Manage threats to woodland: destructive animals, invasive species

How to deal with threats - like grey squirrels and rhododendron - to protect native species and habitats in woodlands.

Applies to England

This guide summarises the threats to woodlands from issues such as:

  • browsing by deer and wild boar
  • damage from grey squirrels
  • invasion by non-native species, including plants

Read guidance on how to manage woodlands to benefit biodiversity.

Under the Wildlife and Countryside Act (1981), it’s illegal to release most invasive species - including non-native deer and ‎grey squirrel - into the wild, even when the plant or animal was originally taken from the wild.

Deer and feral wild boar

All species of deer are increasing in number and expanding their range in England and Wales. Wild boar are also expanding their range in England and in the longer term may be expected to establish in areas of high woodland cover over larger areas of England. Although deer and feral wild boar have value - aesthetically, culturally, as a sporting quarry and for their meat - they can also have negative impacts.

Populations which become too great can lead to:

  • damage to trees, hedges and fences, to woodland flora and non-woodland habitats
  • increasing traffic accident numbers
  • poor health within localised populations
  • winter starvation

Advice on dealing with deer and feral wild boar

Forestry Commission Deer Officers based in Area Offices are able to offer advice on deer and feral wild boar, their impacts on woodlands and their management, including availability of grant funding. Comprehensive Best Practice Guidance provides further detailed information on deer and feral wild boar.

Read managing deer for woodland biodiversity (PDF, 171 KB, 2 pages) for further information on the impacts that deer have on plants and animals and the options you have in dealing with them.

Deer and woodland creation

The Nature for Climate (NFC) funded proposal to increase tree planting to 30,000 hectares per year by 2025 represents the largest woodland creation programme since the mid-twentieth century. Deer are one of the greatest threats to trees during their establishment phase. Guidance: Woodland creation and mitigating the impacts of deer has been produced to help those involved in woodland creation understand the risks and how to mitigate against them.

Grey squirrels

The grey squirrel was introduced to the UK from North America in 1876 and its population has grown rapidly since then with detriment to our native red squirrel. Grey squirrels damage our forests and woodlands by stripping bark from trees’ main trunks (at the base and up in the canopy) and branches. When they strip a complete ring of bark around the tree, it will kill the tree.

The Forestry Commission is committed to helping you manage the impacts of grey squirrels in your woodlands by:

  • providing support through Countryside Stewardship (see below) for you to control grey squirrels where they’re a threat to management plan objectives - including conservation of red squirrels
  • supporting the UK Squirrel Accord partnership (see below), including its work to develop fertility control for the grey squirrel
  • taking action on its land holding (public forest estate) - see the grey squirrels policy and action plan (PDF, 161 KB, 5 pages) for more information
  • updating guidance on controlling grey squirrel damage to woodlands

Advice on dealing with the grey squirrel

Find more information and advice from Squirrel Accord - the partnership of 32 leading woodland, timber industry and conservation organisations was created following policy development discussions and formally launched by HRH Prince Charles in 2014. They aim to bring a concerted and coordinated approach to securing the future of red squirrels and woodlands, and to control the introduced grey squirrel.

You can also find out more about the management of grey squirrels from Forest Research.

Other invasive species

In 2015, the EU Alien Invasive Species regulations came into force including a list of 49 ‘Invasive Alien Species’ of EU concern for which the UK must take action to eradicate if found here unless the population is already well established. See the full list of Invasive Alien species.

In the UK the Invasive Non-native Species Strategy has been developed to give a strategic framework within which the actions of government departments, their related bodies and key stakeholders can be better co-ordinated. This should help you meet the challenge posed by invasive non-native species.

Invasive plant species of particular concern in woodland

Invasive non-native plants that may cause problems in the UK include:

  • Japanese knotweed (Fallopia japonica)
  • Himalayan balsam (Impatiens glandulifera)
  • rhododendron (Rhododendron ponticum)
  • giant hogweed (Heracleum mantegazzianum)

The first 3 are a threat to native flora and habitats, as they are aggressive and form dense stands that exclude other plants. Giant hogweed is less aggressive to other plants, but is poisonous and can cause severe skin reactions.

Find out how to prevent the harmful spread of invasive plants. See detailed advice on preventing the spread of Japanese knotweed and managing and controlling rhodendron (PDF, 1.57 MB, 44 pages).

Invasive animal and insect species

Invasive non-native species include:

  • grey squirrels (Sciurus carolinensis) - they outcompete red squirrels and damage young trees - see above
  • American mink (Mustela vison) - they threaten birds and mammals inhabiting river systems (which may be present in your woodland)
  • Muntjac deer (Muntiacus reevesi) - becoming more abundant and widespread and cause damage to tree and shrub shoots - see above
  • Citrus longhorn beetle, Anoplophora chinensis

Advice on dealing with non-native species

The GB Non Natives Invasive Species (GB NNISS) secretariat offer online tools and information including species risk assessments, species fact sheets and species management advice.

How Countryside Stewardship can help protect woodlands

For grants, find out about the eligibility and requirements for the woodland improvement option of Countryside Stewardship, which offers incentives to control deer, grey squirrels and non-native species including the control of rhododendron.

Find out more about grants and funding to create and manage woodlands in the create woodland: overview guide.

Published 9 July 2018
Last updated 3 December 2020 + show all updates
  1. Addition of guidance about woodland creation and deer.

  2. The advice on dealing with feral wild boar has been updated.

  3. First published.