National Tree Week, currently in full swing, is organised each year by the Tree Council of Ireland. Its annual highlight is the Augustine Henry Memorial Lecture, named after the man allegedly responsible for the present-day composition of many of our Irish forests.
It was he, apparently, who first recognised that many trees native to the western side of North America, such as the Sitka spruce and Douglas fir, were climatically more suited to Irish conditions than many more familiar European species such as larch and Norway spruce.
But there is a mystery about our Irish forests. Forestry research has repeatedly shown that Ireland is one of the most favourable locations in Europe for growing trees, yet it is not only the least wooded country in Europe, but also has the lowest forest biodiversity. It was not always so; the three main reasons for the decline are climate change, geographical isolation and human exploitation.
Climate change brought on the last Ice Age. Few, if any, trees survived the southward movement of the polar ice sheet, but as the ice retreated, birches and willows gradually regained a foothold, to be followed later by alder, pine, and the oak and elm, providing a dense cover of forest. The range was restricted compared to the rest of Europe, however, because 10 or 12,000 years ago an inundation, originating from the melting ice, separated the land mass that was to become Ireland from what we now refer to as the Continent. Trees such as beech, lime and horse chestnut, though well suited to the Irish climate, did not reach us until they were introduced from abroad in the 17th and 18th centuries.
But little, if any, of the primeval forests now remains. A systematic devastation of Irish woodlands began following the defeat of the combined Irish and Spanish forces at Kinsale in 1601.
The devastation took place partly for economic reasons, since timber had become a valuable commodity, and partly as a military strategy, because the dense forests were ideal rallying-grounds and strongholds for the native Irish, and therefore were an inconvenience for our unwelcome visitors from across the channel. By the early 18th century, Ireland had become a treeless wilderness and a net importer of timber.
Dr Fraser Mitchell of the botany department of Trinity College is an expert on these matters. It is he who will deliver this year's Augustine Henry Memorial Lecture tomorrow evening in the Minerva Suite of the Royal Dublin Society at Ballsbridge. His title is "The Development of our Tree Cover over the Millennia". The talk will begin at 8 p.m., admission is free, and all are welcome.