By James Cove BBC News

Environmental groups are concerned about expansion

There has been a spate of mergers as resorts link up with each other to try to become the biggest.

This season the massive French resorts of La Plagne and Les Arcs were joined together by a double-decker cable car to create one of the world's biggest ski areas with 250 marked runs served by 175 lifts.

It went ahead despite a long-running campaign by environmental groups.

Big is best

Plans have been unveiled this week to link the Swiss resorts of Engleberg, Hasliberg and Melchsee-Frutt to create an area with 210 kilometres of runs served by 51 lifts.

Eight new chairlifts would need to be built and a ski tunnel.

Ecosign Mountain Resort Planner, a Canadian Development Company, has carried out an initial survey and estimates it would cost 37m euros and take 10 years to complete.

In Italy, the two regions of Vallee d'Aosta and Piedmont have been linked by a modern new cable car that can transport more than 800 people per hour.

In the Pyrenees, plans have just been released for the giant Andorran ski area of Grand Valira to extend over the border to join up with the French resort of Porte Puymorens.

It would involve the construction of a new resort base with hotels, apartments and all the associated leisure and shopping facilities.

"The first question skiers and snowboarders ask is how many lifts does the resort have and how many kilometres of runs,"says Katie Joly from Crystal Holidays, the largest British tour operator.

Environmental concerns

"The resorts have to meet that demand or people will simply go elsewhere".

Any construction in the mountains has significant environmental repercussions.

The building work alone requires huge amounts of raw material and it all has to be taken up the mountainside - usually in lorries.

The mountains are not a playground for people Giles Privat, Mountain Wilderness

Many of the resorts are the size of small towns using vast quantities of energy and producing large amounts of refuse.

"The mountains are not a playground for people. They are a natural resource that should be respected and preserved," Giles Privat from the environmental group, Mountain Wilderness told BBC News Online. "We build in them at our peril".

Strict controls

Many ski resorts though go to great lengths to protect the environment.

The French resort of Les Gets, in the Portes du Soleil, has had a large programme of lift building in recent years but all have been constructed on the same route as existing lifts so as not to harm the environment.

"We have one of the prettiest ski resorts in the world so if we damaged that by building lifts everywhere and chopping down trees we would harm our product," says Les Get's Resort Director, Flora Richard.

"It is good business sense for us to be environmentally aware".