Geography Reference
In-Depth Information
because many plants have been found to have important pharma-
ceutical benefits for us and if they are 'lost before they are found'
then their medical uses will never be discovered. The elimination
of species by direct slaughter and over-killing by humans for food,
highly priced animal products such as ivory and whale oil, or to
remove pests has led to major modifications of the animal kingdom.
Slaughter by humans can be on an enormous scale. For example, of
the 60 million bison on the Great Plains in 1700 only 21 indi-
viduals remained by 1913.
Half of the Earth's forest cover has been removed by humans.
Deforestation commenced several thousand years ago, accelerated
by the development of the axe. The emergence of domestic live-
stock encouraged the clearing of land for agriculture, fuel needs
grew and protection from enemies was realised through removal of
hiding places in forests. Deforestation has progressed across differ-
ent zones of the Earth and its current focus is now in the tropical
forests. Large amounts of carbon are stored in the biomass of the
tropical forests. Unlike in temperate forests, the nutrient store is
mainly above ground and so even if the trees are removed and used
for furniture (and hence the carbon is still on land) then the nutri-
ents have been taken out of the forest and the ecosystem will be
severely depleted. It also seems that the tropical forests have helped
absorb some of our carbon dioxide emissions from fossil fuel
burning, acting as a buffer against climate change and thus their
removal also destroys this buffer (see Chapter 2).
It has been suggested that there are hotspots on the land surface
where biodiversity is particularly high. Work by Norman Myers
and colleagues has suggested that 44 per cent of all species of vas-
cular plants are found in 25 hotspots comprising only 1.4 per cent
of the land surface. Surprising areas are included as hotspots; the
natural vegetation of the tropical Andes seems to be the most
diverse hotspot. Even though its vegetation has been reduced to 25
per cent of its original extent by human action it still contains 6.7
per cent of all plant species in the world and 5.7 per cent of all ver-
tebrate animals. Myers and colleagues urge that these hotspot areas
be singled out for the attention of conservationists, to attempt to
protect them. It is also notable that climate change projections
suggest that all of these hotspots will undergo considerable warming
in the next 100 years.
