Do you have a favourite tree? In a year when we have all spent more time outdoors and rekindled our love of nature, that might be more likely than ever. Sadly, the threat to our trees is real and increasing, from climate change but also global trade practices, which, if unchecked, enable the fast-spreading of pest and disease. There are 27 notifiable suspects in the UK. Some will eventually kill a tree outright; others will weaken it to make way for another pest, pathogen or period of drought to finish it off.
But all is certainly not lost: we can help to protect our trees. First, we must know what to look out for: the more we all monitor the situation, the more we can curb transmission. So here are three trees that need our help right now and what to look out for...
How to spot it
Look out for the borer’s metallic-green adult form, up to 13.5mm long, and for horizontal fractures and D-shaped holes in bark. Chalara causes a blackening and wilting of leaves and shoots in summer, premature leaf fall and dark, elongated, diamond-shaped lesions on the bark (visible year-round).
How to help
Use TreeAlert or TreeCheck for possible sightings of emerald ash borer. Chalara is notifiable only in areas where it is new (see chalaramap.fera.defra.gov.uk). Sadly, these are few and far between. Keep an eye on progress at the Living Ash Project, which has planted 3,000 disease-tolerant saplings in Hampshire, using citizen scientists to help identify resilient strains.
How to save our trees
1. Never bring home any plant material from abroad. Even a healthy-looking plant could be carrying a pest or disease.
2. Learn the signs of tree ill-health and how to respond. This Government page has clear instructions and a link to the Forestry Commission’s notifiable pests and diseases with details on each. The Yorkshire Arboretum’s new Tree Health Centre opens in the spring.
2. Choose specimens carefully. Does it have a ‘plant passport’ that tells you where it was grown and how it has got here? Look out for the Plant Healthy green leaf symbol – the equivalent of the Red Tractor mark on British-grown food. If planting several new trees, plant diversely, mixing up species of trees, both native and exotic. Single-species woodlands create hotbeds for disease. “It’s a classic problem with an obvious solution,” explains Dr Grimshaw. “Trees of the same species need to socially distance.”
4. Be a conscientious citizen scientist. As well as alerting the authorities, you could contribute your findings to the tree-health monitoring programme Observatree.
5. Observe plant hygiene rules. Brush soil and all plant material from the soles of your boots and wheels of bicycles or buggies before leaving woodlands, parks or gardens, and wash them down at home before visiting another site.
What will happen if we lose these trees altogether?
The impact is not just on the look of the landscape. It is also financial – larch and pine plantations have suffered devastation from disease – and environmental, with habitat loss for invertebrates, lichens, mosses and birds. A butterfly, the white-letter hairstreak, depends on the elm for its home. No elm, no butterfly.
What's happening right now to help?
Professor Nicola Spence, chief plant health officer at Defra (Department for Environment, Food and Rural Affairs), is on the frontline battling the pests and pathogens that threaten our landscape. Her role is to command the national response through policy and partnership. As she says, it’s all about vigilance: “Prevent. Check, check, check. And invest in science and research.” Charities, landscape architects, horticulturalists and landowners all have a part to play – as does every one of us.
The Asian longhorn beetle, a threat to many broadleaved trees, has been eradicated after a six-year trapping and monitoring campaign. Strict biosecurity operates both for shipments of living trees and consignments of timber, while scientists are leading research programmes, mapping genomes and developing varieties of disease-resistant trees.
Spring 2021 will see the launch of a Tree Health Centre at The Yorkshire Arboretum, beside Castle Howard, to educate everyone, from homeowners with a few garden trees to highway-maintenance teams and railway workers. In the classroom, the laboratory and the arboretum, students will learn the hallmarks of a healthy tree, the symptoms of pest and disease and how to respond. “This is a critically needed public outreach programme,” says Dr John Grimshaw, director of The Yorkshire Arboretum. “Everyone has a stake in tree health. We need to promote knowledge and we need to change behaviour.”
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