By Alissa MacMillan
Q: We hear so much about the importance of native forests, but I was wondering about trees in cities and towns. Do they play an important role for the environment?
A: “Generally speaking, cities, by their very nature, eliminate nature,” says Dr. Gerald Mills, a physical geographer at University College Dublin. “They are almost exclusively designed for humans, for our desires and recreation.” The green spaces you do see in more urban areas are often playing fields with little tree cover, all with us in mind.
But in the last few decades, there has been a big shift to nature-based solutions, Mills explains, which means, “bringing nature in and letting nature do the job that otherwise hard engineering would do;” for example, to help protect towns from flooding rather than relying only on walls. There has also been an increasing move, especially after covid, to get more parks and greenspaces into urban settings and to get trees on the street.
“It’s a balancing act between wanting to do it and the cost involved,” he explains, Cork and Dublin not having much space available, as trees compete with cars and buses. Trees are “often clipped and managed,” as people don’t want them to interfere with things like overhead lines, but “there has been a shift, no doubt about it,” Mills adds.
He notes that lot of trees in the city are privately owned, on school grounds, religious grounds, hospitals, graveyards, and, crucially, in people’s gardens. “It’s astonishing the proportion of green spaces in the hands of private landowners,” he says. “Individually you might think it’s not much, but taken as a whole, you would be astonished by the amount of green space hiding behind roads. These play a critical role in maintaining the urban environment.”
The innumerable benefits of trees are by now well-known. They provide a habitat for birds, insects and animals, even if they stand alone. They offer an umbrella: if rainwater is caught by the canopy, it slows it down and provides storage. Mills explains of some trees, “If you pluck off the leaves, the surface they cover would be an acre.” Trees give shade in the summertime and are extremely effective, when it’s hot, at providing air conditioning. Only if the tree is under stress and doesn’t have access to water will it shut down.
“They can strip out pollutants in the atmosphere, they bind the soil,” and, when trees come together, you get the benefits of ecosystems services, birds able to move from one to another or to different parks if there’s a corridor. Trees help as an overall management strategy and they “make people a lot happier.”
ADVANCED PLANNING
All this being said, trees are not the climate cure-all.
“People expect too much of trees, that they will take care of all the carbon,” Mills notes. “But you can’t plant enough trees to take care of the carbon we’re consuming.” In fact, he adds, “the best way to preserve air quality is to stop polluting.”
All trees are probably a good thing, even in towns, but they aren’t all equal. Mills cites a well-worn phrase from the field: “Right tree, right location, right age.”
Young trees do very little; “trees start to do serious functions when they get mature,” he explains, so it’s a matter of advanced planning.
“You have to decide now what you want Cork to look like twenty years from now,” as a lot will die, especially if we plant the same ones. As one example, with the 100 Million Trees project from a few years ago, “all trees of the same age will all get old together and be eliminated together.” Instead, you need a variety of species, ages, and sizes, particular to the needs of each place.
REGIONAL TOWNS
“Strategic greening” looks to whether a town is at risk of “Fluvial flooding,” or water overflowing from the river, or “Pluvial flooding,” where, with intense rainfall, the piping system is not able to cope and water pools on the land. Clonmel, for example, occupies a flood plain and trees would be of great benefit, but it might already be too late, and they will need to build high walls.
“Fermoy won’t be sorted out by planting trees, it’s too big,” he says, noting that sometimes what you can do locally is very limited, it being more about a possible land reserve further up the river, for example, to store water and prevent it from overflowing.
Urban greening is of course a global concern, some cities taking more of a lead. “A lot of Nordic cities have a fair amount of greening,” says Mills. “London, given its size and extent, does a fairly good job; and the same is true of Paris, the most densely occupied city in Europe but dealing with the challenge and putting efforts into greening.” Mills noticed greening as ornamentation on a street in Cork recently, offering a source of happiness which gets us out of the house. Other strategies, like the trees in wheelbarrows outside Limerick train station, give a small amount of green but can be moved.
Even hedges provide shelter and shade. “Removing hedgerows sometimes makes a big difference to how people experience the environment,” Mills says, pointing to the example of Tallaght, where they got rid of hedgerows and ended up losing air protection in the town.
Because of the difficulty faced by city councils, either forgoing income or contending with ongoing maintenance, residents are often encouraged to improve their green covering when possible. Many argue there should be metrics showing the proportion of green or a calculation of tree canopy cover. In Europe, ideal cover is considered 25-30% of urban space, which can be difficult in occupied parts of the city but easier in suburban areas.
Mills suggests getting community members together for a kind of tree census of your neighbourhood, mapping out every tree, identifying where there are none, and measuring their width and dimensions. “Once you measure the breath of a tree, you can figure out the solid carbon and water in there and can gather the information and make the case for trees yourself,” he says.
“The whole point of being in a town or city is getting the benefit of mutual cooperation and the shared space should be pleasant for all.” The greener the better, for the weather, soil, happiness, and improving the habitat for all creatures.
