If you’ve seen a neighbourhood built in the 1990s or the 2000s, all the streets line up, with the same trees planted at equal intervals. Every March, these trees blossom together, looking like a green-screen postcard for your city.
This ideal has dominated urban planners’ vision of what a perfect estate should look like. A one-species or monoculture field brings symmetry and predictability that is appealing to human psychology.
But this isn’t how things work today. Many towns no longer allow their municipal foresters to plant a single species throughout the community. Why have they changed their mind? Because a “cookie-cutter” assembly line approach to planting trees is an ecological ticking time bomb waiting to happen. For a range of Wholesale Plants, visit https://www.palmstead.co.uk/wholesale-plants-for-trade-in-kent
The threat comes from insects and diseases. There have always been insects and diseases in trees but it seems like new ones emerge every year. Emerald Ash Borer, for instance, was unknown until a few years ago; now it has wiped out more than 80% of the Ash trees in the US. This creates a massacre overnight. The only silver lining of such ecological disaster is the awakening call to many towns. It took millions to heal the damage that Emerald Ash Borer caused and people will never think of the beauty of planting a single tree family at the same place again.
There is another factor to consider. We can’t control everything around us. That might seem an odd statement, since our society is constantly trying to control nature, whether by building seawalls or managing wildlife. But the natural world simply doesn’t cooperate. Insects and diseases are opportunistic: if you create an opportunity for them to spread, they will take it.
Dutch Elm Disease is a good example. The disease requires only one tree to get started, so a single tree in your garden could be all the bacteria needs to begin an invasion. If you plant several elms on your block, then you’ve just created multiple points of entry for Dutch Elm Disease. If you try to prevent the disease in some parts of your city by giving those areas a different tree, you’ll find that you need a lot of other kinds of trees. You would end up with 10 or 15 different tree varieties to keep each neighbourhood limited to the monoculture standard.
The problem is that there aren’t that many tree varieties to choose from. And even if there were, it’s doubtful that these alternatives would provide the same range of benefits, such as size, fall colours and flowering season, that the original trees delivered.
Finally, the biggest issue might not be the number of tree varieties available but the fact that we simply don’t know which insect or disease will strike next – or what hosts it will affect.