The list of tree diseases keeps growing.
I have always found a high degree of comfort working with woods and trees. The way they reflect the steady rhythm of the seasons, the anticipation of annual events such as the flowering of the bluebells. But most of all comfort comes with working with such magnificent, robust and (on the whole) adaptable and long lived organisms, and such self-sustaining ecosystems. I also get to see the slow and dignified decline in veteran and ancient trees which adds further to the character and interest of these trees as they become their own living ecosystem, slowly decaying back into the soil to nurture the next generation.
Over the last few years however that comfort has started to be replaced by concern, brought about by the increasing incidents and impact of new tree diseases in this country. While climate change is certainly causing increased stresses to our trees (through the impact of increasing periods of drought or late frosts, for example), it is the growing list of new tree diseases which are starting to have the more marked impact.
We have always had episodes of high impact tree diseases in the UK – Dutch Elm Disease is one probably most of us can remember. A quick look through the Forest Research website shows a whole host of tree diseases, largely new to the UK and now of growing consternation. Some of particular note are:
- Acute Oak Decline (AOD) – a disease spreading through the English midlands on our native oaks which appears to be caused by a bacteria new to science
- Chronic Oak decline (COD) – also affecting our native oaks where a number of fungal and insect pest appear to have a role, although also most likely linked to trees already under stress from environmental conditions
- Horse Chestnut leaf miner – which turns the leaves for these important amenity trees brown early in the season, caused by a moth which has naturally spread into the UK in response to our warming climate
- Oak processionary moth – imported into London from Europe on trees planted at a local development site, which not only impacts on oak trees but through the hairs on the caterpillar has a potential human health impact
- Phytophthora ramorum – a fungal like pathogen that was brought into the country on imported rhododendron but has now jumped host and is affected Larch trees across much of South West England leading to extensive and large scale felling, including on Planted Ancient Woodland Sites (PAWS).
Of course wood boring and leaf eating insects and wood rotting fungi are vitally important parts of any woodland ecosystem. But what is perhaps more worrying is that these diseases in many cases are being “brought” to the UK by human activities, through the importation of infected plants for gardens and landscaping. Many of these diseases are no respecter of age, and all have an impact at a wood level; in the case of AOD and Phytophthora ramorum can rapidly lead to the decline and death of infected trees. And because of the sheer range and number of new diseases, the range of tree species affected and their actual and potential impacts, things do feel different at the moment.
So what is being done?
The Woodland Trust has been actively involved in and supports the government’s recently released Interim Tree Health and Biosecurity Strategy. We have also completed our own Tree Diseases (Biosecurity) position statement which explores the issues and outlines our approach. Plus we have helped along with others to fund some of the ongoing research in this area, and Woodland Heritage (a charity concerned with maintaining the traditional management of our woods and promoting the value of our native timbers) is seeking donations at the moment to support work to further develop understanding of Acute Oak Decline in the UK.
We have already had a number of our own woods affected by AOD, COD and Phytophthora ramorum. To me this feels like just the start. From now on we can’t feel quite so confident that the UK’s woods and trees are as robust as we would like to believe.
Andy Sharkey, head of woodland management