The study, carried out by the World Conservation Union (IUCN) with the support of Conservation International (CI) and local partners, also found that preserving the highland route - called the Gran Ruta Inca in Spanish - could have important benefits for ecosystem and watershed maintenance, as well as ecotourism and community development.
"The historical, social and even spiritual importance of this ancient wonder of engineering demands that the international community seriously study the establishment of protected areas along the route," said Miguel Pellerano, the IUCN's regional director for South America. "By protecting the Gran Ruta Inca we can also safeguard some of the hemisphere's most fragile ecosystems and habitats."
The route runs through 15 distinct ecoregions, including four that are considered Endangered: the Peruvian Yungas, the Marañon Dry Forest, the Chilean Mattoral and the Chilean Winter Rain Forest. It also cuts through some of the last remaining habitat of the spectacled Andean bear, the Andean condor and the vicuña - South America's smallest camelid that was almost hunted to extinction in the 1960s and 1970s.
The study found that revitalizing the Gran Ruta would also help reintegrate thousands of indigenous communities that live along the route and reinforce traditional conservation practices rooted in Andean beliefs about the sacred dimension of nature.
The Gran Ruta Inca, called Capaq Ñan in Quechua, was the main north-south highway of the Inca Empire, stretching 7,000 km from its northernmost point to its southernmost. Clinging to the side of the Andes mountain range at altitudes ranging between 1,000 and 4,500 meters, it is monumental in scale, reaching 15 meters wide in some areas.
The route starts in southern Colombia and runs through Ecuador, Peru and Bolivia before forking into Chile and Argentina. If the 8,500 km of trail were laid out end-to-end, the Gran Ruta would stretch from Cape Town, South Africa to southern France. In addition, some 30,000 km of lateral roads branch off of it, including the world-renowned Inca Trail, which leads from near the empire's spiritual capital in Cusco, Peru to the iconic ruins of Machu Picchu.
Today, less than half of the route has been formally surveyed, but much it is thought to be damaged by road construction, development and neglect. And despite its historical importance, none of the Gran Ruta's 8,500 km route is formally protected. However, it does intersect eight separate protected areas, providing coverage of about 422 km of the route - or about 5 percent.
"The Gran Ruta Inca presents a unique opportunity to rally support around a strategic system of protected areas, many locally managed, that will benefit biodiversity conservation, historic preservation and the indigenous communities that live along the route," says Stephen Edwards, CI's Andean tourism specialist. "Traditionally, these communities have lived in some of the most marginalized areas on the continent; an initiative like this, and its incredible potential for community-based tourism, could lead to powerful and positive transformations of the region."
Along with keeping ancient traditions and culture alive, the communities play a critical role in maintaining plant and crop diversity, or agrobiodiversity. An important subset of biodiversity - and the foundation of global food security - agrobiodiversity in the Andes is unparalleled. Local farmers grow more than 3,000 varieties of potatoes, 2,500 varieties of quinoa and 1,000 different kinds of corn. The region also produces 20 species of food plants on which most of the world depends. But this resource is being threatened by the influx of commercially grown and genetically modified seed, as well as the breakdown of the Gran Ruta Inca, which was the backbone of traditional seed-sharing practices.
Careful management of areas along the highland route - especially in Ecuador and Peru - is also critical for the watershed. The highlands absorb vast amounts of water during the rainy season that is released in steady streams throughout the year, supporting local agriculture and helping control landslides, which can be devastating along the steep flanks of the Andes.
"Creating a series of protected areas that recognize the Gran Ruta's historical importance and help reestablish the traditional ties that existed between communities along the route would be invaluable to the region and the world," explains IUCN's Pellerano. "The Quechua, Aymara and other communities that live along the route have a long history of venerating and respecting nature. A project like this could help preserve those ancient conservation practices as a living lesson to all of us."