| Good day, ladies and gentlemen. |
| I have been asked today to talk to you about the urban landscape. |
| There are two major areas that I will focus on in my talk: |
| how vegetation can have a significant effect on urban climate, |
| and how we can better plan our cities using trees |
| to provide a more comfortable environment for us to live in. |
| Trees can have a significant impact on our cities. |
| They can make a city, as a whole, a bit less windy |
| or a bit more windy, if that's what you want. |
| They can make it a bit cooler if it's a hot summer day in an Australian city, |
| or they can make it a bit more humid if it's a dry inland city. |
| On the local scale - that is, in particular areas within the city - |
| trees can make the local area more shady, cooler, |
| more humid and much less windy. |
| In fact, trees and planting of various kinds |
| can be used to make city streets actually less dangerous in particular areas. |
| How do trees do all that, you ask? |
| Well, the main difference between a tree and a building |
| is a tree has got an internal mechanism to keep the temperature regulated. |
| It evaporates water through its leaves |
| and that means that the temperature of the leaves is never very far from our own body temperature. |
| The temperature of a building surface on a hot sunny day |
| can easily be twenty degrees more than our temperature. |
| Trees, on the other hand, remain cooler than buildings because they sweat. |
| This means that they can humidify the air and cool it - |
| a property which can be exploited to improve the local climate. |
| Trees can also help break the force of winds. |
| The reason that high buildings make it windier at ground level is that, |
| as the wind goes higher and higher, it goes faster and faster. |
| When the wind hits the building, it has to go somewhere. |
| Some of it goes over the top and some goes around the sides of the building, |
| forcing those high level winds down to ground level. |
| That doesn't happen when you have trees. |
| Trees filter the wind and considerably reduce it. |
| preventing those very large strong gusts |
| that you so often find around tall buildings. |
| Another problem in built-up areas |
| is that traffic noise is intensified by tall buildings. |
| By planting a belt of trees at the side of the road, |
| you can make things a little quieter, |
| but much of the vehicle noise still goes through the trees. |
| Trees can also help reduce the amount of noise in the surroundings, |
| although the effect is not as large as people like to think. |
| Low- frequency noise, in particular, just goes through the trees as though they aren't there. |
| Although trees can significantly improve the local climate, |
| they do however take up a lot of space. |
| There are root systems to consider |
| and branches blocking windows and so on. |
| It may therefore be difficult to fit trees into the local landscape. |
| There is not a great deal you can do if you have what we call a street canyon - |
| a whole set of high-rises enclosed in a narrow street. |
| Trees need water to grow. |
| They also need some sunlight to grow |
| and you need room to put them. |
| If you have the chance of knocking buildings down and replacing them, |
| then suddenly you can start looking at different ways to design the streets and to introduce... |