Ecology and Ecosystems
Mountains support a rich variety of plant and animal life.
Mountain ecosystems represent islands of biological diversity
surrounded by a sea of lowlands, often developed for agriculture
or urbanised. Climate change will place additional stresses on
these already fragile mountain environments. Many species will
be vulnerable to warming because the possibilities for migration
to new areas are limited. The only direction to migrate in a warmer
world is up.
A general biogeographical rule of thumb is that a 500 metre rise
in altitude corresponds to a 3oC drop in temperature.
We know from studies of past environments that plants respond
to a warming climate by migrating to higher latitudes or altitudes.
In the Andes, for example, vegetation zones have shifted upwards
by 1,0001,500 metres since the height of the last ice age,
and the topmost, coldadapted zones have vanished.
Global temperatures are now higher than at any time since then,
and rising. The implication is that mountaintop species
will dwindle, and could ultimately go extinct.
The threat is greatest for those species which are already rare
or endemic to a limited area. As many alpine plants fall into
this category, the impact on biodiversity will be significant.
In the European Alps, 15 per cent of the endemic plant species
are confined to the highaltitude alpine belt.
Snow protects alpine plants from frost in winter and provides
water for their growth in spring. A reduction in snow cover, therefore,
will have an adverse affect on highaltitude plant communities.
As these communities are often found at mountain summits they
will be lost and replaced by subalpine or montane ecosystems.
This has been confirmed on 40 Alpine summits in Austria, Switzerland
and Italy by Professor Georg Grabherr of the University of Vienna
and colleagues, whose ecological observations show that there
has been an increase in the number of species present, as one
would expect to find if species from lower altitudes invade the
plant communities higher up.
The same effects can be seen to apply to animals. The arctic fox
population in the alpine zone of the Fennoscandian mountains,
for example, has fallen dramatically while the number of red foxes
has grown. Continued warming in this and other arcticalpine
regions, like the Scottish Highlands, for instance, could have
an impact on the distribution and numbers of species which shelter
in snow or have white camouflage, such as the ptarmigan or the
snow hare.
In the Italian and southern French Alps a warmer and drier climate
would lead to the invasion of more southerly, Mediterranean tree
species in the submontane belt. This would be less likely
to happen in the more humid climate at the eastern end of the
range.
Warmer and drier summers mean more forest fires. Forests in the
European Alps, the Blue Mountains of New South Wales, the coastal
mountains of California and Mount Kenya are all at risk from an
increase in fires, and some are in close proximity to suburban
populations. Los Angeles and Sydney suburbs, for example, have
both experienced outofcontrol forest fires in recent
years.
Mountain environments represent both an important scientific resource
and a spiritual sanctuary far from human disturbance and pollution.
Yet unspoilt mountain landscapes have become fewer and fragmented
by economic development, rendering already fragile ecosystems
as islands vulnerable to migrations and species extinctions. Global
warming has raised a new and menacing threat to an environment
that is less able to accommodate rapid changes because of past
and ongoing degradation.
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