Environmental Engineering Reference
In-Depth Information
(a)
(b)
800
0.5
700
0.4
600
0.3
500
0.2
8 species
4 species
2 species
400
0.1
300
0
3
2
1
0
1
2
3
Number of species
Decreasing functional group richness
Fig. 1.6
(a) Primar y productivity (expressed as above-ground biomass at the end of the growing season) of European
grasslands composed of two, four or eight species - note that productivity is somewhat higher when there are more species.
However, in cases where all three functional plant groups are represented (grasses, forbs and nitrogen-fi xing legumes)
productivity is substantially higher than where only two or one of the functional groups are represented. The functional
groups differ in the way they garner and convert radiant energy, water and plant nutrients into biomass. (After Hector et al.,
1999.) (b) Rate of decomposition of tree leaves that fall into a stream is greater when larvae of three species of stream-
shredding stonefl ies are present, in comparison to just two or one species. The same total number of stonefl y individuals is
present in all cases. (After Jonsson & Malmqvist, 2000.)
Beyond the academic quest to understand biodiversity and its role in ecosystems,
a utilitarian view of nature focuses on the services that ecosystems provide for
people to use and enjoy.
Provisioning services
include wild foods such as fi sh from
the ocean and bushmeat and berries from the forest, medicinal herbs, wood and
fi ber products, fuel and drinking water. Then there are
cultural services
that nature
contributes to human well-being by providing spiritual or aesthetic fulfi llment and
educational and recreational opportunities.
Regulating services
include the ecosys-
tem's ability to deal with pollutants, the moderation by forest and wetland of dis-
turbances such as fl oods, the ecosystem's ability to reduce pests and disease risk,
and even the regulation of climate (via the capture or 'sequestration' by plants of
the greenhouse gas carbon dioxide). Finally, there are
supporting services
that under-
lie all the other services, such as primary production (by plants), the nutrient cycling
upon which productivity is based, and soil formation.
Different ecosystems, both relatively pristine and human-engineered, provide
their particular blends of ecosystem services (Figure 1.7). In the case of three 'pro-
visioning' services - production of crops, livestock and aquaculture - human activi-
ties have had a positive effect. And in recent times, because of increased tree
planting in some parts of the world, there has been an improvement in the seques-
tration of carbon by trees (a 'regulating' ecosystem service).
But humans have degraded most of the other services. There have been adverse
effects on 'provisioning' services in capture fi sheries, timber production and water
supply (because forest ecosystems moderate river fl ow, so forest loss increases fl ow
during fl ooding and decreases it during dry times). We have also seen reductions
in many 'regulating' services, including the soil's capacity to detoxify manmade
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