Invasive non-native species in woodlands

The term ‘invasive species’ refers to non-native plants and animals introduced into wild habitats either deliberately or inadvertently. These species are often able to proliferate rapidly by outcompeting native species that occupy similar ecological niches. They often cause significant economic damage.

Invasive plants in Welsh woodlands

Some of the Invasive plants that may cause problems in Welsh woodlands include:

• Japanese knotweed (Fallopia japonica)
• Himalayan balsam (Impatiens glandulifera)
• Rhododendron (Rhododendron ponticum)

These plants are a threat to native flora and habitats. They are aggressive and form dense stands that exclude other plants.

Invasive animal species

Some of the invasive animal species in Welsh woodlands include:

• Grey squirrels (Sciurus carolinensis), which outcompete red squirrels for food and habitat space. They damage trees by stripping bark and providing an entry route for pests and pathogens. This has severe economic consequences for our commercial woodlands and it is thought that these processes can prevent some woodlands from regenerating naturally
• Non-native deer, which cause damage to tree and shrub shoots, fray tree bark and alter the characteristics of woodland habitats. This affects the native species of woodlands, has a negative effect on timber quality and can also kill trees

Dealing with invasive species

Some invasive species are covered by the Wildlife and Countryside Act (1981). It is illegal to release most of them into the wild, even when they are taken from the wild.

If an invasive species is present on a site, you should attempt to identify whether removing it will help you meet your site management objectives. This calculation will be based on the severity and frequency of the species' impact, the species likely to move in to replace the invasive species and the trade-off between resources required to tackle the issue and the likelihood of a measure’s effectiveness.

Avoid inadvertently spreading invasive species

In the case of plants, it is important to avoid inadvertently spreading the species by attempting to destroy it. Japanese knotweed can regrow from very small root sections carried on boots or machinery. Rhododendron seeds are fine, plentiful and light. They are easily carried by the wind, boots, equipment and various means of transport. Himalayan balsam seeds are distributed far and wide by explosive pods.

Ethical issues

Removing animals from a site usually throws up ethical issues, especially in an urban setting, where the local community may be quite strongly involved with the site and its fauna.

A European Union Regulation on Invasive Alien Species came into force on 1 January 2015. This was a result of the EU's strategy to protect and improve European biodiversity – one of the strategy’s six targets relates to invasive alien species. You can read more about this by following the links below.

Contact us

If you would like to contact the Sustainable Forest Management Team in Natural Resources Wales you can send your enquiry to sfmt@cyfoethnaturiolcymru.gov.uk