Dublin’s Trees: Summer’s Here, but Where’s the Shade?

Ireland is known for being green, but this isn’t always the case in Dublin. The city centre doesn’t quite fit with the Emerald Isle image.

There are a few parks and leafy corridors along the canals, where people sit and play guitars and read books and drink cans on hot summer days like Tuesday. But much of the city is glass, brick and cement.

In fact, a 2012 survey by a UCD researcher of the trees in Dublin counted just over 10,000 of them, which amounts to 734 trees per square kilometre, or approximately one tree for every 50 households in the area.

These include both street trees, which are nearly all immigrants, and park trees, many of whom are Irish. As a group, the city’s trees lack diversity, which leaves them susceptible to diseases and pests, and they aren’t numerous enough to drink up all the city’s carbon dioxide. But improvements might be coming.

The tree survey spanned a significant area between the Royal and Grand canals, stretching from Dublin Port to the edge of the Phoenix Park. Dr Tine Ningal, the UCD researcher who did this inventory, hopes his research will be used to inform the council’s planning and policy regarding trees.

Originally, he wanted to research the city’s air quality, but when the council had no data on the numbers of trees to calculate this, he instead turned to counting the trees himself. (Now Dublin City Council says there are 60,000 roadside trees in the city, and it’s unclear why there’s a gap between its number and Ningal’s.)

Ningal counted 41 different species of street trees, four of which were dominant; lime (same name, but not the ones you can make mojitos with), London plane, maple and hornbeam make up 84 percent of the total population. He puts their popularity down to their ability to survive in the urban environment.

None of these four types of trees is native to Ireland. In fact, none of the trees growing on our city streets are native. If you’re looking for Irish species, you have to go to places like the Phoenix Park, says Joe McConville, vice president of the Tree Council of Ireland and an arboriculturalist with more than 30 years experience.

Trees à la Mode

Different types of trees have come in and out of style in Dublin over the centuries, says McConville. As part of the British Empire, Ireland usually followed its forestation fashions.

In the eighteenth century, lime and linden trees were planted throughout the city by the authorities “which was traditional in those days”, he says. At that time, they were imported from Holland, because that’s where Irish plant brokers sourced all their materials.

By the nineteenth century, London planes became very fashionable. They were planted along the quays, in Trinity College, on Griffith Avenue and four were planted in Leinster House to commemorate Queen Victoria’s visit to Dublin in 1900.

From the 1940s onwards, not much tree planting took place, says McConville. “Then in the ’60s and ’70s, a lot was done in Dublin city’s parks and the planting tended to feature quite a mixed bag,” he says.

The pretty cherry trees around the city were planted at this time, but years later they started to cause problems by growing too big and lifting footpaths.

It wasn’t until the ’70s and ’80s that Irish nurseries got into the swing of things, says McConville. In the 1980s, maple trees started to become popular, and hornbeams also became prominent as local authorities used them to replace dying elm trees.

These days, Dublin City Council plants both native and non-native trees; ornamental types are used as street trees, while native trees are planted in woodlands because they are too big for the roadside.

Dublin City Council has created tree trails through a number of parks, to introduce people to Ireland’s native trees. You can print out the trail guide and visit Bushy Park or Herbert Park, among others, to learn about the 15 indigenous varieties, from holly and hazel to apple and oak.

So what trees should we be planting in our gardens at the moment? McConville ponders this question. “Pleached limes,” he says, like the ones along O’Connell Street. They are straight, upright and can have their branches intertwined to create a hedging effect.

Ornamental pear trees and other upright varieties generally are popular at the moment, McConville says. “Because of their narrow crown, they won’t get out of control,” he explains.

Air Quality

Once Ningal finished his inventory, he had a look at the effect Dublin’s trees have on our air quality. It’s a very small effect.

They sequester a measly 0.17 percent of the carbon dioxide the city’s traffic produces each year. “By international standards, Dublin’s trees carbon sequestration is insufficient,” Ningal says. “We need to plant more trees in all the green spaces.”

It’s not possible, though, to plant enough trees to take in all the carbon in the city’s air. “You’d be living in a forest,” comments McConville.

Still, Dublin’s air quality is better than New York’s and Tokyo’s, because the strong sea breeze and low buildings allow the carbon dioxide to be dispersed.

Of the different varieties of trees in Dublin, it seems that London planes take in the most carbon dioxide. According to Ningal, this is because many are more than 50 years old, and have big leaves and trunks.

But this doesn’t mean we should plant lots of London planes.

Safety in Diversity

On the contrary, both McConville and Ningal said a wider variety of tree types should be planted in the city. Currently, most streets feature just one tree variety, while a few have two or three.

“One problem within cities, particularly Dublin, is that when a tree is successful, we plant lots of them,” says McConville, “like London planes, but London planes are susceptible to two diseases which are currently spreading through France and have reached London.”

The fungus in question might not be suited to Irish weather, but McConville is still concerned at the prospect of diseases reaching our shores. Many horse chestnut trees were cut down a few years ago after an outbreak of bleeding canker in the Phoenix Park.

McConville is also concerned about pests, and specifically the Asian longhorn beetle, which recently reached the UK on untreated wood, and the emerald boring beetle, which could arrive from the US with wind turbines.

These beetles eat trees from the inside and the only way to control them is to cut down the affected trees. McConville believes they will eventually arrive in Ireland.

“We don’t have border control like Australia. The freedom of goods and services within Europe also makes this difficult . . . There is protocol, but nothing to stop someone not doing it,” he comments. “We’re relying on goodwill and honesty.”

Preserving and Planting

Dublin City Council has a good record for tree preservation. Even on private land, a felling notice needs to be issued before a tree can be uprooted or cut down. “Trees are generally prioritised when there’s development,” says McConville.

Some people will go so far as to build a house around a tree rather than cutting down the tree, says Ningal. They’ll excavate its roots like archaeologists and then build structures around them to keep them from interacting with the building, but allow them to get the water they need.

In addition to preserving the trees that are already here, Dublin City Council plants at least 5,000 trees a year, it says. That number might have to rise in years to come.

Ningal is part of an urban tree project that will present recommendations to the European Parliament in 2017. He hopes that a standard for urban trees across the continent will be introduced by 2020.

“I can see that one of the European directives will be to force local authorities to plant a certain number of trees in the city,” says Ningal.