Introduction
12 000 years ago human beings were hunter/gatherers constantly on the move looking for food, their numbers limited by the amount of food they could find. Then came a revolution!
People of the new stone age (the Neolithic Culture) learnt that they could grow crops and domestic animals. They no longer needed to be constantly foraging and hunting and food could be stored. They were able to live less nomadic lives and had time to develop other skills. We see the development of settlements beginning and a rise in population numbers as humans began to dominate their environment.
Where does everyone live today?
At the beginning of the new stone age the world's population was estimated to be about 5.5 million. Now it is over 6500 million.
So where do all these people live? Over half of them live in urban ecosystems, crammed into a tiny part of the world's land surface (about 5%). Humans and human-made structures dominate these ecosystems. So is there any room for green spaces and wild-life in theses urban areas? Surprisingly yes - look at the table to see how much green space there is in some of the UK 's largest cities.
| City | Population figures according to the 2001 census |
Percentage of the total urban area which are (government statistics 2003) |
|
|---|---|---|---|
gardens |
all green space |
||
| London | 7 138 236 |
24 |
38 |
| Birmingham | 970 892 |
29 |
35 |
| Liverpool | 469 017 |
22 |
32 |
| Leeds | 443 247 |
11 |
71 |
| Manchester | 394 269 |
20 |
36 |
As far as we know, in 1800 London was the only city in the world with a population of more than a million. Today there are hundreds of cities with a population of more than a million. See the Atlas of 20th century urban growth for more information.
Urban habitats - what about the plants and animals?
In these green spaces you will find many of the habitats you would expect to see in the countryside such as grassland and woodland, and even freshwater and coastal habitats. Gardens and allotments can contain several habitats all concentrated into a small area. Recolonisation of wasteland can lead to the development of particularly interesting areas with a great variety of living organisms (a high biodiversity).
There are some surprises too - look out for the cliff-nesting birds which have adapted their behaviour and use ledges of high rise buildings. Others species like the peppered moth have adapted physically to some of the special conditions found in urban ecosystems.
The common toad
The challenges of city living for plants and animals
Living in an urban ecosystem can provide challenges for wildlife. Here are just some of the problems which might have to be overcome
- Large areas of soil are covered by impermeable materials which interrupts the flow of water through the ecosystem.
- Pollution levels may be high.
- Plant roots often encounter physical barriers.
- There are changes in microclimate e.g. increased temperature and changes in light.
- Sites might be temporary. There is often a high degree of disturbance of the soil and surface plants.
- Alien species (ones which wouldn't naturally be found in Britain) are often introduced. Similarly others like stinging nettles (not liked by some humans) may be removed.
- Many habitats are isolated and small. This may make it difficult for species to colonise new sites or to complete their breeding cycle. This common toad, for example, needs to move from dry land where it hibernates to wetland where it mates and lays its eggs - not always an easy journey in a city!
Are green spaces a luxury in the urban ecosystem?
No - they are vital to the health of the city and its people. They help to:
- control temperature
- filter and clean the air
- absorb moisture and control water flow
- reduce noise levels
Green spaces are essential to wild life too. The urban ecosystem is one of the few ecosystems in the world which is rapidly expanding. It is generally agreed that it is the small towns and cities particularly those in less economically developed countries that will grow most leading to the disappearance of more and more of our wild and rural areas
Urban green spaces are going to become increasingly important to wild-life. It's vital that we understand and conserve them.
