Environmental Engineering Reference
In-Depth Information
of soil degradation is loss of the soil biota and thus the loss of 'free' ecosys-
tem services that biodiversity provides. These 'free' services and functions on
which agriculture depends include soil formation, nutrient cycling, mainte-
nance of hydrological cycles, and pollination of crops.
Ecosystem services need to be factored into decisions about land use. For
example, a patch of remnant vegetation may provide more than aesthetics,
shade and shelter. It is removing carbon dioxide, producing oxygen, using
water, and may have some role in controlling watertables, and the movement
of wind and water over the surface of the land. At present, we tend to exclude
these services in cost accounting for agricultural production.
How ecosystems function
The cycles and processes we observe within natural landscapes result from the
functions and interactions of the many elements, both living and non-living.
These processes, such as the recycling of carbon, nitrogen and phosphorus, the
hydrological cycle and the transfer of energy, as well as the slower processes of
weathering and erosion, all rely to varying extents on the functional role of
plants, animals and microbes. In stable ecosystems, supply and demand
balance these cycles so that few resources are either lost or accumulate.
Individual organisms, from bacteria to large trees, function for their own
survival and reproduction and also play a functional role in wider ecosystems.
For example, in performing the functions necessary for its own survival, an
annual grass contributes to processes such as soil stabilisation, nutrient and
water cycling, providing habitat for ground dwelling animals and food for mil-
lions of other living things such as decomposing bacteria or herbivorous
insects. The more biodiverse an ecosystem, the more complex the interactions
of the functional roles, producing an overall functioning ecosystem much
greater than the sum of its constituent parts. Similarly, reduction in biodiver-
sity can safely be assumed to impair the overall functioning of a natural system
and on a scale much greater than the sum of parts removed.
As biodiversity is lost, ecosystems become less complex. This initiates a
cascade of events that result in long-lasting changes. Simplified ecosystems
become less resilient. They are less able to absorb environmental shocks and
disturbances while continuing to maintain their original levels of function,
such as rates of growth, transpiration, fixation and uptake of nitrogen.
Reducing biodiversity means that there are fewer components to buffer the
blows inflicted by drought, fire, exotic species and climate change.
