As the summer sunshine melts the last of the snow on the highest pistes of the Schiltalp - above Murren in the Bernese Oberland - yellow arnica, little black vanilla orchids, elegant white St Bruno's lily and many more flowers appear. Both the winter snow and the summer flowers have their aficionados. You could, though, be forgiven - if the quantity of ski holiday brochures are anything to go by - for assuming that skiing is overwhelmingly more popular than Alpine walking.

Yet in the Austrian Alps the tourism split is 40 per cent in summer and 60 per cent in winter. In the Swiss Alps, roughly 12 million non-Swiss occupy hotel beds in summer and 9 million in winter.

Skiing is the audacious alpine holiday newcomer. When Dr Paulcke, a German physician, and a young apprentice named Branger - both from the then Swiss summer resort of Davos - bought Finnish skis at the Great Exhibition in Paris in 1889, no one could have guessed what their purchases would lead to.

Within a few decades, the high peaks that had once been the reward of a half day's climb could be skied five times before lunch. But it was not until the 1960s that purpose-built ski resorts attracted mass winter tourism and winter holidays started to rival the summer tourist trade.

Today the Alps have more than 40,000 ski runs and 14,000 ski lifts. Austria's runs alone, if joined end to end, would circle the globe.

Building more and more pistes, plus the attendant cable cars and hotels - and roads, water and electricity supplies to service them - is, according to many conservationists, damaging the fragile alpine environment and jeopardising the summer alpine tourist industry.

Dr Jim Thorsell, Senior Advisor for Natural Heritage at the Geneva-based International Union for the Conservation of Nature, points to the stark contrast between the purpose-built resort of Cervinia in the Italian Alps and Zermatt in Switzerland, each on opposite sides of the Matterhorn.

"Cervinia," says Dr Thorsell, "is architecturally insulting. The slopes have been bulldozed excessively to re-contour them so that, in summer, they look ugly. Large areas are devoid of vegetation and the soil is eroding. Power lines make it even worse."

The developments at Zermatt, on the other hand, are much more sensitive to the local environment, and downhill ski runs haven't done too much damage to the vegetation.

The Austrians are probably the most concerned about over development. In Voralberg Province, no new ski developments, nor extensions to existing facilities, are allowed. In Tyrol Province, the environmental implications of any developments have to be thoroughly assessed, though there is no ban on new facilities if their impact is minimal. Other Alpine Austrian Provinces have also tightened their downhill grip.

In the Swiss Alps, too, new developments get the go-ahead less often. In the Bernese Oberland, summer tourism is more valuable than ski revenues, so developments which disfigure Alpine vistas are taboo.

Forest felling to create more pistes is not allowed in the better cared for parts of the Alps. Spruce forests are natural avalanche barriers. Where they have been felled, huge sums of money are having to be spent constructing barriers on steep mountainsides to protect villages below.

Cows, complete with bells, still graze the high meadows in summer, yet many former dairy farmers have exchanged cheese making for more lucrative ski-tuition jobs or for running boarding houses and shops in villages lower down the slopes.

In the Swiss Alps, less than 10 per cent of the resident population lives in the mountains. A century ago it was 25 per cent. In the Italian Alps many farms have been abandoned.

So the traditional Heidi image is under threat. So, too, are the colourful Alpine meadows. Abandoned, many of them lose their superb colours as scrub - which grazing formerly kept in check - encroaches. Insects, including many gorgeous butterflies, are also declining. And avalanche risk increases when meadows are abandoned. "Uncut meadows are more slippery, especially in spring when large, wet flow avalanches occur," says Dr Walter Ammann, Head of the Swiss Federal Institute for Snow and Avalanche Research. "This is because the snow bends the long grass over and can slip off it. Cut meadows have a short vegetation stubble to which the snow grips," he adds.

The highest government subsidies, to help keep farmers up in the mountains, are paid by the Swiss. A 45-hectare Alpine farm (the average size) gets around pounds 20,000 a year. Few farmers would otherwise consider staying on. A similar French Alpine farm might get half that. Little wonder that the village of Tour in the Chamonix Valley now has 30 diary cows (all on the single remaining farm) yet in the 1940s had 250.

In a recent speech, Prince Sadruddin Aga Khan, Chairman of Alp Action, drew attention to the Alpine Convention, signed in 1991 by the six Alpine states. This recognises a common responsibility for the protection and sustainable development of the Alps. Unless this spirit of co-operation is enhanced, unless Alpine farmers are better supported, and until environmental awareness of the impact of more and more ski facilities by some governments is increased, it isn't only the spectacular Alpine scenery which will suffer. Tourism revenues will plummet faster than a slalom.