Ireland’s trees in leaf earlier and longer suggest change in seasonal patterns

TREES in some of Ireland’s best-loved gardens appear to be wakening earlier as spring budding patterns change.

Volunteers gathered 7,500 observations from specimen trees from 1966-2020 and gave them to the Central Statistics Office (CSO) to analyse.

The results show marked differences in the length of time between the first day of leaf unfolding in spring to the first day of leaf fall in autumn, with the trend towards longer gaps over the last 15-20 years.

In particular, more of the earliest dates for spring unfolding have been clustered in the past decade and a half.

The observations record the main events in a tree’s season from the beginning of leaf unfolding to flowering, first ripe fruits, appearance of autumn colouring and leaf fall.

“Because many such phenomena are sensitive to variations in our climate, these records are a useful proxy for temperature in the study of climate change,” Paul McElvaney of the CSO’s environment and climate division explained.

While there were indications that the beginning of leaf unfolding in trees was happening earlier, he cautioned that more data was needed to confirm the trend.

The observations come from the National Botanic Gardens in Dublin, John F Kennedy Arboretum and Johnstown Castle in Wexford, Glenveagh National Park in Donegal, Enniscoe House in Mayo and Valentia Observatory in Kerry.

Key to this study were specimens of beech, larch, lime, wild cherry, birch and alpine currant whose every change was closely monitored throughout the years with some remarkable findings.

The number of days between leaf unfolding and leaf fall for the lime in Johnstown Castle almost doubled from lowest to highest with the earliest unfolding taking place on March 11 in 2019 and the latest on May 12 in 1979.

Similarly, the birch at Valentia had just 168 days in leaf in 1979 compared to 236 days in 2014. Leaf fall didn’t happen until November 26 that year.

Earliest leaves on the larch at Glenveagh appeared in 2009 and 2012 and the latest leaf fall was in 2016, while the while cherry at Enniscoe had its earliest leaves in 2015 and 2019.

The alpine currant in Dublin had a more varied record although it had more long periods in leaf in the lst ten years.

The beech in Wexford showed the least change over the period.