Opinion: ash, elm and chestnut trees may be lost, but trees and the planting of trees are a key element of a net zero carbon plan
Over the past one hundred years, two iconic tree species have been lost from European and North American landscapes and a third is about to be lost. Each loss is a set of tragedies: the loss of a species, the loss of habitat, less space for associated plants and animals and the loss of the ways of life associated with the trades and crafts that used these trees.
Throughout this past summer it has been hard to avoid the evidence of how many ash trees (Fraxinus excelsior) are dying throughout Ireland. The tell-tale leafless branches poke out through the dark green canopies, clear evidence that ash blight, caused by a fungus, Hymenoscyphus fraxineus, is at work.
Since the disease was first noted in Ireland in 2012, it has spread widely, and the general consensus is that there is little that can now be done to save ash in Ireland or across much of Europe. Ash is still an important part of hedgerows in Ireland, accouning for almost a third of the trees found there. In broadleaved woodlands, ash became a widely planted tree to support the hurly making industry in Ireland. Native Ash woodlands are home to a broad range of native plants and the loss of this species will be a severe blow to biodiversity in Ireland.
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From RTÉ Radio 1's Drivetime, Mike McCartney reports on the tree disease Ash Dieback
In 1904, HW Merkel of the Bronx Zoological Park in New York City noticed the park's chestnut trees were dying. Over the next 40 years, the American chestnut (Castanea dentata) population declined from between 3 and 4 billion trees to a handful of solitary survivors. A tree that defined the forests of much of the east of America and was valued for food, timber and wildlife succumbed to a fungal infection, Cryphonectria parasitica, possibly imported to the US on plant stock sourced in China or Japan.
Just over a decade after Merkel made his discovery of blight in the American chestnut, a fungal infection was noted in elm trees (ulmus species) in France. By 1939, half of the elm trees in Holland were dead. Dutch Elm Disease, caused by the fungus Ceratocystis ulmi, relied on the bark beetle Scolytus multistriatus rather than the wind to carry infected spores.
These beetles feed on the fresh bark of new shoots on the elm. The spores enter the tree and, after a few years, the fungal infection has killed the tree. There was a brief respite in the 1940s and 1950s as trees resistant to infection survived attack. Having crossed to America, the fungus developed an aggressive strain that has decimated the elms of Europe since the 1960s.
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From RTÉ Archives, Andrew Kelly reports for RTÉ News in 1985 on the felling of elm trees around St Stephen's Green in Dublin due to Dutch elm disease.
Few elms survive in Ireland today. In the countryside, elms were integral elements of hedgerows, while they had been planted in many towns as trees that were tolerant of the smoke and fumes of the urban environment. Mature elms surrounding St Stephen’s Green in Dublin were felled in 1985.
Each of these trees is now close to extinction. Research efforts to breed trees resistant to fungal infections is ongoing for ash, chestnut and elm, but these are long term projects, and we may never see these trees in their full glory across the forests of the northern hemisphere.
What has happened is perhaps an example of ecosystem collapse. This is a relatively new addition to the lexicon of environmental horror that the Earth of the 20th and 21st centuries has seen. As the name suggests, it is not just the loss of one species, but also the loss for other species of a habitat shaped by chestnut, elm or ash in a forest environment. Such losses cannot be undone. In the future we might expect more such losses. Plants and plant diseases traverse the globe, and it is only a matter of time before another tree species is subjected to a fungal infection.
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From RTÉ Radio 1's Morning Ireland, Fran McNulty reports that the State has fallen far behind in its tree planting targets
In a broader context, a recent report on the state of the world’s trees identifies agriculture, logging and grazing as the major threats to trees. Climate change, fire and disease are perhaps emerging issues. In all 0.2% of the world's tree species are extinct, almost 30% are threatened and 7% are possibly threatened. The growing threat of climate change causing drought, severe weather events and increased incidence of fire is ominous.
Trees and the planting of trees has become a key element of the net zero carbon plan. Plant trees to take carbon from the atmosphere and store it for hundreds of years, that is part of the plan. But if trees are vulnerable to the threats of a changing climate, as so many organisms are, how can we rely on them into the future, for centuries to come?
We need forests with a range of species that will not all succumb to disease and should draw on the native species of Ireland
Sitka spruce (Picea sitchensis) is the main tree of the Irish forest estate. Sitka spruce is native to the moist temperate forests along the northwest coast of America and Canada, where the old growth forests are complex ecosystems and home to many species of plant and animal. In Ireland, Sitka spruce or other conifer woodlands are neither old nor complex habitats of the homeland. The forests that we need to store carbon into the future will need to be mixed, so we have a range of species that will not all succumb to disease and should draw on the native species of Ireland so that habitats for more than just exotic trees can develop.
Ecologist John Cross published an outline map of the potential natural vegetation of Ireland some years ago. This was a view into a future landscape that was shaped by woodlands of montane birch forests, oak forests, forests of oak and ash with hazel. Such a tapestry is the one we should aspire to for the future, one without ash. It has the potential to increase biodiversity, store carbon, enrich soils, provide for recreation and tourism and hopefully prove resilient to the pressures of diseases and maybe even climate change.
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
