Natural World Heritage Sites (NWHS), via the formal process run by UNESCO (United Nations Educational, Scientific and Cultural Organisation), are globally recognised as containing some of the Earth's most valuable natural assets.
Researchers, including those from the University of Queensland in Australia and Wildlife Conservation Society (WCS) in the US, looked at human pressure over time using the global Human Footprint criteria, which includes roads, agriculture, urbanisation and industrial infrastructure, along with forest loss.
The most impacted NWHS were found in Asia, including Manas Wildlife Sanctuary in Assam, Chitwan National Park in Nepal, and Simien National Park in Ethiopia.
Keoladeo National Park in Rajasthan was subject to the highest levels of human pressure of any NWHS.
More From This Section
In terms of forest loss, highly impacted parks included the Rio Platano Biosphere Reserve in Honduras, which lost 365 square kilometres (8.5 per cent) of their forest respectively, since 2000.
Even celebrated places like Yellowstone National Park in the US were impacted, losing some six per cent of its forests.
"World Heritage natural sites should be maintained and protected fully. For a site to lose ten or twenty per cent of its forested area in two decades is alarming and must be addressed," said James Allan, from University of Queensland.
"Any place that is listed as a World Heritage site is a globally important asset to all of humanity," said James Watson of the University of Queensland.
"The world would never accept the Acropolis being knocked down, or a couple of pyramids being flattened for housing estates or roads, yet right now, across our planet, we are simply letting many of our natural World Heritage sites be severely altered," Watson said.
"Urgent intervention is clearly needed to save these places and their outstanding natural universal values," he said.
Some NWHS such as the Sinharaja Forest Reserve and Mana Pools National Park showed minimal change in forest loss or human pressure, but the authors say they are in the minority.
The research appears in the journal Biological Conservation.