The world’s national parks and nature reserves are thought to be worth US$600bn (€535bn, £389bn) a year, with around eight billion tourism visits annually. That income, however, is not being supported by adequate investment into heritage protection, according to the team behind the research.

A study published in PLOS Biology revealed the statistics and highlighted the need for more investment in protected natural heritage areas. Compared with the US$600bn spend generated by national parks and nature reserves, only around US$10bn (€8.9bn, £6.5bn) is spent safeguarding those sites.

According to the study by the team from Cambridge University, natural capital and the worth of natural assets – based on assigning economic value to natural environment in order to better preserve it in the future – is increasingly becoming an issue in policy making.

Protected areas cover around one eighth of the world’s land and further investment into protection of these areas could yield economic returns, as well as helping to preserve precious landscapes.

The 10 most frequently-visited sites were all in either the US or UK and consisted of:

• Golden Gate National Recreation Area, US

• Lake District National Park, UK• Peak District National Park, UK

• Lake Mead National Recreation Area, US• North York Moors National Park, UK

• Delaware Water Gap National Recreation Area, US• Dartmoor National Park, UK

• New Forest National Park, UK• Grand Canyon National Park, US

• Cape Cod National Seashore, US

To read the full study, click here.