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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Copyright 1996, The World Wide Fund For Nature