The sites which are designated for special protection as areas of outstanding importance for nature, are at risk worldwide from activities including oil and gas exploration, mining and illegal logging.
The report, produced for the conservation charity WWF by Dalberg Global Development Advisors, shows how natural World Heritage sites contribute to economic and social development through the protection of the environment, but also details global failures to protect these areas of outstanding universal value.
The report cites the Selous Game Reserve in Tanzania, which it says has experienced damage due to oil and mineral extraction as well as road construction, and now faces additional threats from hydropower construction.
"Selous once contained globally significant populations of African elephants, hippopotamuses and critically endangered black rhinoceroses. However, the site faces continuing threats from oil and mineral extraction, which have been exacerbated since 2009 following the relaxation of the legal framework that protects Tanzanian game reserves," says the study.
"The Tanzanian government has already awarded at least 50 concessions for oil, gas and mining extraction that
overlap with the site, and new tenders for petroleum blocks in Selous are still being considered."
In 2012, the boundary of the World Heritage Site was modified to enable the construction of a large-scale uranium mine in the southern area of the reserve.
"These activities have damaged the site’s biodiversity and caused a reduction in revenue from tourism activities. This resulted in local job losses for people who were affected by declining tourism and were not equipped with the right skills to work in oil exploration or mining," says the report.
The site also faces threats from the proposed construction of a hydropower plant, which would result in flooding of parts of the reserve and the loss of terrestrial habitats, according to the study.
"These harmful industrial activities, some of which have been undertaken within the same area, have increased access to the site and led to further damage from poaching. Access roads constructed by Shell in the 1980s for oil exploration, and by ARMZ for uranium mineral extraction, have facilitated access to Selous for poachers," says the study.
The company responsible for operating the new uranium mine in the excised area of the property conceded that “poachers took advantage when we built a road to the deposit.”
Since its inscription in 1982, Selous's elephant population has fallen by almost 90 per cent, and now just over 11,000 elephants remain within the reserve.
Additionally, almost the entire population of critically endangered black rhinos has been lost since the site’s inscription. Wildlife poaching has jeopardized the reserve’s outstanding universal value and, as a result, the site was inscribed on the List of World Heritage in Danger in 2014.
According to the study, 114 natural and mixed World Heritage sites out of 229 either have oil, gas or mining concessions overlapping them or are under threat from at least one other harmful industrial activity.
“Conserving the environment does not hurt economic opportunities, it allows us to build sustainably on these irreplaceable assets,” said Roberto Troya, WWF’s Director for Latin America and the Caribbean.
“Threats to World Heritage sites in places as diverse as Belize, Spain and Tanzania demonstrate how widespread the risks run and should unite us in our effort to protect these essential areas.”
The WWF findings are far higher than the 18 natural sites listed as "in danger", a more severe condition, by the World Heritage Committee of the U.N.'s cultural agency UNESCO.
"This is staggering. We're trying to raise a flag here," Marco Lambertini, director general of WWF International, told Reuters. "We're not opposing development, we're opposing badly planned development."
The WWF study said that more than 11 million people depended on the heritage sites for food, water, shelter and medicine.
Lambertini said that the economic value of nature was too often ignored, even though the sites created jobs, for instance from ecotourism worth billions of dollars. "Nature continues to be taken for granted," he said.
The study expands on a report by the WWF last year that said about a third of sites were threatened by mining and oil and gas. It adds threats such as over-fishing, harmful logging and disruptions of water supplies from dams.
It urged companies to obey U.N. appeals to declare all heritage sites "no go" areas for oil and gas exploration, mines, unsustainable timber production and over-fishing.