Definition and history

The term ecosystem, a contraction of the words ecological system, is really just a way of thinking of all the components, living and inanimate, of a geographically-defined environment as a single system.

An ecosystem can be as small as a pond or as large as a rainforest, you can even build your own in a garden or fish tank. Humans create larger ecosystems too, either agricultural or urban and have certainly had an effect on natural ecosystems, often a very damaging effect.

Groups of similar ecosystems are called biomes; for example, the Arctic Tundra is considered a biome and the world's largest biome is the open sea.

The term was first defined in Arthur Tansley's 1935 paper, The Use and Abuse of Vegetational Concepts and Terms. Tansley was expanding on the work of fellow British botanist Arthur Clapham whom he had asked to coin a term to cover both the physical and living parts of an environment.

Ecosystems are analysed and studied as unique entities. This study is a complex as the systems themselves. However, all ecosystems feature an energy input such as the sun's heat which keeps life in the system going. Living organisms are classified into hierarchical food chains and webs and water, oxygen, carbon, nitrogen and phosphorous cycles are studied too.

Types of ecosystems

Ecosystems are most often classified by the type of vegetation that predominates and the climate area in which they are found, for example, tropical rain forests are classified as, ''tropical ombrophilous forests'' according to the Unesco Vegetation Classification System, just one of the classification systems ecologists use.

Biomes - geographical areas of similar ecosystems - can be split into six types: freshwater, marine, desert, forest, grassland and tundra.

These can be further divided.

Freshwater ecosystems are: ponds and lakes; streams and rivers and wetlands. Wetlands include bogs, swamps and marshes and contain the most species of any of the planet's ecosystems.

Marine ecosystems are: oceans, coral reefs and estuaries. The oceans are the world's largest ecosystems and are considered to cover the shore as far as tidal waters come in.

Desert ecosystems are: hot and dry deserts, semiarid, coastal and cold. While we often think of deserts and heats as synonymous, parts of the Arctic and Antarctic are classified as deserts because of their low rainfall.

Forest ecosystems are: tropical, temperate and boreal. Tropical forests include the great rainforests, which, with their incredible diversity of species and importance as carbon sinks are a focus for environmentalists. Boreal forests, also called taiga, are the largest biome on land.

Grasslands are: tropical (or savannas) and temperate. Temperate grasslands include the great American prairies and the Russian steppe.

Tundra ecosystems are: arctic and alpine.

WWF and National Geographic have classified the world into 867 ecoregions (essentially ecosystems) and you can find detailed profiles of them all here.

Preserving ecosystems

All ecosystems change; they are dynamic, living things. However, human activity has done a great deal to damage the planet's natural ecosystems, through pollution, exploitation of natural resources and even (the often well-intentioned) introduction of outside species.

The environmental and conservation movements have, over time, widened their focus from single species preservation to recognition that the complexity of nature means that the environment as a whole must be protected. The growing study of and awareness of biodiversity has encouraged this holistic approach in the green movement.

The United Nations Convention on Biodiversity (UNCBD), which was unveiled at the so-called Earth Summit in Rio de Janeiro in 1992, includes an 'ecosystems approach' to conservation, recognising the complexity of preserving the natural world while allowing humans to live sustainably.

The UNCBD studies ecosystems to try and determine their value, for example, this study looks at forest ecosystems.

This approach has also led to the recognition of what we take from natural ecosystems, so-called ecosystem services, for example forests provide us with timber, which is an extractive use, but may also provide economic activity as a venue for ecotourism. Governments who have signed up to the UNCBD should be taking this approach to their efforts to conserve the environments in their country.

Climate change and ecosystems

Ecosystems are dynamic and changing within themselves and are also subject to the action of outside forces, not least of all climate change. As we have seen climate and vegetation are the prime definers of an ecosystem and changing climates can exaggerate the damage done by other damaging inputs into systems, such as pollution and destruction of habitats. Climate change could change an ecosystem's type, and current research focuses on how to avoid this.

Natural ecosystems could also play a role in stopping some of the harmful effects of climate change. Plants store carbon, keeping it out of the atmosphere, so ecosystems, and there has been a particular focus on the great rainforests as carbon stores, are a natural defence for our future.

Ecosystems under threat

As we have seen, all ecosystems change, but we are adding to natural processes with the way we live. Such is the state of human impact on the natural environment that almost all natural ecosystems can be seen to be under some sort of threat.

Scientists are learning to study (study of ecosystem collapse in a North American lake) these changes and pushing for action to protect ecosystems both as the home to some of the planet's most threatened species and to give human beings a sustainable future on the planet too.

WWF has listed the 35 ecosystems it thinks are most under threat and most important to save. Tragically, so much damage has been done to the world's environment; they have had to focus on preserving what is left, including what they describe as ''the largest and most intact representative of their ecosystem''.

The list covers most of the planet and includes some areas we will all have heard of as well as less well known ecosystems.

The ecosystems identified by WWF are:

The best surviving rainforests: the Amazon, the Congo Basin and the New Guinea rainforest. The rainforests with the most species too, which are the western Amazon and the rainforests of northwest South America.

The environments of New Caledonia, Fiji, Vanuatu, South Africa, southwest Australia and Madagascar are selected because of the large numbers of rare native species still surviving.

These Rivers have been chosen because of the richness of life they support: the Amazon, Orinoco, Congo, Mekong, Yangtze, and the New River of southeast USA.

The Namib-Karoo-Kaokoveld Deserts and Chihuahuan Desert are listed as unique environments with a high diversity of species. The grasslands, savannas and woodlands of central and eastern Africa, central and eastern South America and North America are also selected for the wide variety of life they support, while the Eastern Himalayan grasslands are the world's tallest and remain strongholds of endangered tiger and rhino species.

Montane ecosystems are found in mountains, below the tree line, and WWF names the Himalayan montane and the Albertine Rift forests of Africa's Great Rift Valley as the two it is most important to save.

The threat to coral reefs is well known, with ghostly images of once teeming and hyper-colourful environments reduced to lifeless skeletons an all too vivid illustration of a damaged ecosystem. WWF has selected those reefs which support the most diverse life and they are: the Coral Triangle, Great Barrier Reef, New Caledonian reefs and those of Fiji and East Africa.

Finally, the seas on which we should focus our conservation efforts are, according to WWF, the most productive: the Arctic, Southern Oceans, and the seas around West Africa.

What can you do?

You can, if you are lucky enough to have your own garden, create your own ecosystem.

It goes without saying that you should do what you can to limit the damage you do to ecosystems by avoiding polluting as far as you can. While you may be far away from some of the most vital and threatened ecosystems, the western consumer lifestyle's tentacles show little regard to these distances and the products we buy may be damaging ecosystems on the other side of the world. Become an informed consumer and try to buy products which do as little damage to the planet as possible.

Most environmental campaigns and charities now focus on ecosystems and you can help protect them by joining with others to raise money or simply to help get your voice heard by decision makers. If your government is a signatory of the UNCBD (and most are) then they should be doing work to protect ecosystems - as them what they are doing and if they're doing nothing ask them why not.