The life of an urban tree in today’s day and age is a challenging one. Gone are the days of clean air and fresh water as a given. Space is often limited, be it for a tree’s canopy or root system. Even the soil that a tree is planted in is not always rich with nutrients. Yet we demand much from our trees, especially the ones located in urban settings. Today, we are going to look at come of those challenges.
Let’s start with a tree at its very beginning. In a forest setting, trees are born from seeds dropped or spread from the mother tree with the help from the wind, birds and other forest creatures. Many seeds reach the ground, but the challenge there is for it to germinate, survive and thrive. In an urban setting, new trees are produced from nursery stock that is planted by hand, in a pre-decided location. Sometimes that location is someone’s backyard. Other times it is on the boulevard of a busy street. In some respects that tree has a better chance of survival, as it is that much older and potentially healthier when it is planted, but there are a lot of challenges ahead for this little tree.
Let’s look at the tree that is planted on the boulevard of a busy street. The tree is planted there to give a hint of nature to our cityscapes, but its location is far from ideal for the tree. Pollution from passing cars and smog created from closed in city centres, do not make for healthy air for a tree to breathe. While they do filter out some of the pollutants and help to provide oxygen for us, air pollution can damage a tree’s leaves and photosynthesis process, as well as reduce a tree’s ability to defend itself against disease and other pests.
That same tree is hampered by space too. More specifically, by a lack of space to grow. Trees require a sufficient area for their root systems to form and develop. In urban settings, trees are often not provided with that space, resulting in stress and strain to the tree, as well as damage to surrounding sewer and septic systems, curbs, roads, walls and any other man-made structures that are nearby. The threat then becomes an insufficient base for the tree to be able to support itself, potentially resulting in it falling over and damaging the surroundings. Plus, the tree will simply not thrive.
Aside from root space, aerial space is often limited as well. I don’t know how many times I have seen trees pruned for hydro wires and it always makes me sad. While all those branches and leaves provide aesthetic appeal, when they again compete with man-made structures, the tree just seems to lose. They are hacked out for power lines, pruned off-kilter for buildings or trimmed back over roadways. That leaves less space for a tree to be able to perform its life functions of photosynthesis (remember that oxygen thing we ask trees to provide us with?). Plus, trees are left weakened from improper pruning, as well as creating stress points that can be a danger to tree collapse. Trees are also more susceptible to disease and pests when in a stressed state as well.
If that isn’t enough to contend with, urban trees are often planted in poor quality soil, are incorrectly staked (leading to damaged bark), are more prone to drought conditions (as there is less ground surface to pull water from and they are dependent on humans for watering), as well as under attack from humans ourselves vandalizing the trees that we so desperately need. Genetic diversity is often lower in urban settings, which can introduce problems when pests invade (for example, the emerald ash borer that is devastating Southwestern Ontario right now). And yet trees have been shown to improve air quality, absorb rainwater, reduce excess heat via shade, as well as reduce people’s stress levels and improve general moods. What is going on here? Trees provide us with so much and yet we throw challenges at them left, right and centre.
I think I need to hug a tree today. How about you?