The Ecosystem
What is an ecosystem?
An ecosystem is a piece of nature. Nature with plants, animals, microorganisms, water, wind, minerals and more. An ecosystem can consist of land, water and air. There are no fixed boundaries as to how large or small an ecosystem is, or how old or young an ecosystem may be. It is up to the beholder to decide the scales of time and space that shall apply. An ecosystem can for example be either a small lake or a large ocean. It can be the life on a tree stump during one summer or a forest that burns down, grows back over 200 years and then burns down again. Sometimes the whole planet earth, including the atmosphere is described as one huge ecosystem. Some call this 'global-ecosystem' Gaia.
Figure 1: A theoretical diagram of the phases an ecosystem goes through.
The Holling figure of eight: a model ecosystem
C.S Holling has attempted to describe an ecosystem with help of a theoretical model. His theory is that an ecosystem never finds itself in a stable position; instead it goes through four different phases. We take a forest here as an example of an ecosystem. Phase 1 consists of an area being colonised by different organisms and beginning to take it's form. Phase 1 passes into phase 2 when the organisms, in this case the trees begin to grow. This phase may take place over a long period of time and the thickening forest is often seen as fairly stable. However, in reality the forest is highly sensitive to disturbances. There is, for example, a large amount of wood that could easily catch fire. When this happens, and according to Holling it will, there will be a powerful blaze that takes the forest into phase 3, the release phase. After the disturbance, in phase 4 there is a reorganisation. At this point the nutritive substances and areas liberated by the fire are requisitioned by new species. The ecosystem consequently goes into phase 1 again. For the 'new' ecosystem to maintain the same functions as the previous one there must be a sufficient diversity of organisms and functions in phase 4 (reorganisation). Holling calls this type of diversity, which guides the ecosystem towards the same functions as before, 'ecological memory'.
Production of goods and services
An
ecosystem produces renewable goods such as fish, crops, timber and
drinking water. This type of production from the ecosystem is fast,
often replenished yearly and is found essentially all over the world.
An
ecosystem can also produce non-renewable goods such as crude oil,
gold and diamonds. The production of non-renewable goods is extremely
slow and often limited to certain types of ecosystem with very specific
characteristics. The production of non-renewable goods can be the
result of a process that has taken place over millions of years.
Ecosystems
also support society via ecological services. There are a great
number of examples of these. Some of the most important are the
cycling of nitrogen, phosphorus and water. Bacteria and other microorganisms
in the earth and water also serve a function by ensuring that we
have fertile soil, trees for timber and fishable waters. Further
services are carried out by birds when they eat pests and vermin
thus keeping the forests in check, likewise the insects when they
pollinate our crops year after year, all for free. Trees and other
plants perform a service vital to life when they turn carbon dioxide
into oxygen. They thereby maintain the atmosphere's composition
and ensure that we are able to breathe. Wetlands and other ecosystems
perform many services such as dealing with our refuse by, for example,
cleaning sewage. Furthermore, we have the healthy ecosystem to thank
for the wonderful sights of nature when on holiday and for the richly
coloured autumn walk with a basket of mushrooms.
Biological diversity: an important service
Ecosystems also have the capability to sustain biological diversity. This particular service is important in many ways. It is, for example, important to have different types of organisms because they fulfill differing functions in the ecosystem, both in terms of time and space. The existence of animals that eat other animals is essential, likewise the existence of bacteria which break down decaying leaves. These species, which have primary responsibility for certain functions in the ecosystem, are often called key stone species. But even other species, which presently seem to serve no particular function, are important. They must exist so that they may step into the place of a key stone species if it should die out for some reason. Such species act as a sort of buffer and ensure that the ecosystem survives fires, earthquakes, storms and other natural disturbances. These species will probably become all the more important in a future with larger and more evident manmade disturbances, such as the greenhouse effect, reduction of the ozone layer, the spread of disease and overexploitation of forests, agricultural areas, fishing waters etc.
Resilience: A weapon against the ecosystem's instability
A popular
concept that describes the buffer capacity of an ecosystem is the
term resilience. A resilient ecosystem is one that has the capability
to deal with disturbances (both natural and manmade). This ability
to buffer against disturbances is important because all ecosystems
have an inbuilt uncertainty. This uncertainty is perhaps the most
difficult aspect to comprehend concerning nature and how it works.
We are used to always strive for control. However, it is impossible
to have control over an ecosystem, for example to predict how much
maize or fish will be produced next year. We can't even say exactly
what weather we will have tomorrow! This uncertainty depends not
on a lack of data or information. Rather, the ecosystem's inbuilt
characteristics (it is complex, self organised and dynamic) mean
that we will never be able to predict how the ecosystem of the future
will be.
By
maintaining the ecosystem's capacity to cope with disturbances we
are at the same time preserving it's capability to supply us with
the products and services we are dependent upon. Resilient ecosystems
give us accordingly the possibility to build an existence or society
suitable to a certain type of local environment. With resilient
ecosystems there is a reduction in the uncertainty and it becomes
easier for us to 'do the right thing' and benefit from nature in
a way that is both long term and sustainable.
Flexible management
In order to deal with the instability within ecosystems we must adapt our management of natural resources and make it flexible. We must learn to both read and understand changes in nature such as fires and drought and consequently be able to cope with these 'surprises' through a well-prepared insurance strategy. In other words, the management must also possess some sort of buffer capacity.
L. Hård af Segerstad, K. Böttiger Bille och C. Holmlund
(000119)
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