To find out if terrestrial protected areas are effective in achieving their environmental and socioeconomic goals, we read 56 scientific studies. (See the interactive infographic below.)Overall, protected areas do appear to reduce forest cover loss. But other ecological outcomes of protected areas, like biodiversity or illegal hunting, remain extremely understudied.The evidence on socioeconomic impacts is very thin. What limited rigorous research exists shows that protected areas do not exacerbate poverty generally, but anecdotal studies suggest that protected areas could be making other aspects of people’s well-being worse off.This is part of a special Mongabay series on “Conservation Effectiveness”. In 1986, Patricia Wright, then a budding primatologist, spent weeks combing the rainforests of eastern Madagascar in search of the greater bamboo lemur (Prolemur simus), a five-pound bamboo-eating primate that was feared extinct. It was only once she stopped over at a hotel in a small village for a night that her luck changed. Behind the hotel was a river, and across the river was a majestic rainforest where Wright spotted not only the greater bamboo lemur, but another species of bamboo lemur that was unknown to Western science. The discoveries were exciting. But droves of loggers were moving into the rainforest with axes to cut down the grand old trees and ship the wood to Europe — legally, it appeared. Worried that her beloved lemur-filled forest would soon be gone, Wright approached the director of what is now the Ministry of Environment, Ecology and Forests and pleaded her case. “The director told me that when he gave the timber concessions he didn’t know there was a new species to science and a rediscovered species in the forest,” Wright, now at Stony Brook University in New York, U.S., told Mongabay. “But now I was there to tell him that this forest is very special and should be protected.” To her surprise, the director suggested turning the forest into a national park, but only if Wright arranged the funds for it and did most of the legwork herself. Over the next five years, Wright raised more than $5 million and carved out the boundary of what would soon become Ranomafana National Park in consultation with people who lived around the forest. Finally, on May 31, 1991, the park was officially inaugurated with elders from 57 nearby villages attending the ceremony. Wright had gone in search of a lemur, but she had helped create a protected area. Twenty-five years later, Ranomafana National Park looks like an island of dense green being choked by waves of deforestation from all sides. “I know for sure that the rainforest wouldn’t exist today had it not been for the national park,” Wright said. “The north of the park, for instance, was all forest when we started. It’s all gone now.” National parks like Ranomafana and other protected areas have long been considered the one-stop solution to conserving terrestrial biodiversity and forests. They are seen as conservation success stories. But what happens after you create a protected area? Does establishing a protected area on paper really “protect” a forest? Do a park’s plants and animals thrive because of their forest home’s new legal status? And what happens to the people living in and around the park? We tried to find out by reviewing some of the scientific literature that looks at the effects of this popular conservation strategy.