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Gnèithean Ionnsaighaich

Invasive Species

Invasive species are species that are not native to an area and have usually been introduced by human activity. They often have few predators or competitors in their new environment, allowing populations to increase unchecked. As a result, they can upset local ecosystems, and become pest species which affect productivity.



Gunnera, commonly known as “Giant Rhubarb” is native to South America and was introduced to Harris as an ornamental garden plant in the 1980s. However, it has now become established as an invasive species, spreading out of gardens, onto neighbouring crofts and hill ground in some areas. Growing to a height of 2m and with its large leaves, Gunnera can shade out and out-compete native plants and can also cause problems by blocking drainage ditches and access tracks. The plant thrives in our mild wet climate and can spread rapidly.

Sustained efforts and control over the past few years has led to a significant decrease in Gunnera populations on the estate, but much work remains to be done.  Although Trust staff take the lead in dealing with this species, community volunteers have undertaken a great deal of the work.

In August 2017, Gunnera tinctoria was included on the list of species of European Union concern and is subject to EU Invasive Alien Species (IAS) Regulation (1143/2014). Strict restrictions apply to these species (subject to exemptions) so they cannot be imported, kept, bred, transported, sold, used or exchanged, allowed to reproduce, grown or cultivated, or released into the environment. Gunnera is not prohibited if it is already in your garden. However, you must act responsibly and not allow or encourage it to grow or spread outside your garden.


Control methods have included removing seed heads, digging up entire plants, and spraying plants using glyphosate-based pesticides.  If you would like to volunteer to help with the removal of this invasive species, please get in touch with us at 

For further information on Gunnera, please see:

North Harris Trust Gunnera Treatment Advice Leaflet

Piri-piri Burr
(Acaena novazelandiae)

Piri-piri Burr (Acaena novazelandiae) is currently found along paths and stream sides in the west of the estate. This is a low growing invasive species native to New Zealand that is thought to have originated through seeds brought over in wool imports. The burr which contains seeds is spread by walkers, dogs and livestock.

The species is out-competing native species in some areas and continues to spread well along paths in particular. We continue to monitor the extent of its distribution and are exploring means to control the species.

Piri-piri Burr

(Rhododendron ponticum)


Rhododendron was brought into the Western Isles as an ornamental plant for gardens. However, it is now considered one of the most dangerous invasive species in Scotland and the UK due to its ability to spread rapidly and outcompete native species. It is forbidden under Schedule 9 of the Wildlife and Countryside Act 1981 to plant rhododendron in the wild or to allow it to spread outside of your property.


While we do not currently have an active campaign of removal, we expect residents to make sure rhododendron plants do not spread outwith their properties, and we encourage people to favour other plants in their gardens.  For more information, see the Scottish Government page dedicated to the issue.

Prickly Heath
(Pernettya mucronate)

This South American plant is an evergreen low shrub with small, dark, shiny green leaves. It was introduced to North Harris in gardens as an ornamental plant, and if left unchecked can slowly spread onto heathland by outcompeting native heather species. 


We are actively monitoring the species and engaging in targeted removal where feasible.  Please report sightings to the North Harris Ranger Service 

Prickly Heath

Photograph sourced by NatureScot

(Erinaceus europaeus)


Hedgehogs are an invasive species in the Western Isles and threaten ground nesting birds.  While the hedgehog population in Harris is not thought to be large, they are present throughout the estate and more work needs to be done to determine their numbers and distribution.

A programme has been undertaken in Uist to capture hedgehogs and release them in their natural habitat on the mainland.

American Mink
(Neogale vison)

The non-native American mink is a great threat to ground nesting birds through predation of eggs, young or adult birds. On the Western Isles where most bird species nest on the ground, Mink can have a particularly devastating effect on local populations – tern and wader species are particularly susceptible. In North Harris mink predation also has a significant impact on wild salmon and upon crofters’ ability to keep hens successfully. The Hebridean Mink Project is an ambitious project working to eradicate mink from the entire archipelago of the Western Isles. Over 7000 traps (on average 3 traps per square km) have been dug in across Lewis and Harris with trap lines being set for one to two weeks at a time on a rotational basis.

American Mink

If you come across a mink trap, either set or un-set please leave it untouched where it is. Please report any sighting of minks to the North Harris Ranger Service at or directly to the Hebridean Mink Project via NatureScot.

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