Much of the commentary around achieving a target of 16.5% of woodland cover across the UK by 2050 focuses on new planting – but preserving existing stock is equally important.

Since 1971, no less than 24 new disease and pest outbreaks have occurred across the UK (Figure 7). Some have passed with little impact, while others, like Dutch elm disease and ash dieback, have inflicted severe damage on tree populations. The rate of new appearances of outbreaks seems to be increasing. Before the new millennium, a maximum of two new outbreaks were reported each decade. In contrast, during the 2000s there were seven and in the 2010s there were eleven.

The butterfly effect

Since the 1970s, the average global temperature on Earth has increased by 0.15 to 0.20°C per decade. The decade to 2023 saw warming of 0.26°C. The number seems miniscule; few would notice a 0.2°C increase in the temperature on any given day. However, an average change of less than 2°C plunged the Earth into the Little Ice Age for centuries. A small change delivers potentially greater consequences over time.

One consequence of the warming is the greater prevalence of pests and disease and their impacts:

• More pathogens and pests not previously seen in the UK are now able to survive here.

• Some pests, particularly insects, can reproduce more frequently in warmer weather. This results in longer periods of pest activity and a wider spread and greater population of these pests.

• More generations also increases the ability of pathogens to adapt and evolve to chemical treatments or resistant tree species, rendering mitigation measures less useful.

• Milder winters and wetter springs can see some species survive throughout the year and thrive in spring.

• Other climate impacts, such as storms and drought, leave trees more susceptible to pests and disease.

Provenance of pests

Climate change cannot be solely blamed for the propagation of tree pests and diseases. Equal blame can be attributed to the increase in demand for timber. Higher demand also leads to increased trade to provide sufficient supplies.

According to HMRC, the UK imported significant quantities of rough or simply-worked wood (at least 1,000 tonnes) from 36 nations in 2023. Some of the most destructive diseases listed in the timeline (Figure 7) are believed to have originated within imported rough timber. Dutch elm disease, which killed 30 million trees, is believed to have arrived in the UK in the late 1960s as a result of imported shipments of elm logs from Canada. Phytophthora ramorum likely arrived on infected garden plants from Europe. While phytosanitary standards are continuously improving, it seems likely that future problems could arrive as a result of trade.

Changing practices

Increased demand also brought changes in woodland management. Certain forestry practices, such as monoculture plantations, can create environments where pests and diseases spread more easily. However, practices such as selecting disease-resistant species can reduce the likelihood of spread – and when used together with other measures, such as regular monitoring and enhanced biosecurity measures, can help to mitigate the impact of pests and diseases.

Consider the eight-toothed spruce bark beetle, how it came to the UK is unknown and without mitigation, it has received the maximum possible score on Defra’s UK Relative Risk Rating. The Relative Risk Rating considers how likely an outbreak is, how much value is threatened and what the impact on that value is likely to be. With mitigation, the risk remains significant but is substantially decreased by 36% due to the reduced likelihood of establishment and economic impact. According to Defra’s Rapid Pest Risk Analysis, mitigation, in this case, consists of the “careful management of spruce forests in high-risk areas, through sanitation felling and the removal of susceptible material before any dispersal flights in spring.”

Endangered trees in the UK

Whitebeam species

36 species of whitebeam are listed by the International Union for the Conservation of Nature (IUCN) as anywhere from vulnerable to critically endangered. Of those, five are critically endangered, with still-decreasing populations.

Horse chestnut

Internationally, the horse chestnut is considered vulnerable by the IUCN, with populations decreasing. It has been facing particular pressures since bleeding canker and the leaf miner moth arrived in the UK.

Juniper

Juniper is one of the few native conifers in the UK but is nonetheless in decline. It may become extinct in lowland England without intervention. Its aromatic leaves and black berries are iconic and provide habitat for a number of bird species. It is vulnerable to both disease and overgrazing.

Black poplar

Now found mainly in Shropshire, Cheshire, Somerset and East Anglia – the black poplar used to be common along rivers and in the accompanying floodplains. However, land use change has seen those uses retreat. There are believed to be around 7,000 of this native tree across the UK with numbers declining.

Technology for trees

Globally, technological development is booming, with artificial intelligence (AI) now at our fingertips, drones available in supermarkets and fleets of interconnected sensors within our homes. How is this technology going to impact the forestry sector in the coming years?

Images

Forestry management is heavily reliant upon seeing the situation, but inspecting hundreds to thousands of trees on foot is inefficient. Imagery, whether taken from hundreds of miles above by satellites or up close by drones, reduces the level of compromise by allowing larger areas to be inspected. Satellite imagery data can be used for detailed forest inventories, including tree stocking and health analysis. Drones can quickly cover difficult-to-access areas, capturing detailed images and videos to detect disease, pest infestations, wind damage and other stress factors – allowing for timely interventions.

Sensors

Sensors can monitor greenhouse gas emissions, soil health and tree growth. While useful individually, connecting these sensors as part of a network can provide more comprehensive and higher-quality results. For instance, sensors can detect changes in soil moisture, temperature and nutrient levels, providing real-time data that helps in making informed decisions about forest management. Additionally, sensors can monitor tree health by detecting early signs of disease or pest infestations, allowing for timely intervention. The Internet of Things will facilitate this connectivity, while AI will enhance the analysis of the collected data.

AI

Images and sensors alone are not enough. Human assessment or basic digital analysis is required to interpret the data gathered. The advent of AI promises to enhance the quality and speed of this analysis, freeing up resources for other tasks and delivering improved outcomes. By analysing vast quantities of data from all these various sources, AI can deliver insights about the forest. For example, AI algorithms can identify tree species, assess biomass and predict forest growth patterns – enabling more precise and efficient forest management.

_{Read the articles within The Forestry Market – 2025 below.}