RECENTLY, the Birmingham Forest Institute, or BIFor, hosted a high-powered meeting of international experts at the University at Edgbaston to provide updates on biosecurity related to trees and brainstorm the future.

The lineup of 14 speakers was truly international, with researchers drawn from organisations in Finland, France, Germany, Spain, Sweden, the Netherlands and the UK. Other nations represented included Colombia, South Africa, Canada and Benin.

What is BIFor?

Readers may not be too familiar with the innovative new Birmingham Institute for Forestry Research, which is part of the university and focuses on two linked challenges: the impact of climate and environmental change on woodlands and the resilience of trees to pests and diseases.

BiFor came about through a philanthropic donation of £15 million five years ago. Although under the College of Life and Environmental Science, it is not a physical unit in the university as such, but a consortium of researchers and students across a range of departments – another example of how modern forestry covers a far wider brief today than in the past. 

Its showcase is the state-of-the-art Free-Air Carbon Dioxide Enrichment (FACE) experiment, set up in mature, unmanaged, temperate oak woodland, on private land in Staffordshire. With canopy-soaring towers packed with high-tech gadgets and machines to pump out extra carbon dioxide into the atmosphere, it is geared up to fathom out how forests respond to environmental changes. The 10-year project is now in its fifth year, involving the collaboration of 30 research groups. 

BIFoR-FACE is only the second such facility worldwide, and the only one in the northern hemisphere (get along when you get a chance – and meanwhile take a virtual tour on YouTube).

Why hold this symposium?

All plants great and small are constantly exposed to abiotic (environmental) and biotic (pest and pathogen) factors. With an average life expectancy of centuries, trees have a strong immune system that allows them to survive these threats in the normal circumstances that they and their ancestors evolved under.

However, in the last few years we have witnessed unprecedented outbreaks of tree diseases such as ash dieback that neither the trees nor those who care for them have been prepared for. These events have been fuelled by climate change (rising temperature and CO2 concentration) and globalisation (movement of people and goods). 

Change is not new, but the speed at which these phenomena are occurring is. This leaves us and our tree cover vulnerable to unexpected and perhaps irreversible landscape transformations.

Much of the effort to control disease outbreaks is directed at short-term operational responses to immediate threats. Yet there is also the need to focus on enhancing our fundamental understanding of plant–pathogen–environment interactions in the longer term. It is clear too that the successful implementation of effective strategies and solutions cannot be achieved by individual countries alone, but is dependent on a global effort.

This international symposium, free and open to everyone, aimed to showcase the very latest work in plant pathology and tree research. The impressive gathering of investigators from the UK and abroad, with a background in forest and plant research, provided the right conditions for a global exchange of knowledge, common thinking and scientific collaboration towards forest biosecurity.

Forestry Journal: Conference organisers Dr Estrella Luna-Diez and Dr Graeme Kettles (photo courtesy of Team Thomma).Conference organisers Dr Estrella Luna-Diez and Dr Graeme Kettles (photo courtesy of Team Thomma).

The programme

The three sessions for the very full day were: Aspects of Forest Research, Enabling Tools in Plant Pathology and Research in Tree Pathology.

The second dealt in depth with the technical side of how to identify genetic markers on tree chromosomes that may indicate resistance to pests and disease and whether those can be modified or turned on in some way to combat infection.

Three particular challenges to trees in the UK came under review.

Chalara Ash Dieback

Bleak though the Chalara panorama may be, there are glimmers of hope. An optimistic note came from Benoit Marcais from France in his talk on ‘The Landscape Epidemiology of Ash Dieback’. He highlighted how plant pathology tends to be too pessimistic, with foresters using the impact of Dutch elm disease as the standard. 

His team’s studies in France since ADB first raised its head there show the incidence of this disease is patchy and may have been overestimated a little. Ash in mixed stands and isolated trees are showing less mortality in periodic surveys there.

Traps proved that spores can be dispersed over large distances – and could certainly cross the Channel. And there may be at least one advantage of global warming in that heat waves – temperatures of 35 degrees and above – are lethal for the ADB spores.

His prediction was that ash (F. excelsior) will not disappear completely because of dieback as the problem diminishes with lower tree densities, and a rise in temperature hampers the pathogen too.  

Screening of ash in the UK by Richard Buggs and his Kew crew revealed there is considerable genetic variation geographically in the UK which implies a better chance of at least some individual trees having a natural resistance or tolerance to this fungus.

So all is not doom and gloom.

Forestry Journal: Dr Adriana Puentes from Sweden on plant defences (photo courtesy of Team Thomma).Dr Adriana Puentes from Sweden on plant defences (photo courtesy of Team Thomma).

Lessons from Sweden – the Evil Weevil

Dr Adriana Puentes is a Colombian, trained in Toronto and working in Sweden on the pine weevil Hylobius abietis – an insect well known to upland foresters in the UK when replanting conifers on clearfell sites. The weevil is a big problem in Sweden’s extensive forests and across northern Europe. And from next year, the use of insecticides to combat the pest will be banned in Sweden, so a novel solution is sought to boost seedling defences.

