Image shows an ash tree in a field

Table of contents

On 9 June 2022, the House of Lords is scheduled to debate the following question for short debate:

Lord Harries of Pentregarth (Crossbench) to ask Her Majesty’s Government what assessment they have made of the health of trees in England; and what progress they have made towards developing a variety of ash that is resistant to ash dieback

1. Trees in the UK

1.1 How much of the UK is woodland and trees?

The government’s forestry statistics state that, as at 31 March 2021, there were an estimated 3.2mn hectares of woodland in the UK, or about 13% of the land area of the UK. These figures are slight increases from 2010, when there were 3.0mn hectares (also 13% of the total land area). However, they are significant increases from early in the 20th century, when around 5% of the UK land area was woodland.

In 2021, woodland represented 10% of land area in England, 15% in Wales, 19% in Scotland and 9% in Northern Ireland.

In addition, the Forestry Commission estimated there were 742,000 hectares of trees outside woodland in Great Britain in 2016. It said that 74% of these trees were in rural areas and 26% in urban areas. 51% of the UK woodland area in 2021 was planted with conifers, of which the most common species were the Sitka spruce and the Scots pine. 49% of the woodland area was broadleaved species, of which the three most common types were oak, birch and beech.

Across the UK as a whole, around 73% of woodland was in private ownership and 27% was owned by government bodies (such as the Forestry Commission in England). The proportion in government hands varied from 16% in England to 52% in Northern Ireland.

1.2 What is the estimated economic value of trees?

In 2018, the government made a “partial” estimate of the economic value of trees of £4.9bn per year. This included an element of market value, for example forestry and primary wood processing. It also included estimates of non-market value, such as the benefits for biodiversity, recreation, absorbing air pollution and physical and mental wellbeing.

The government also made an “initial” estimate of the asset value of UK trees of £175bn. It said this was produced by considering the annual economic value over 100 years and adjusting for factors such as population and income growth, while discounting future benefits back to current values.

2. Threats to UK trees

2.1 What threats do UK trees face?

UK trees are threatened by a wide range of pests and diseases, and these have increased in recent years.

Overall, the UK plant health risk register lists 1,295 pests. The government’s tree health resilience strategy said that approximately 30% of these are capable of attacking trees. The strategy said that risks to trees have risen for reasons such as:

  • globalisation, which has led to an increasing number and diversity of plant imports—one of the primary ways that new pests and diseases are introduced
  • evolution or cross-breeding of pests and pathogens, resulting in more virulent threats
  • neglect of woodland due to an increase in use of wood substitutes; for example, steel, plastic and concrete
  • climate change, for example because milder winters can provide more conducive environments for pests and diseases and because changes in seasonal variations could put trees under greater stress

The Woodland Trust provided more detail on 24 of the key pests and diseases currently attacking UK trees, including ash dieback, the bronze birch borer, plane wilt and the oak processionary moth.

A report by the Woodland Trust in April 2021 found that only 7% of the UK’s native woodlands were in “good ecological condition”. It found issues including low levels of deadwood, low numbers of “ancient” trees and insufficient diversity in ages and species of trees. The trust suggested that the reasons woodlands were in poor condition varied across the UK. For example, it said that England was characterised by “inappropriate management”, Scotland by damage from animals browsing and grazing, and Northern Ireland by “alien and problematic species”. The trust also argued that the rate of increase of tree cover was “nowhere near enough” and that only around 45% of new plantings were of native trees.

2.2 What is UK government policy to combat the threats?

The government’s 2018 tree health resilience strategy set out policies to combat the increased threats to trees. To counter the threat from imported plants, the government described inspections of plant and wood imports by the Plant Health Service at ports and airports. The government said that over the five years prior to 2018 the UK had made around 900 interceptions of harmful organisms. The Plant Health Service also produced factsheets, guidance and alerts for press articles, plant shows and social media.

Other measures included:

The strategy also set out an aim to increase tree cover in England to 12% by 2060 by planting 180,000 hectares of trees, including a new northern forest.

In May 2021, the government published an England trees action plan. It said the government intended to treble the rate of tree planting by the end of this parliament. The plan also announced that the government would fund a new Centre for Forest Protection to enhance the resilience of trees through “evidence, interdisciplinary research and expert advice”. The centre agreed its mission, vision, desired impact and desired outcomes in November 2021. Other measures in the action plan included setting out a woodland resilience implementation plan to increase the resilience of trees to climate change, pests and diseases. The plan provides a systematic method for assessing threats, deciding on responses and learning from the outcomes.

In September 2021, the government launched a consultation on an updated plant biosecurity strategy for Great Britain. Biosecurity refers to precautions that aim to prevent the introduction and spread of harmful organisms. The consultation sought opinions on a variety of measures. These included changes made since Brexit, such as an amended ‘quarantine pest’ list to focus on pests which pose the greatest risk in Britain. The consultation defines quarantine pests as those for which the UK has a comprehensive risk assessment and permanent import requirements to protect the country from them. It also described how the EU system of ‘protected zones’ had been replaced by ‘pest-free areas’, which the government said would allow it to manage the risk of quarantine pests that occur in parts of Great Britain.

