Scotland's two national parks encompass some of the country's most celebrated landscapes and attract almost five million visitors a year.

But their popularity - combined with heavy rainfall - is threatening to scar the very scenery they were established to protect.

Walkers and mountaineers flood to the Loch Lomond and the Trossachs and the Cairngorms national parks throughout the year, but experts have warned the considerable number of people and the wet weather have been damaging the habitat and causing scarring to the landscape.

A project set up to bring together the two national park authorities to address the serious threat of man-made erosion to paths across areas of outstanding natural beauty has now been given a major financial boost, with the Heritage Lottery Fund (HFL) announcing its initial support for a grant of £3.28 million.

The People And The Mountains project will see 41 eroded upland paths, covering a distance of 77.36 miles, restored and upgraded. It will train young people with the skills to gain employment and work with schools and volunteers to preserve Scotland's great outdoors.

Colin McLean, head of the HLF, said: "Nature lies at the very heart of what makes Scotland special and its beauty attracts and ever-growing number of walkers, climbers and tourists each year. Although this is a significant boon to our tourist economy, we need to ensure it does not damage the special environment so many have come to enjoy.

"Our natural heritage offers a rich resource for skills and education so the Heritage Lottery Fund is delighted this project will offer training to many young people. Their newly-learned skills will make a positive difference to their lives, and play an important part in looking after the future of Scotland's magnificent landscapes."

Loch Lomond and the ­Trossachs and the Cairngorms national parks were created in 2002 and 2003 respectively by an Act of the Scottish Parliament. They cover an area 36 times the size of Glasgow, from Ben Lomond to the lochs of the Trossachs; and from the Cairngorms Plateau to the banks of the River Spey.

The competing demands of environmental protection and housing development have often brought controversy.

But it is recognised they sustain the vital tourist industry and the wider economy, as well as contributing to the health, welfare and recreation of the nation.

Cairngorms, which includes five of the UK's highest mountains, is home to 25 per cent of Britain's threatened species.

Loch Lomond and the ­Trossachs National Park includes 61 Sites Of Special Scientific ­Interest and eight Special Areas Of Conservation for the protection of rare habitats and species, such as the golden eagle, peregrine, ptarmigan and mountain ringlet butterflies.

Speaking about the funding boost, Dougie Baird, chief executive of the Cairngorms Outdoor Access Trust, said: "This is fantastic news for the partnership behind this project, and will allow us to develop a project that directly involves the people of Scotland in the care of the priceless mountain assets within both our National Parks."

Cairngorms National Park Authority and Access Trust board member Gregor Hutcheon said: "The Park Authority is immensely proud of the work and efforts of Cairngorms Outdoor Access Trust and this significant funding will allow them take forward this innovative and exciting project that will have real benefits for visitors and land managers."

The boundaries of the Loch Lomond and Trossachs park have stayed the same since its creation. But in 2010 the southern boundary of the Cairngorms National Park was extended to include parts of Highland Perthshire, including Blair Atholl, Killiecrankie and Glenshee.