The Scottish Invasive Species Initiative plant control project focuses on tackling four key target species across our project area - these are the worst offending plants that cause significant problems and are found throughout much of Scotland.
Most of these target invasive species are known for growing alongside watercourses, on burn sides and riverbanks. These plants produce large numbers of seeds every year, which are spread by humans, by wind and by water, or have stubborn rhizomes (roots). Seeds or plant/root fragments spreading down the river is a frequent problem and new populations of plants are often found downstream of original growing sites.
To be effective, plant control needs to work at a catchment scale (the main river and all the small rivers and burns that feed into it) so all the plants are removed and there is nothing left to re-infest rivers downstream. However, this can be challenging as it requires several landowners to work together to clear a river of plants along its length. Working with local fishery trusts, volunteers and land managers we are achieving this by co-ordinating action and undertaking significant removal works to get invasive plant populations into a maintenance state.
Click on our key target plant species to read more about each invasive species and how we are managing them:
Invasive plant management
The first step in plant control is establishing what is there, and where did it come from. Locating the source of the plant is important, and ideally strategic control works start there and progress downstream.
Some of our rivers had already been surveyed in the past and control works started - while in others we started from scratch and undertook survey work to establish where plants were present before initiating control and management.
Most plants are treated using one of two methods;
Treatment with herbicide – this is the most effective way for treating; Giant hogweed, Japanese knotweed, American skunk cabbage and White butterbur.
We use either a spot spraying method, where a minimal amount of herbicide (Glyphosate) is applied directly to the leaves of the plant, or stem injection. Qualified personnel (or those under immediate supervision of a qualified person) carry out this work.
- Hand digging / pulling – Himalayan balsam has a small shallow root system and it can easily be pulled from the ground by hand. However, hand removal is more time consuming, but as they say, many hands make light work!
Some other species can be dug out when the plants are small e.g. Skunk cabbage.
In cases where invasive plants growing at 'dominant' and 'abundant' densities (defined using the DAFOR scale) or where access is deemed difficult, treatment is being carried out by professional contractors as well as our project staff, sometimes supported by volunteers. These populations will be reduced in size and density to a low maintenance state which can then be managed and maintained by volunteers after our project finishes.
Trying something different
We are also doing some more experimental control of invasive plants; trialling the clearance of giant hogweed using sheep in the River Deveron catchment and trialling different methods of control and habitat restoration of White butterbur on the River Spey.
Read more about these case studies
It is nearly always the case that these invasive plants will grow back for several years after initial removal or control - as plants will have been missed or not killed by previous treatments, seeds from the plant will already be in the soil ready to germinate or the plant may have a tubular root system which persists underground.
Permanent removal of plants from a site is likely to require re-visiting the same site for a number of years and so takes dedication. Miss a year and you’ll be back to square one! This is why our project is establishing plant control at a local level, within communities who can adopt and maintain sites invasive free for years to come. We are doing this by training local people in techniques like pesticide application and supporting them in setting up local groups and networks.
Every year we undertake monitoring work, re-surveying sites after work has been undertaken to see how successful control work has been and identifying priority sites for the next year.
On sites where large areas of invasive plants have been removed (particularly the case with White butterbur) what is left will be areas of bare, open ground. Given time, these areas will naturally regenerate with native flowers and grasses, but depending on the site, waiting years may not be an option. Riverside sites would be at risk of erosion if there is no vegetation to stabilise the soil and large bare areas would look visually unattractive and may have local biodiversity impacts.
Where it is an option we are trying a few different methods of habitat restorations works on some sites, including planting native trees and shrubs and planting native wildflower seed.
How can you help?
We need volunteers to get involved in all aspects of our plant control project; surveying and recording distributions, applying pesticide (we can provide free training and equipment), conservation volunteer days to remove plants and undertake habitat restoration works, and reporting invasive plant sightings.
Find out more about Volunteering
Find out more about invasive non-native plants;
What should I do if I have an invasive plant in my garden