The consultation noted that controls on plants imported from the EU were phased in between 1 January 2021 and March 2022. It stated that the UK remained a member of international biosecurity organisations such as Euphresco and the International Plant Sentinel Network. The consultation also included a specific section on ‘high-risk’ trees. It set out controls such as a prohibition on the import of specific tree and shrub types.

The government published a summary of responses to the consultation on 5 April 2022. It said responses emphasised the need for government to provide “clear, accessible, and succinct information”, including updates and alerts when new plant pests are identified as high risk. The summary highlighted the need for greater public awareness of the importance of plant health. Responses also called for greater “strategic long-term research” into plant health, rather than “reactive approaches”. In relation to high-risk trees, the government said respondents favoured prohibiting the import of certain plants, tightening restrictions on imports of larger trees and increasing the border inspection regime.

The government stated the next step would be the development of a new, five-year plant biosecurity strategy for Great Britain. It said this would be published later in 2022.

The Woodland Trust has also described its range of actions to improve the health of the whole UK tree stock, including:

  • closely monitoring the health of all trees and woods
  • allowing diseased trees to decline
  • increasing the genetic diversity of existing woods and planting a mix of species in new woods to improve their resilience to future diseases and to climate change
  • only planting trees that are sourced from the UK and Ireland—although the trust stated that UK and Irish tree nurseries cannot currently supply enough native trees to meet demand
  • participating in Observatree, a project that trains volunteers to spot pests and diseases, allowing tree authorities to manage outbreaks at an early stage

3. Ashes and ash dieback

The Woodland Trust described ash as “one of our most beloved trees”. The trust said that ash is one of the UK’s native tree types—that is, trees that grew in the UK before it was separated from mainland Europe. Non-native trees are those brought to the UK by humans.

3.1 What is ash dieback and what impact will it have?

The Tree Council has said that ash dieback is a “highly destructive” disease that affects ash trees.

The Woodland Trust states that ash dieback is a fungus that originated in Asia and was introduced to Europe about 30 years ago. The trust describes how the fungus produces spores that can blow “tens of miles” and land on leaves. The fungus then grows inside the tree, finally killing it.

The trust said the disease would eventually kill 80% of UK ash trees and “change the landscape forever”. It reported predicted costs arising from ash dieback of £15bn; for example, in the expense of clearing up dead and dying trees and the loss of “environmental services”, such as air purification, that ash trees provide. The trust reported that so far the disease has had the most impact in the south-east of England, although there was evidence of it throughout the UK. However, the trust argued that the UK is still at the beginning of the ash dieback “epidemic”, so the full impact will only emerge in time.

3.2 Combatting ash dieback

In June 2019, the government set out a strategy for conserving UK ash trees and mitigating ash pests and diseases. It stated that the government had invested £6mn in research into ash pests and diseases since 2012. The strategy argued that “good progress has been made in screening for tolerant trees and conserving the genetic diversity of our native ash trees”. The strategy set out key future policy initiatives, such as a new nationwide map of ash trees using remote sensing technologies.

The government also noted possible threats from the emerald ash borer, a small beetle that lays its eggs in ash bark. The government stated this pest was not present in the UK but has “devastated” ash trees across North America and is “moving west from Russia towards Europe”. The government said it was developing an “early warning system” to detect the pest if and when it arrives in the UK.

A range of actions to combat ash dieback rely on encouraging trees that appear to have a genetic tolerance to ash dieback. The Tree Council reported that several studies had found that a “low percentage”—perhaps 1% to 5%— of ash trees may have such a tolerance. The Woodland Trust said this meant the UK ash population could eventually recover, perhaps over 50 years. However, the trust said tolerance was “complicated”, with relevant factors including “genetic traits, the health of the tree and the number of ash dieback spores in the atmosphere”.

The government agency Forest Research, which describes itself as Britain’s principal organisation for forestry and tree-related research, said it was working to identify the genetic factors which enable some ash trees to tolerate or resist infection and was using these to breed new generations of tolerant ash trees. Forest Research was part of a consortium of organisations awarded a £2.4mn grant from the government for research into ash resistance. One area of research was to examine the genetic characteristics of more resistant and less resistant trees.

Another element of the consortium’s work involved planting 155,000 ash trees in 2013 and then taking grafts from the 575 which remained symptom-free five years later. It said these grafts, along with others from apparently healthy ash trees in existing woodlands, were being grown to form a source of seeds for future planting and an archive for researchers. Forest Research said that “all being well” this “seed orchard” should begin producing resistant ash tree seeds from the mid- to late-2030s.

As a fallback position, if it does not prove possible to breed tolerant trees from native UK ashes, Forest Research said it was also exploring whether it is possible to cross UK trees with other types of ash from abroad that have higher tolerance.

4. Read more

Cover image by WikimediaImages from Pixabay.