and River Don. For most plants control is by herbicide spraying but Himalayan balsam is hand pulled where possible and strimmed in the larger, easily accessible patches. 

To identify the invasive plants that grow on the Dee Catchment click here – https://www.invasivespecies.scot/invasive-plant-project

American mink were farmed for their fur in the UK from 1920 until being completely banned in 2000.  Between deliberate releases and escapes there have been populations of American mink breeding in the wild in the UK since the 50’s.

Mink are prolific hunters and have had drastic impacts on ground nesting birds and small mammals. Water voles are a particular favourite and the decline in their numbers is thought to be almost fully down to predation by American mink.

A network of over 80 mink rafts throughout the Dee and Don catchments use clay pads to monitor for the presence of mink. Live traps and humane dispatch are then used to reduce their numbers on our rivers.

The River Dee Trust is a partner of the Scottish Invasive Species Initiative which is a five-year partnership project in northern Scotland led by NatureScot and involving many fishery boards and trusts and the University of Aberdeen. The project is funded by the Scottish Government’s Nature Restoration Fund, managed by NatureScot.

None of our control efforts would be possible without our army of volunteers who give up their time to help spray plants, monitor a mink raft or just report their sightings of our target species. This can be done via the reporting tools on the SISI website – https://www.invasivespecies.scot/index.php/report-american-mink-sighting

https://www.invasivespecies.scot/report-invasive-plant-sighting

If you would like to join us in our control efforts, please contact our Invasive Species Officer at jan@riverdee.org.