1Good day, ladies and gentlemen.
2I have been asked today to talk to you about the urban landscape.
3There are two major areas that I will focus on in my talk:
4how vegetation can have a significant effect on urban climate,
5and how we can better plan our cities using trees
6to provide a more comfortable environment for us to live in.
7Trees can have a significant impact on our cities.
8They can make a city, as a whole, a bit less windy
9or a bit more windy, if that's what you want.
10They can make it a bit cooler if it's a hot summer day in an Australian city,
11or they can make it a bit more humid if it's a dry inland city.
12On the local scale - that is, in particular areas within the city -
13trees can make the local area more shady, cooler,
14more humid and much less windy.
15In fact, trees and planting of various kinds
16can be used to make city streets actually less dangerous in particular areas.
17How do trees do all that, you ask?
18Well, the main difference between a tree and a building
19is a tree has got an internal mechanism to keep the temperature regulated.
20It evaporates water through its leaves
21and that means that the temperature of the leaves is never very far from our own body temperature.
22The temperature of a building surface on a hot sunny day
23can easily be twenty degrees more than our temperature.
24Trees, on the other hand, remain cooler than buildings because they sweat.
25This means that they can humidify the air and cool it -
26a property which can be exploited to improve the local climate.
27Trees can also help break the force of winds.
28The reason that high buildings make it windier at ground level is that,
29as the wind goes higher and higher, it goes faster and faster.
30When the wind hits the building, it has to go somewhere.
31Some of it goes over the top and some goes around the sides of the building,
32forcing those high level winds down to ground level.
33That doesn't happen when you have trees.
34Trees filter the wind and considerably reduce it.
35preventing those very large strong gusts
36that you so often find around tall buildings.
37Another problem in built-up areas
38is that traffic noise is intensified by tall buildings.
39By planting a belt of trees at the side of the road,
40you can make things a little quieter,
41but much of the vehicle noise still goes through the trees.
42Trees can also help reduce the amount of noise in the surroundings,
43although the effect is not as large as people like to think.
44Low- frequency noise, in particular, just goes through the trees as though they aren't there.
45Although trees can significantly improve the local climate,
46they do however take up a lot of space.
47There are root systems to consider
48and branches blocking windows and so on.
49It may therefore be difficult to fit trees into the local landscape.
50There is not a great deal you can do if you have what we call a street canyon -
51a whole set of high-rises enclosed in a narrow street.
52Trees need water to grow.
53They also need some sunlight to grow
54and you need room to put them.
55If you have the chance of knocking buildings down and replacing them,
56then suddenly you can start looking at different ways to design the streets and to introduce...