1. The World Now Protects 15% of Its Land, but Crucial Biodiversity Zones Left Out
https://www.iucn.org/news/secretariat/201609/world-now-protects-15-its-land-crucial-biodiversity-zones-left-out
2. Protected Planet Report 2016,2016
3. Economic Values of Protected Areas: Guidelines for Protected Area Managers,1998
4. Sustainable Tourism in Protected Areas: Guidelines for Planning and Management;Eagles,2002
5. Protected areas, conservation and tourism – financing the sustainable dream