Tallest trees in Ireland reach 61.3m

Since the early 1980s, it has been recognised silvicultural practice in Ireland to clearfell forests before they reach the age of maximum mean annual (volume) increment (MMAI). After MMAI, cumulative volume growth decreases, so the economic arguments favour felling at maximum yield.

Since the 1980s, it has been common practice to clearfell high-yielding crops such as Sitka spruce, Norway spruce and Douglas fir before they reach MMAI. As a result, crops that normally reach MMAI at between 50 and 60 years are reduced to between 30 and 40 years of age – and sooner in very high-yielding crops.

Forests and individual trees that have been retained well beyond economic rotations are showing remarkable performances in Ireland, as recorded by Aubrey Fennell. These champion trees, once confined to parklands and estates, planted in the 19th century, are now being overtaken by forest trees almost half their age.

While retaining commercial forest trees indefinitely would be impracticable, there may be a case to extend rotations. The current practice ensures that Irish commercial conifer forests will never reach their potential heights and yields, not to mention their majestic presence. However, the retention of crops is not just an aesthetic or economic issue as there are other reasons to extend rotations, including maximising the forest’s role in climate change mitigation.

Extending rotations as outlined by the UK Woodland Carbon Code (WCC) can maximise forest carbon sequestration.

“Over the long-term average, taking into account the whole cycle of a commercial rotation, the sequestration rate can be as high as 3t of carbon (C) or 11t of CO2 per ha per year,” maintains the UK Forestry Commission (FC).

“Over a number of forest rotations, this commercially managed stand can be assumed to maintain around 100t C/ha (or 370t CO2) on the site on average,” explains the FC. “

The FC claims that if rotations were extended to allow commercially managed forests to “grow old naturally”, the average long-term stock per hectare taking into account natural disturbance, is estimated to be around 170t C to 220t C (620t C02 to 800t CO2).

The WCC initiative only acknowledges carbon sequestered in the forest and precludes the embodied energy benefits throughout the wood lifecycle.

Wood construction – including multi-storey building – is now regarded as part of the climate change solution, as timber products lock approximately 1t of CO2 per 1m3 of wood.

In 2016, Coillte’s Gerard Murphy outlined a number of “no-regret” strategies, including developing “sustainable forest management with a clear climate change focus”.

No-regret climate adaptation strategies are precautionary practices that respond to negative climatic impacts before they intensify.

At the time, Murphy acknowledged that maximising carbon sequestration would require “a change in forest management including extending the age of clearfell to beyond current financial rotations”.

He and others acknowledge the risks in extending forest rotations, the most obvious in Ireland is wind-blow. It’s no coincidence that none of the champion trees are growing in exposed sites or in the west of Ireland, and indeed some champion trees have been victims of recent storms, such as the Sitka spruce in Baunreagh, Co Laois.

Likewise, large trees require different sawmill technology as most mills in Ireland are geared to saw logs less than 1m3. However, the time scale of shifting from reduced to extended rotation would be a long-term strategy and would only affect timber processing in decades to come.

On the right site, it would delay costly reforestation while still providing excellent revenue from thinning mature crops. Extending rotations would provide opportunities to shift to other silvicultural systems including continuous cover forestry (CCF), which would provide biodiversity and aesthetic benefits.

For years, a Sitka spruce in the Curraghmore Estate in Co Waterford battled it out with a Douglas fir in Powerscourt Estate in Co Wicklow for the title of the tallest tree in Ireland.

Planted in 1835, the Curraghmore Sitka has a head start on all other species. By 1891, it had reached 33.5m, according to The Trees of Great Britain and Ireland by Augustine Henry and Henry John Elwes, published in seven volumes between 1906 and 1913.

By 1974, it had reached 49m but has slowed down over the years and today, at 56m tall, has slipped to joint 12th in the ranking.

The Powersourt Douglas fir has also slipped in the ranking and at 60.1m is now fourth, but the gardens still have the tallest western red cedar (48.4m) in Europe and tallest cedar of Lebanon (41m) in Ireland.

However, the former parkland giants have now been overtaken by much younger, mainly forest trees. Little more than 10km separates the tallest – both 61.3m – a Sitka spruce in Glendalough and Douglas fir in Avondale. The Sitka spruce in Lugduff above the Upper Lake in Glendalough was part of a forest established in the mid-1920s, while the Douglas fir in Avondale formed part of the trial plots laid down between 1905 and 1913.

These represent only a tiny fraction of trees measured by Aubrey Fennell, author of Heritage Trees of Ireland. He has recorded over 10,000 champion trees for the Tree Register of Ireland.

Broadleaves

While broadleaves don’t feature in the height champions, there are some impressive champions – a 38.4m beech at Hilton Park, Co Monaghan, and a 36m oak in Tynan Abbey, Co Armagh, head the list.

All the trees in Table 1 are native to western North America, where in their natural habitat reach heights of over 100m. The tallest giant, or Sierra redwood, is 76m in the Sequoia National Park, 20m taller than its Avondale cousin, but it has a 3,000-year head start.