Trees in our cities, towns and villages

More and more people live in cities. There is a constant shift in habitation from the countryside to cities and the world now has more urban dwellers than it does rural ones – compared to 3% in 1800 and 14% in 1900. We crossed the 50% mark in 2008.

With the growth of urban culture, urban trees are more important now than they ever have ever been.  Trees in cities and suburbs will play an ever-increasing part in our lives.  It’s not just the big cities either: many of us live in country towns or villages where the view outside the windows and front door is the most important view in the world – or certainly the one we see the most often and over the longest period.

Plane trees (Platanus x acerifolia) in Dublin: Rathgar and Fitzwilliam Square.

The environment for a tree in a city is very different from a more natural rural setting. Water can be hard to access as it is whisked into drains by gutters and hard surfaces. Pollution can build up on leaves and bark. Greater extremes of temperature are likely as heat is stored and reflected off walls and roads. Soil is frequently contaminated with pollutants, chemicals or building materials. Wind can be intense as it is tunneled along streets. And there’s no end of potential for physical damage, either intentional – such as vandalism – or unintentional: bumps from cars, compaction around the roots and so on. In such an environment a tree can outgrow its available space, so it either needs to be able to take pruning or stop growing when it reaches a prescribed size.

Birch trees (Betula) around Dublin City centre: Dublin 8, Trinity College, Dublin 8 and Docklands.

Given all these constraints, some trees make better candidates for urban or suburban planting than others. Birches and Mountain ash species are good for confined spaces and they don’t undermine foundations or interfere with drains. Plane trees and Lime trees (known as Lindens in some parts of the world) are big trees which can take heavy pruning or pollarding. These trees are planted on the great streets of capital cities – from Berlin to Paris to Dublin – but also in country towns and villages. Hornbeams are adaptable to poor soil conditions, including compaction and bad drainage, and are one of the most commonly planted street trees along roads where they have to cope with heavy pollution, poor soil and bad drainage.  Other trees such as Robinia manage to grow tall but with an airiness that never casts too dense a shade.

Flowering trees on the street: Left to to right: Magnolia, Amelanchier and Laburnum

Trees in an urban environment don’t just have the difficult task of growing and flourishing. They have the difficult task of representing the natural world in a very unnatural situation. The cleverly planned Georgian squares of Dublin city centre were conceived as urban counterparts to many of the residents’ country estates: open space in the centre dominated by grass (like fields) with a densely wooded ‘ride’ around the outside. In a city that was – and is - frequently loud, smelly and full, these places are islands of green that allow trees to grow to their natural size unemcumbered.  Smaller, individual garden attached to houses simply don’t have the space for this.

Trees naturally bring wildlife with them, and provide habitats for birds and insects. In short, they make places nicer, and frequently the only difference between one street and another is the level of tree planting. Estate agents report that streets or houses with trees have a higher value than areas without.  Any area described as ‘mature’ usually refers to the size and density of trees.

Trees also play a major part in absorbing particulate pollution. The large surface area of a tree’s foliage captures pollutants and when the leaves fall in the autumn the pollution is broken down into the soil. In warmer climates they reduce the need for air conditioning. They play a part in stabilising rainwater runoff as trees can absorb water and breathe it out through their leaves. They absorb sound and also generate their own through the movement of leaves. Along roads they provide screening and privacy as well as a physical boundary which protects pedestrians or divides lanes running in different directions. Lastly, wherever they are, trees are bountiful suppliers of fruit, timber and blossoms – surely something we should all have on our doorsteps.