Our Environment - Mining and the Environment: From Ore to Metal - page 307

case in low relief, mid-continental areas, where climatic conditions differ little over large
distances. Plant and animal species living in these environments, which are usually quite
uniform and lack the variety of special habitats or niches that encourage the evolution of
new species, are generally widely distributed. An example is the Mulga Woodland which
occupies much of the arid zone of central and Western Australia.
By contrast, in the adjacent high mountains, elevation and aspect combine to produce
marked variations in temperature and rainfall which, with differences in geological substrate
that are also characteristic of mountains, result in numerous habitat differences, supporting a
much greater diversity of species, some of which may have relatively limited distributions.
Tropical rainforests generally support very high diversities of plants and animals,
largely because biological productivity is very high and the structure of the forest, in itself,
provides a wide variety of habitats and micro-habitats, each of which supports a differ-
ent assemblage of species. While most tropical rainforest species are common with wide
distributions, this is not always the case. In particular, some species have become rare or
endangered as a result of exploitation by man. Examples are the great apes of Africa, the
Indian tiger, many species of commercially valuable timber trees, parrots and cockatoos
popular as caged birds, and numerous orchid species. And, of course, some previously
common species are now uncommon because the forest habitat on which they depend, has
been largely removed. High diversity is, however, not restricted to tropical rainforests. For
example, the heathlands of southwest Australia support a very high diversity of plants,
many of which have very limited distributions, based on adaptations to subtle differences
in substrate conditions. Several large mineral sand mines are located in this environment
which poses particular challenges to rehabilitation.
Islands, particularly remote oceanic islands, are at the other extreme from mid-
continental areas. Individual islands commonly have highly distinctive assemblages of
flora and fauna, with relatively little overlap of species between islands, except where
they are in close proximity. Species and sub-species may be endemic to a single island or
group of islands. This high degree of endemism is particularly pronounced in the central
and eastern islands of Indonesia. Plants and animals endemic to islands are also particu-
larly vulnerable to invasion by introduced species. Accordingly, the potential for species
extinction as a direct or indirect result of mining, is relatively high on small or medium
sized islands.
Finally, uncommon or unusual habitats, particularly permanently moist areas in other-
wise arid environments, may support remnant populations of plants and animals that were
widespread during different, usually wetter periods, but which have contracted to one or
more refuge areas, as the climate has changed. Examples are ferns which are confined to
permanently shaded areas at the bases of cliffs in central Australia. These relict species may
expand their distributions again when cooler or wetter conditions return. The geological
record contains many examples of extensive expansion and contraction in areas occupied
by species as a result of fluctuating climatic conditions. In fact, it appears that the climate
has seldom, if ever, been static for long and accordingly, the distributions of species are
constantly changing in response to climate change, and these changes can be quite rapid.
It follows from the foregoing, admittedly oversimplified bio-geographic summary that
the risks to biodiversity from mining, or any other invasive activity, will depend on the
bio-geographic situation as much as on the nature of the activity itself.
To understand how biodiversity is likely to respond to mining, impacts at each level of
diversity are best assessed in terms of composition (what biological units are present and
how abundant they are), structure (or pattern) (how biological units are organized in time
and space) and function (the role different biological units play in maintaining natural
processes and dynamics) as illustrated in Table 7.3 .

Tropical rainforests generally
support very high diversities of
plants and animals.

The potential for species
extinction as a direct or indirect
result of mining, is relatively high
on small or medium sized islands.

The risks to biodiversity from
mining, or any other invasive
activity, will depend on the
biogeographic situation as much
as on the nature of the activity
itself.