Many trees that fell during Storm Ali were vulnerable because of a combination of prolonged dry conditions and soil contraction, a garden expert with the National Botanic Gardens said.
The number of trees lost in the storm has yet to be confirmed but Séamus O'Brien, head gardener of Kilmacurragh Botanic Gardens in Co Wicklow, said the storm provided further proof that climate change was generating different wind patterns that were detrimentally affecting Irish tree populations.
Unusually, the National Botanic Gardens in Dublin had a horrific time but Kilmacurragh got off lightly with the loss of just one birch tree, he said.
Trees, especially larger ones, were most vulnerable when there were “soggy wet” soil conditions, but when the opposite applied – ie dry conditions and soil contraction – they were vulnerable too and “more prone to rocking”, he said.
The effects of climate change, such as a changing of seasons, detrimentally affected trees, he added. In the case of Ireland it had also caused a change in prevailing winds, especially when storms arise.
Instead of coming from a southwesterly direction, as happened historically, they were now coming more from the east, as happened with Storm Ali and this caused more extensive tree loss. “This is part of the scenario of climate change,” he added.
While Ireland has lost many trees during storms over the past 18 months, about 1 per cent of all the trees in Ireland's forests fell during storms in the spring of 2014. The storms felled between 5,000 and 7,000 hectares of forest, mainly in Munster, a Government task force established.
The combination of saturated soils and gale-force winds, as well as the trees’ often exceptional size, proved to be a deadly combination.
Many of the tallest victims were non-native species, whose exceptional heights sometimes far exceeded those normally reached in their native habitat. They were taller as a result of the rich soil and mild climate in Ireland.