Their work revealed how it is possible to prime and trigger the seedlings’ own natural chemical defences by treating them before planting.  

By screening for genetic variation for resistance and then bulking up and growing on material for resistance in vitro, seedlings termed ‘emblings’ (produced by somatic embryogenesis) result to sow and grow. These suffer less insect damage because the amount of natural deterrent chemicals already in the seedlings has been boosted or primed by human intervention.

Other Conifers

Prof John Mackay occupies is Wood Professor of Forest Science at Oxford University. His work concentrates on commercial conifers, which have well-developed breeding programmes. He pointed out that trees boast thousands of genes in their makeup – roughly 67 times more than humans. Several conifer genomes have now been sequenced and around one per cent of genes infer resistance.

The Spruce budworm is a major forest pest in his native Canada. There, a small proportion of spruce are naturally resistant to the insect; entomologists confirmed this is accredited to high levels of certain chemicals in the tree. That is determined genetically, offering the possibility of selective breeding based on naturally occurring resistance. So we are beginning to grasp why some trees are resistant and others not.

Forestry Journal: Prof Sandra Denman from Forest Research speaks on acute oak decline (photo courtesy of Team Thomma).Prof Sandra Denman from Forest Research speaks on acute oak decline (photo courtesy of Team Thomma).

Acute Oak Decline

Last but not least to take the stage was Prof Sandra Denman of the UK’s Forest Research, based down at Alice Holt. Her presentation was ‘A Holistic Research Approach to Understanding and Managing Complex Decline Syndromes in Oak’.

Sandra explained how multidisciplinary methods were used in an interdisciplinary way to investigate complex secondary disease syndromes on a long-lived host – Quercus robur and petraea. A decline is not the same as a disease, though it may weaken the host, so it is not always a vicious spiral. Up to 40 per cent of affected oaks can go into “remission”, though only time will tell if they can ever recover completely. From the 1980s, more oak were reported in a state of decline and AOD is now recognised as a distinct condition within the Oak Decline Complex. But what was causing this?

For the past 10 years, a team of researchers from different organisations – and several nations – have been cooperating on studying aspects of this complex condition to unravel its mysteries.

The first questions were: ‘Is this condition caused by a pest or pathogen?’, ‘What is its distribution?’, ‘Is it spreading and if so why and how?’ and ‘Can it be controlled?’
The Agrilus or jewel beetle is a prime player in spreading the two or three species of bacteria that cause the lesions – and all three are new to science and sometimes work in combination, but not universally so. Agrilus does not attack healthy trees and is a ‘finisher off’ rather than a primary killer.

Harnessing the power of citizen science was vital in determining the distribution of Agrilus – and showing it does best in warm climates, at low elevation, with low rainfall, and in places with high nitrogen deposits on oak leaves (as these are more nutritious). Low sulphur deposits play a part too. Sulphur has an antimicrobial effect so if sulphur emissions drop in clean-air areas, the disease on leaves actually increases. 

Low levels of nitrogen and phosphorus (and sometimes potassium) in forest soils predispose oaks to infection, as do soil compaction and acidification. So soil conditions are key drivers towards a decline in tree health as well. 

Oak is long-lived, and long-term monitoring is needed to fathom out what is happening – and the project has only been going for a decade. Studies have identified volatile compounds and specific pheromones to attract and trap Agrilus, remembering it is a native species, so not to be eradicated. Sandra reminded the audience that trees are a long-term business and that just because an oak it is beginning to show signs of decline does not mean it will soon die and needs felling.

Ivory Tower Syndrome

What was heartening was to learn how the benefits of ‘crowd-sourcing’ or sharing findings and cooperation between institutions and nations was paramount – as was the urgency to share information there and then in the fight against tree pests and disease, rather than keeping it under wraps for months or even years before it sees the light of day in a peer-reviewed scientific publication – the barometer by which many scientists’ performance and pay are still judged. The ivory tower syndrome appears to be crumbling.

Where do we go from here?

There is certainly a lot of good work in progress, but my conclusion – and I suspect that of most of the audience – was that while great strides are being made into unravelling the inherent and unseen ways that trees fight pests and diseases, there is no ‘silver bullet’.

Trees have complex genetics, are long-lived, large and so not the easiest organisms to study – and some of the diseases act only on a longish timescale. Breeding for resistance is not so easy, as resistance is often governed by multiple genes (polygenomic). And there is a lot more going on both inside the trees themselves and in their environment than was realised on the pests and diseases scene. What goes on unseen below ground is also crucial. The role of the fungal network or rhizosphere is only now becoming apparent. 

There also remains a lot to learn about how environmental factors affect the susceptibility of trees to decline and disease. The technology for unravelling genetic codes has progressed but is still complex and the study of pathogenomics is still in its infancy. 

A great deal has yet to be unravelled.