Researchers at Teagasc and TCD are discovering innovative ways to rejuvenate our ancient trees, writes Dick Ahlstrom
Ireland has a small and diminishing collection of giants - not characters from a panto but veteran trees. Efforts are now under way, however, to give our veterans a new lease of life and in the process protect this valuable genetic resource.
Teagasc's Dr Gerry Douglas of the Kinsealy Research Centre heads the project that also involves Trinity College Dublin researchers led by botanist Dr Trevor Hodkinson.
"Our main object is to conserve the very few veteran trees we have in Ireland to give them another lease of life because we have so few of them," says Dr Douglas. "The second object is to find out why they are so special. They are unique because they have lived so long and they may have genes that confer longevity."
A veteran in this case is a tree that has a circumference greater than four metres when measured a metre or more above the ground. Unfortunately, our collection of veterans is small, says Dr Douglas.
"Surveys for the Tree Register of Ireland record about 150 oak, 60 ash and 60 sycamore in the veteran class. By contrast, a recent survey of one English county recorded over 1,000 veteran oak trees," he says.
Many of our veterans have important cultural connotations, he says. The great King Oak at Tullamore is more than nine metres in circumference and probably survived decades of wind because it has a flat top and branches spread at wide angles. The Brian Boru Oak in Tuamagraney, Co Clare, is almost eight metres in girth and is named after our one and only high king of all Ireland, he says.
"The veteran sycamore at Kilmore Cathedral, Co Cavan, is seven metres in circumference, is hollow, is very healthy and has an estimated planting date of 1631. It was recorded by and named after the local Bishop Bedell, who was the first scholar to translate the bible into Irish," says Dr Douglas.
These trees also have very tangible importance, he believes. "They are an extremely important resource from the biodiversity point of view." They support thousands of species that live in the roots, branches, bark and the hollow centres of these trees.
"Our veterans are also a rare genetic resource. They are a living link to past generations of trees, which migrated naturally here from the Costa del Sol after the last Ice Age. The oldest veteran oaks in Ireland are about 600 to 1,000 years old. It is sobering to think they may link back just eight or 10 generations to those original colonisers."
The researchers are interested in the unique characteristics that allowed these remarkable trees to survive. "All trees would not grow to such a great age," Dr Douglas says. Seed lines scattered by trees die out. "There is a tremendous attrition caused by competition on the forest floor."
Many trees that could become veterans are cut down in their prime for timber, so there is some luck associated with becoming a veteran. Lightening strikes and wind take out others. "For the ones that really live to be an old age, despite the environmental conditions, there is a genetic component to their longevity," Dr Douglas believes, and the Trinity College connection will hopefully reveal some of these trees' genetic secrets.
Hodkinson and colleagues will do genetic fingerprinting of trees near the veterans to see if any genes have been passed across from the ancient trees given that many of them are still sexually active.
"We are not specifically looking for genes that give longevity. We want to see if the veterans have contributed to any of the trees in the surrounding area."
Dr Douglas notes, however, that "Methuselah" genes conferring long life have been identified in other species including microscopic worms and fruit flies. It is not inconceivable that trees might also have genes that predispose to long life.
The Kinsealy research group is involved in the conservation of the veterans. "We can extend their lives for another generation by propagating them vegetatively," says Dr Douglas.
They are concentrating on oak, ash, sycamore and elm and have collected shoots from the old trees. These in turn have been grafted onto fresh seedling root stock that has been species matched.
The elm is an exception, and will be grafted onto elm root cuttings from the veteran, producing a true clone. The team hopes that survivors of the devastating Dutch elm disease may have inherent resistance to the scourge.
There is no option with the other three species, but to make use of grafting as their roots will not take. "It is the only way we can propagate them," says Dr Douglas.
This year's grafting efforts have delivered promising results, with viable plants produced from oak, ash and sycamore. Significantly, the shoots have grown by a metre, much more than they would have had they remained on the veteran tree, says Dr Douglas. It may be that the old shoots are learning to behave like young ones after association with young roots.
"The grafted plants will be returned to the original tree owners at the end of the summer," he says.
"They will then plant them out and so the life of each veteran tree can be guaranteed to continue in a rejuvenated form." Additional cuttings will also go to the John F Kennedy Arboretum in Wexford in order to create a collection of veteran trees.
Very old trees, including the veterans, provide a largely hidden service on behalf of biodiversity. Their roots, bark and often rotting interiors support a remarkable number of other species, some of which now face extinction due to the diminishing number of old trees in our landscape, Dr Douglas says.
They are known as home to fungi, lichens, mosses, a host of invertebrates, microbes and slime moulds, he says. "The more obvious inhabitants: bats, squirrels and birds may have taken up residence too."
Once the bark of a very old tree has been breeched it succumbs to wet rot, but this too is of benefit to many other species. Some are highly specialised and depend on veteran trees and old trees to reproduce.
"Sadly we know that many of the specialised beetles and fungi found in veteran trees are in danger of extinction," says Dr Douglas.
"There are 447 fungi listed as endangered in the British Red Book, and 400 of these are most readily found in veteran trees and woodland. Similarly for beetles, we know that at least 12 old woodland species have become extinct since the bronze age."