Ian Spellerberg : trees in urban environments – we should not make choices that abuse nature!

trees in urban environments

'Kowhai Flower' photograph by Jan Van Goethem #jan.v.g #kowhai



We take them for granted but we can’t do without them. Trees provide us with food, timber, shelter and pleasure. Most importantly the green leaves and shoots of trees produce oxygen and at the same time take away the carbon dioxide. We need trees to stay alive. How many trees do you think is required to keep one person supplied with oxygen? There are various estimates but most seem to agree that about 20 trees are required to extract carbon dioxide and to produce oxygen for one person. What are the implications of that number?  At the very least it shows how important trees are for humans. So next time someone says how silly it is to “hug a tree”, remind them how much we owe to trees. Try it, close your eyes and hug a tree. Feel the bark with your finger tips and smell the sweetness of the tree trunk. Keep your eyes closed and say the first words that come into your head!  Hugging a tree is as good as any meditation or stress relieving activities. I am proud to be a tree hugger.

City trees

Most cities and towns around the world have trees alongside the streets and in parks. Trees in urban environments have many benefits. They help to cleanse the air by soaking up pollutants and of course provide oxygen. Have you ever compared urban air with that in a natural subalpine forest? Try and make that comparison some time. The air tastes and smells quite different where there are plenty of trees and you can’t help but fill your lungs with air that’s purified by nature. Just think about those people who live in in cities without trees. Where does there oxygen come from? It must come from far away but as it crosses the city it combines with dust and pollutants. Trees in urban environments help to dampen the noise of traffic. Trees provide shade in summer and of course can just look nice.

Choosing trees

Trees in urban environments don’t just happen to appear. Someone has made a decision to plant the trees and someone or some group of people has made a choice. The question is therefore what criteria are used to choose trees for streets and parks?  The most common criteria are safety, health, availability and the species of trees already in place. For a very long time the choice of tree species was made on engineering grounds. Trees that damaged roads, pipes and footpaths were quite rightly avoided. Trees that tended to drop their branches or grew too large or blocked visibility were not suitable. Similarly trees that had messy fruits or trees that caused allergies were considered not suitable. Over the last few decades, the criteria used for selecting trees for urban environments has been chosen not just by engineers but also landscape architects. Design, sense of place, and signature plantings were all fashionable. The look, the texture and the colour of trees all add up a perception of how beautiful a trees looks.

What is interesting is that for many years, councils have established lists of trees thought to be unsuitable for planting along streets and in parks.  Surprisingly very few councils have established lists of trees that are suitable. So, trees in urban environments have, for a very long time been, chosen on the basis of safety, health, nuisance, design and beauty, what is already planted and in the end what is available from tree nurseries. No wonder so many towns and cities have non-native trees.

Safety and health have to be the first criteria. After that, trees for urban environments should be chosen using ecological and sustainability criteria.

Towns and cities develop and expand over time and in doing so native plants are destroyed to make way for buildings and infrastructure such as roads, pavements and car parks. All too often there is no attempt to restore any of the native plants. On the contrary and to add to the ecological damage, exotic tree species are planted! What’s wrong with that? What is wrong is that such an approach works against nature. It’s an approach that is human orientated, selfish and arrogant. Ecology and sustainability are not considered. That is we need to consider ecological systems and ecological communities when choosing trees. We need to consider sustainable use of nature.

Why exotic trees are not a good choice for nz urban environments:

  1. Many exotic trees to nz are deciduous. There is an annual cost for clearing up autumn leaves and dealing with blocked drains (as well as the cost of people slipping of leaves and being injured).
  2. Exotic trees take up space at the expense of native vegetation.
  3. Single specimens of exotic tree species do not make ecological sense. It’s like expecting a single violinist to play Beethoven’s 5th Symphony. Just as members of an orchestra interact so do trees in their ecological communities. They have evolved to interact with other native wildlife and it’s the ecological interactions that provide a much richer diversity of nature than single trees.
  4. Exotic trees have not evolved to live in their new locality. Their true potential can’t be achieved.
  5. Exotic trees species can become invasive and damage the indigenous wildlife. The cost of dealing with invasive species is huge.
  6. Choosing exotic species is going against nature – it’s abusing mother nature.


Why native or indigenous tree species are a good choice for urban environments.

  1. It’s an opportunity to offset the vast areas that have been cleared of native vegetation.
  2. It’s an opportunity to contribute to the conservation of native tree species.
  3. It’s an opportunity to be proud of and show off our natural heritage.
  4. It’s an opportunity to apologise to nature for the way humans have destroyed so much of the indigenous plant communities.
  5. Native trees will help support other native wildlife including native birds and insects.
  6. It’s an opportunity to try and weave natural tree species communities into the urban environment.

The last of these reasons has not been done before. That is attempt to replicate the natural distribution and relative abundance of native tree communities in the urban environments. In nature, different trees species occur at different frequencies and in different distribution patterns. That is some species are naturally few in number and are widely scattered. Other species are very common and grow in groups. How exciting it would be to try and copy these numbers and patterns within the urban environment! That would be the ultimate in unselfish behaviour and show that urban environments can be interwoven with nature.

The exceptions
In my opinion, native trees should always be the default choice for any town or city. There are exceptions and they relate to social and environmental sustainability. The exceptions could be trees that provide nuts and fruits.  Community gardens are important ingredients for social interaction, education and learning about the limits of nature. Exotic fruit and nut trees are an exciting way of promoting social and environmental sustainability.

What can you do?

  1. Hug a tree.
  2. Learn about native trees and see if there are native trees in and around your workplace, school or recreational area. If not what would you do about it?
  3. Write to your local council and ask that native trees be the default position.
  4. Write a letter to your newspaper.
  5. Be part of a local or national nature organisation.
  6. Write to your member of parliament. They are there to serve us.
  7. Have courage to support native plants!


In New Zealand the best resource for native plants is the web site for the New Zealand Plant Conservation Network.

There are many very good books about native trees.


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