Other studies have made similar discoveries around the world from India to Japan to South America, Salick said.
"While sacred sites are not created for biodiversity conservation, they still contribute to protection of ecosystems and conservation," Salick said.
A different approach to conservation is needed to support such sites as biodiversity refuges, she added. The old style of conservation placed people as the enemy of protection efforts.
"(In the old approach), humans had to be extracted from nature to conserve nature. This is just the opposite," she said.
Historically, the Three Sisters Caves served as refuges from slave traders and during tribal conflicts. They were also used for traditional ceremonies and religious practices, said study lead author Kristian Metcalfe of the University of Exeter in Penryn, Cornwall.
Metcalfe, with the permission of elders from a local village, surveyed parts of the caves, crawling through the guano and cockroaches to catalog the caves' species.
His study, published in the journal Oryx, revealed that the caves and their surroundings house 121 species of plants, including nine considered somewhat rare.