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Peter H. Raven


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ountains occupy a fifth of the Earth's land surface but contain only a tenth of its human population [1], making them refuges for many of the planet's rarest animal and plant species and wildlife habitats. Yet these refuges are increasingly threatened by advancing landuse changes, and, potentially, by changing climate patterns. [Add]

The movement of ecological zones

As the world warms, climatic zones rise up mountain sides, dragging ecological zones with them. The species associated with them occupy ever smaller areas ever further uphill until, eventually, even the mountain top becomes too hot for some and they disappear altogether. [Add]

Mountains are vital economic and ecological resources, high in biodiversity and minerals alike. Their height triggers heavy precipitation which, coupled with the water-storing capacity of glaciers, gives them a vital hydrological role. Mountain regions are the sources of most of the world's major rivers and half the world's population is reliant on mountain water. A billion Chinese, Indians and Bangladeshis drink from rivers flowing out of the Himalayas. In arid countries such as Egypt, mountain sources provide more than 90 percent of the available water [2].

Their elevation allows mountains to harbor a great diversity of species and habitats within a small area, often forming islands of biodiversity that take their own evolutionary path and create high levels of endemism, such as in the Peruvian Andes. More than half the world's endemic bird species occur in tropical mountain regions [3]. Mountains also provide natural refuges for species during times of climatic change and stress.

Mountain terrain has deterred dense human occupation, for cities have nowhere to spread and access is difficult. Mountain communities have traditionally been isolated, developing particular skills to survive -- such as transhumance pastoralism and cutting terraces on hillsides to protect soils, conserve water and provide flat land for cultivation. But such communities have often remained poor and at the margins of society. Mountain nations such as Bhutan, Lesotho, Nepal, Rwanda, Burundi and Ethiopia are among the poorest 20 in the world [4]. Within nations, mountains are often home to tribal groups and other minorities, such as the Tibetans, the Quecha in the central Andes and the Kurds in Turkey and Iraq. While some such groups find themselves increasingly marginalized, there are also opposite trends towards social and economic integration with the lowlands.

In countries with land shortages and growing populations, lowlanders may invade hill regions, causing deforestation and cultivating erosion-prone soils. Areas containing tropical mountain forests have had the fastest rates of both annual population growth and deforestation in recent years [5]. Examples include the Guatemalan Highlands and the Bolivian Altiplano. [Add]

Elsewhere, mountain regions are being abandoned by farming communities who tire of the meagre earnings and hard work. This is as true in developing countries such as Peru as in the European Alps and Pyrenees. Abandonment does not necessarily reduce environmental degradation but may increase it. Left untended, terraces on steep hillsides swiftly start to crumble away.

But mountains have other attractions for lowlanders. Some contain valuable minerals. And many are scenically beautiful, enticing skiers, mountaineers, trekkers and environmentalists, and offering alternative livelihoods to local communities. The Alps accommodate 100 million visitor-days a year. In the Himalayas, more than 250 000 pilgrims and trekkers climb to the Gagotri glacier, sacred source of the River Ganges, each year.

[mountain ranges]

[population density]


The impact of tourism on ecosystems can be double-edged. On the one hand, ski slopes and roads have to be constructed, water and fuelwood found, and rubbish disposed of -- all of which can cause environmental damage. On the other hand, there is an economic incentive to protect the wildernesses many come to see -- and the revenue to accomplish it. [Add]

World Heritage

A natural World Heritage Site may exemplify a stage of the world's geological or biological evolution, or contain the natural habitats of endangered animals. It may be a scene of exceptional beauty or a reserve for large numbers of wild animals. A cultural monument may be a masterpiece of creative genius or have exerted great architectural influence, or it may be an outstanding example of a certain culture. There are some 630 sites overall, 150 of which fall within or near mountain regions, representative of both the historical and natural value of mountainous areas and the qualities that attract millions of tourists every year. [Add]

Valleys within mountain ranges have their own vulnerabilities. They become transport arteries and sites for urban development, where the surrounding mountains can trap urban air pollution. Valleys are also attractive sites for building reservoirs to supply water, generate hydroelectricity or provide flood protection. But reservoirs not only flood valleys and disrupt fluvial ecosystems, they also force displaced inhabitants into the hills, where they may cause further environmental damage. The Three Gorges dam currently being constructed on the River Yangtze in China is expected to displace up to 3 million people into surrounding hills. [Add]

Mountain ranges often become zones of conflict, particularly as many contested national borders run through them, for instance in Kashmir. Mountains also play host to disputes between national governments and ethnic minorities such as the Chechens in Russia, the Kosovans in Serbia and the East Timorese. Their rugged terrain may serve to house refugees from such conflicts as well as providing sanctuary for guerrillas and outlaws. Two thirds of the 34 armed conflicts in the world in 1993 took place primarily in mountain areas [6].

Such conflicts may protect the environment by discouraging organized development and inward migration. But they may equally encourage illegal and environmentally destructive activities, such as logging. In Liberia, Cambodia and the Thai-Myanmar border region, intensive logging helped fund warring groups in the 1990s. Virtually all the world's heroin and cocaine comes from three small mountain regions: on the borders of Pakistan-Afghanistan, Myanmar-Thailand-Laos and Bolivia-Colombia, causing massive deforestation and soil erosion [7]. [Add]

Mountain ecosystems face a massive test of their robustness from projected climate change. Warming is already melting many glaciers, fundamentally altering hydrology both in the mountain regions and downstream. For instance, glaciers cover 17 percent of the Himalayas and provide two thirds of the flow of the River Ganges. But at their present rate of decline all the glaciers in the middle and eastern Himalayas will have disappeared by 2035. Many mountain valleys are threatened by floods as lakes formed by melting ice are breached [8]. [Add]


Steep hillsides washed by heavy mountain rains are vulnerable to soil erosion and landslides, especially when vegetation is removed for logging, agriculture or roads. On virgin hillsides, landslides create gaps in forests that can encourage biodiversity [9]. But in inhabited areas, they are dangerous to local populations and may lead to floods.

When Hurricane Mitch hit Honduras in October 1998, some 8 000 people were killed in floods and landslides. Much of the damage was attributed to deforestation and land disturbance caused by road and house construction and mining activity in its mountainous interior. Since 1960, the population of Honduras has quadrupled while its forested area has fallen from 63 percent to 37 percent. The national population density -- at 51 people per square kilometer -- remains comparatively low, but urbanization in mountainous areas maximizes the number of people at risk in a disaster [10].

While land disturbance incontrovertibly causes localized erosion and landslides, there is less scientific agreement about whether these activities cause downstream problems in large catchments. Deforestation in the Himalayas is frequently accused of causing siltation in northern India and Bangladesh. But there is evidence that most eroded material is deposited locally rather than transported over long distances [11]. [Add]

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