The road to Parque Pumalín is festooned with dozens of whitewater waterfalls that slip down the steep cliffs into a thick forest overrun by ferns and plants with leaves as big as beach umbrellas. An active volcano threatens to wipe out the sparse human settlements that are scattered like frontier outposts, often holding populations of fewer than 100 residents. The scenery, however, suddenly changes at El Amarillo, a town of perfect picket fences, exquisitely designed bridges and hand-lettered wooden signs offering help on camping and trekking.

It is here that a 25-year experiment in environmental conservation is finally coming to fruition. Parque Pumalín is a million-acre collection of untrammelled vistas and valleys that was patched together by a pair of American conservationists whose mission, known as “wildlands philanthropy”, was to keep the lands free from industrial development.

After decades of cajoling urban residents, multinational businesses and small farmers to colonise and exploit these corners of wild Patagonia, the Chilean government has made a U-turn and announced a massive conservation campaign. Spurred by the gift of Parque Pumalín, which is the largest private donation of land to a government in Latin America, the Chilean president, Michelle Bachelet, signed an agreement to create five new national parks and join the million acres of Pumalín with 10 million acres of federal land. All this land will be placed under strict environmental protection as newly designated national parklands.

The protected areas are 5,000 times the size of Manhattan’s Central Park and include volcanoes, virgin forests and miles of wild coastline. Even the combined size of Yosemite and Yellowstone national parks would be less than one third of the land preserved by Bachelet.

Standing before glacier-topped mountains and steep granite faces reminiscent of Yosemite, Bachelet praised US philanthropists Doug Tompkins and Kristine McDivitt Tompkins for their decades-long campaign to preserve swaths of wild Patagonia. Doug Tompkins, who died in a kayak accident in December 2015, was singled out by Bachelet as a visionary who battled accusations and attempts to sabotage his conservation dream. “Doug, we did it – and I should say, we finally did it,’” said Bachelet, as she signed an accord to convert Tompkins’ private Parque Pumalín into a Chilean national park. “Today,” she said, “we are bequeathing to the country the greatest creation of protected areas in our history.”

Yvon Chouinard, the founder of clothing company Patagonia and long-time climbing partner of Tompkins, was ecstatic as he watched the announcement, noting that in a single day Chile had jumped into the ranks of countries with the highest percentage of protected lands. “That puts Chile right up there with Costa Rica in terms of the percentage of protected lands,” said Chouinard, who described the donations by Tompkins Conservation as historic. “No other human has ever created this many acres of protected wildlands [through private philanthropy] and he did not do it with the stroke of a pen. These are tourist-ready parks with trails and cabins and infrastructure.”

Kristine McDivitt Tompkins smiled broadly as she addressed hundreds of environmental activists, local residents and park employees at the entrance to the new national park. “I wish my husband Doug, whose vision inspired today’s historic pledge, were here on this memorable day. Our team and I feel his absence deeply,” she said. “National parks exist in almost every country in the world. God knows what form they are in, but they exist everywhere. Some of them are battered, some are ill-funded, probably most. But they exist. And by and large, that holds the firmest, most consistent possibility for longevity in terms of terrestrial conservation.”

The audience applauded wildly as she described the conservation accord as a crucial first step towards uniting Chilean national parks in what will be known as “the route of parks”. “This is unprecedented and will become one of the most famous routes in the world, connecting up communities and bringing new economic activity to each region. There is no long-term conservation possible unless neighbouring communities find that their best interests are served. National parks have proven to be a strong source of national pride, creating honour and admiration throughout their citizenry.”

With foreign tourism booming in Chile, the route of parks concept is expected to consolidate what today is a haphazard and largely unorganised tourist circuit stretching for 2,400km from the city of Puerto Montt in the north to the Beagle Channel astride Tierra del Fuego in southernmost Chile. “National parks are the gold standard of conservation,” said Hernán Mladinic, who spent years working to persuade the Chilean government to preserve intact ecosystems in southern Chile. “For every dollar you invest in national parks, you get 10 back; it’s more profitable than copper.”

Facebook Twitter Pinterest Douglas Tompkins and Kristine McDivitt Tompkins spent 25 years working to save wild habitat and ecosystems in Chile and Argentina. Photograph: Tompkins Conservation

The transition from private park to national park will be incremental over the next two years as Chilean government officials seek to maintain the aesthetics and design with which Tompkins infused Parque Pumalín.“Today is the beginning of a roadmap for the creation of 10 million new acres of national parks under the patrimony of the Chilean national park service with a level of beauty and integrity that Doug hoped would raise the whole concept of what national parks mean for the Chileans and what national parks mean for the world,” said Rick Ridgeway, vice president of public engagement at Patagonia clothing company and a long-time climbing partner of Tompkins. “His dream was to inculcate this sense of pride into the Chileans and into the citizens of the world.”

Employing an American concept known as “wild and scenic highways”, the new parks will seek to implement a design aesthetic that includes scenic lookout points, artfully designed signage and attempts to have roads follow the contours of the land rather than ripping straight lines through the rugged terrain.

Facebook Twitter Pinterest Parque Pumalín. Photograph: 2007 Linde Waidhofer

While there was no opposition to the announcement of the new park, Tompkins had long faced bitter resistance. Local politicians accused him of harbouring secret plans to kick settlers off their land or create a dump for radioactive material. Others alleged that Tompkins planned to create a Jewish homeland or wanted to breed a mixed-race beast by crossing African lions with Patagonian pumas to attack local livestock. “I remember a local farmer saying that Doug flew his plane so low that it wouldn’t be hard to wait on the hillside with a Mauser and shoot it down,” said Laura Casanova, a hotel operator in El Amarillo, who knew Tompkins for some 20 years.

While his relationship with Chilean authorities was rocky at times, both Tompkins and his partner Kris found wide success across South America. In Argentina they worked closely with the national government to create Monte Léon national park and had several other large-scale projects reaching completion including Iberá National Park in Corrientes.

In Argentina, Kris Tompkins oversees programmes to reintroduce endangered species including jaguars, giant anteaters, peccaries, tapirs and pampas deer. Known as “rewilding”, the programme has been extremely successful as species on the brink of extinction, including the pampas deer and the giant anteater, are now thriving.

“What I would like to do is change the way national parks look at rewilding everywhere in the world where there are extirpated [locally extinct] species and make it one of the goals of national parks everywhere, to rewild,” she said. “As they say, landscape without wildlife is just scenery.”

The Chilean move stands in stark contrast to the policies of US president Donald Trump, who has rejected global warming, plans to slash the budget of the US Environmental Protection Agency and is seeking to reverse preservation accords signed by the Obama administration.

“It is not just US citizens who have to resist Trump and the influence of extreme right-wing Republicans and the intrinsic selfishness, blindness, anti-science, anti-environment attitude that have recently gotten the upper hand in the States,” said Lito Tejada-Flores, a renowned mountain climber and photographer who was a lifelong friend of Tompkins. “I find it very encouraging that we have some smart leaders in South America – on both sides of the Andes – who have said ‘Yes, conservation is important and science is real’.”