Wildlife experts have warned that nearly half of the world's tropical forest reserves are unable to properly protect wildlife due to degradation.
The researchers also pointed out that even well-protected tropical reserves may not protect wildlife if the surrounding habitat is degraded.
"Biodiversity is declining rapidly at reserves including Kahuzi Biega in the Democratic Republic of Congo, Xishuangbanna in southern China, and Northern Sierra Madre in the Philippines, among others," said William Laurance, research associate at the Smithsonian Tropical Research Institute now at James Cook University in Australia.
Laurance asked experts who study plant and animal life across the Americas, Africa and Asia-Pacific to rate the effectiveness of the reserves where they have worked over the last two to three decades.
Smithsonian co-authors include STRI staff scientist Joe Wright, and John Kress, Mercedes Foster and Louise Emmons at the National Museum of Natural History. They rated reserve health based on changes in abundance of 31 different groups from trees to primates.
"Reserves are like arks for biodiversity. But some are in danger of sinking," said Laurance.
Even well-protected reserves mirror changes in surrounding landscapes. On the Smithsonian's Barro Colorado Island research station in Panama researchers recorded slight increases in exotic animals and plants.
Reserves suffering the most were those were encroached upon by illegal colonists, hunters and loggers. The bottom line, researchers said, is that we need to do a better job of protecting protected areas.
The results were published in the journal Nature.