Globally, trees are primarily threatened by degradation or destruction of woodland for agriculture and timber production. In the UK these factors do not pose a significant threat to our native trees but this does not mean we are immune from problems. This week is National Tree Week in the UK so what better time to learn about the threatened trees of Britain…

In the UK there are around 15 threatened trees. The majority are endemic species of whitebeam (Sorbus spp.) but there is also the wild cotoneaster (Cotoneaster cambricus) endemic to North Wales, of which only 6 individuals are known. Other species such as the common juniper (Juniperus communis) and the woolly willow (Salix lanata) have only a few individuals remaining in the wild in Britain, but are fortunately more common in mainland Europe.

Timber Production During the World Wars

Although no longer a large threat to Britain’s trees, timber production had a significant impact on the British woodland landscape during the First and Second World Wars. Timber shortages meant that native woodlands were cleared and plantations of mainly exotic conifers such as Sitka spruce, Douglas fir and Western red cedar, which grew much faster than native species were grown.

UK native woodland trees, and other woodland plants and animals suffered severely under these shade-bearing conifers. Careful management and conversion back to native forests is underway and it is believed that Britain’s total area covered by forest has doubled since the First World War.

However, while UK forest cover may be increasing, Britain’s native trees face a greater threat from pests, diseases and climate change.

Pests and Diseases

Britain’s trees are under increasing threat from new pests and diseases that have, in most cases, entered from abroad. These non-native species, which in their natural range are kept in check by natural predators and environmental conditions, could have a potentially devastating impact on the British landscape.

Global trade, particularly of plants and trees for our parks and gardens, and in some cases climate change, are responsible for introducing these unwanted guests into the UK. Much loved species like the ‘conker tree’ (Aesculus hippocastanum) as well as Christmas tree species (Pinus sylvestris) have suffered considerable damage. Even the iconic English oaks (Quercus robur and Q. petraea) are being stripped of their leaves by the oak processionary moth.

Many will remember the devastation caused in the UK by the infamous Dutch elm disease in the 1970s; some 30 million trees were wiped out and it is thought that without proper control the same could happen with the recent introduction of Chalara dieback of Ash.

The International Plant Sentinel Network is jointly led by BGCI (a GTC partner) and DEFRA and works with botanic gardens and arboreta around the world to provide guidance on diagnosis, monitoring and surveying of plant pests and diseases.

Kew’s Millennium Seed Bank is establishing the country’s first national collection of tree seeds - the UK National Tree Seed project. This collection will ensure the country has a genetically diverse assortment of seeds for research into threats facing trees. The focus is on native trees, in particular those species that are at high risk, rare or important in the landscape for example, common juniper, yew and common ash. These research efforts are essential for successful control and management of pests and diseases.

Climate Change

The native tree species of the UK have adapted to the climatic conditions that have arisen here since the end of the last Ice Age. Over the next hundred years or so the UK climate is predicted to change, winters may be milder and wetter, and summers hotter and drier. Changes in tree species composition in our woodlands are likely, as well as shifts in the range of woodlands.

One of the most unique, important and interesting habitats in the UK are ancient woodlands. These woodlands have a high conservation value as they are home to more rare and threatened species than any other UK habitat.

Ancient woodlands are areas that are believed to have had continuous woodland cover since at least 1600AD. They consist of trees such as native species of Hazel, Alder, Oak, Lime, Beech and Elm. They are one of our richest habitats for wildlife; many species entirely depend on ancient woodland for their survival. For example the violet click beetle (Limoniscus violaceus) breeds in the dead hollow trunks of ancient trees, usually Beech or Ash, and is one of the rarest and most threatened beetles of the British Isles.

Ancient woodlands are a vital part of UK heritage but they continue to be under threat from destruction, isolation, overgrazing and more recently climate change.

National Tree Week 23rd November to 1st December 2013

National tree week is an annual celebration of UK trees and marks the start of the winter tree-planting season. Here is a list of some of the things you can do to celebrate national tree week:

• Learn about the UKs threatened trees and why we should save them. Each day this week we will be adding a new tree to the Threatened Trees page
• Learn more about Ash dieback: http://www.youtube.com/watch?v=HIll-_blL5c
• Get involved in tree planting days in your local area, such as with the Tree Council
• Visit an ancient woodland, botanic garden or arboretum near you to see examples of threatened trees and learn about the conservation work of these institutions
• Support the work of the Global Trees Campaign