Tackling Tree Disease in the UK

2nd Dec 2012

It isn’t simply Ash Dieback that’s threatening the forests and woodlands of the UK. A plethora of pests and pathogens are on the horizon, with the numbers of diseases afflicting our trees having increased markedly over the past twenty years. A panel of experts, assembled by the Parliamentary Office of Science and Technology for an evening event attended by the BES Policy Team on Tuesday, provided a rather gloomy overview of the challenges facing Government, land managers and the public in trying to keep the UK’s borders secure against these invaders for as long as possible.

Dr Joan Webber, Principal Pathologist at Forest Research, showed a graph at the beginning of her presentation, illustrating the almost exponential rise in tree diseases over the past decade. A bigger impact from tree diseases has been seen in this country over this time period than over the whole of the last century. Pathways for introduction include timber, wood and wood packaging, although the industry has come a long way in terms of treating this material to prevent infectious organisms being transported. Over the past 20 years the predominant means of introduction has been through the movement of plants. The expansion of global trade has accelerated these introductions: Ash Dieback, caused by Chalara fraxinea, most likely originated in East Asia (Japan and Korea).

Infected plants are extremely hard to identify, because of the sheer numbers of plants entering the UK, their complexity, heterogeneity and differences in size. Spores and symptoms can be hard to spot as these may be cryptic. The UK relies on inspection by individuals, rather than technologies to identify infected plants, rendering this a huge task.

The challenges of identifying organisms that pose a danger to our plants and trees is made more acute by the fact that damaging organisms may behave very differently in the UK than in their normal habitat. When introduced to a novel environment, the organism may be subject to different pressures, acquiring new mutations and adaptations.

Martin Ward, Head of Plant Health and the UK’s Chief Plant Officer at FERA, provided an overview of the policy context in which threats to trees can be tackled by EU Member States. It was clear that this is a complex area, which can perhaps cause confusion for land managers and others trying to understand who to work with and what to do to tackle infection. The EU is currently reviewing legislation concerning plant biosecurity for the first time since the 1970’s so it must be hoped that this streamlines policy and processes somewhat.

Whilst the UK has become better at diagnosing diseases, progress on detection is still lagging behind, with little made in 20 years. Martin Ward suggested that the UK needs to become better at using citizen science, a recommendation of the 2011 Defra and Foresty Commission Tree Health and Plant Biosecurity Action Plan, and at using acoustic and other methods of detection when plants enter the country’s borders.

Dr Hilary Allison, Director of Policy at the Woodland Trust, provided an NGO perspective, focusing specifically on Ash Dieback. Seventy to 75 percent of ash trees could be lost in the UK to the disease. In Denmark, only five percent of ash remains free of symptoms, whilst in Poland 15-25 percent of trees seem to have been spared. Populations of ash could be repopulated through selection and breeding of the uninflected trees.

The largest loss of ash trees, from the perspective of the public, will be seen in hedgerows and in public parks. The complex make up of hedgerows means that here it is hard to re-establish ash trees once lost. From the perspective of organisms, many depend on ash trees for food and shelter, with veteran ash vital critical for beetles that feed on dead and decaying wood. Ash Dieback then will have long-lasting implications for our countryside from both a human and a wildlife perspective.

The Woodland Trust is responding to Ash Dieback with a large conference in 2013, to consider how this and other diseases will impact on conservation. The Trust has also called for long-term investment in UK nurseries. Believing that they were sourcing trees grown in the UK, the Woodland Trust inadvertently sourced trees with a UK provenance but that were shipped out as seedlings to be grown in the Netherlands. This may have introduced Ash Dieback to the UK countryside in some instances. Finally, in common with Martin Ward’s call for the same, the Woodland Trust will encourage the development of citizen science, with the public playing a crucial role in detection and early-warning systems.

The final speaker, Dr Steve Woodward from the University of Aberdeen, highlighted the scale of the trade in plants globally that has led to the huge increase in incidences of plant disease across Europe. Many invasive species enter Europe from North America and Asia, with the latter the current largest source because of its economic dominance. Once these organisms enter Europe there is a huge nursery trade between European countries. Tonnes of soil are transported with plants from China and elsewhere, and whatever is in the soil accompanies that plant on its onward journey. Dr Woodward criticised our desire for ‘instant landscapes’ and ‘instant plants’ preventing countries from growing their own plants to size, rather than importing fully grown trees from elsewhere.

Given the hundreds or perhaps thousands of know and unknown tree diseases that could threaten UK landscapes, it could be assumed that a large amount of research would be in train to understand and deal with these. Unfortunately, Dr Woodward said, the UK compares poorly to other EU countries in terms of the numbers of scientists researching this issue. Forest pathology research in universities in fact seems to comprise just Dr Woodward himself. Delays in understanding Ash Dieback, Dr Webber suggested, have been caused by scientists taking a little while to realise the significance of this pathogen, whilst the ‘radar of scientific research and science funding’ has had to swing across too, to this new area.

The announcement recently of a new Tree Health and Plant Biosecurity Initiative, funded by the Biotechnology and Biological Sciences Research Council (BBSRC) could go some way to address the limited research effort that seems to be have been expended in this important area. Several millions of pounds of funding will be available over the next few years, with an announcement of opportunity expected in April 2013. What seems clear is that to tackle the diseases listed by Dr Woodward, from Oak Wilts, to Spruce Budworm, Pitch Canker in Pine and the Emerald Ash Borer, and not least Ash Dieback, will required concerted and interdisciplinary research, together with excellent governance and leadership by policy-makers in the UK, Europe and internationally.

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