Nature preserves: A line on a map is not enough

What happens in Vegas may stay in the center of sin ‘n sleaze, but what happens outside nature preserves often filters inside, according to a monumental study in this week’s Nature online.

The report is yet more evidence that lines on a map are not enough to preserve essential biodiversity.

The decline of tropical reserves threatens the broad range of living forms that has evolved over the eons. As changes like deforestation and conversion to agriculture continue to kill off endangered species, parks and nature preserves must serve as “island arks,” capable of sustaining the forms of life.

But these arks are under threat from inside and out.

Although plenty of studies have looked at internal threats, less was known about conditions outside the borders, says William Laurence of James Cook University in Australia. The new study presents systematic evidence, based on interviews with more than 200 local experts, on conditions around 60 protected areas in 36 tropical nations.

“We’ve shown that the outside pressures — ‘the eternal external threat’ — really is having a serious impact on the biodiversity of many tropical protected areas, and on a global scale,” Laurence wrote us.  “This is quite different from, say, inferring that such things might be going on from localized studies of fragmented ecosystems.”

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Instead of poring over countless studies describing different reserves at different levels of detail, Laurence and his collaborators chose to consult experts on reserves that had been the focus of at least 10 published research studies. “Interviews were far more efficient,” he wrote.  “We initially tried to do this by reviewing scientific papers, but it took a great deal of time, and most reserves just don’t have enough published research to make all the assessments we wanted.”

Instead of focusing on birds, bats, plants or mammals, the study looked at the health of “functional groups,” such as apex (top) predators, large-seeded old growth trees, primates and birds that eat insects in the lower portion of the forest.

Such groups are “really the only basis for comparison if you’re trying to understand trends across different continents,” Laurence wrote.  “Groups like ‘apex predators’ occur everywhere, but a single species such as a tiger, say, occurs only in Asia.  Functional groups are the common currency we can use for broad-scale comparisons.”

Although changes caused by fires, illegal mining, water pollution and livestock grazing tend to be more intense inside reserves, the impact of “change outside and inside the reserves are roughly equivalent, at least in statistical terms,” Laurence says.  “The changes happening outside of protected areas seem to be having comparable impacts on the health of biodiversity.  What this means is we can’t just designate parks and then assume all will be okay; we must pay keen attention to the broader landscapes surrounding protected areas.”

“External and internal threats tend to be correlated, often strongly,” Laurence wrote.  “Parks tend to reduce the intensity of threats, but they also tend to be leaky, allowing some of those threats to penetrate inside.  What you do on the outside of parks really matters, because it’s also typically happening on the inside, to a lesser degree.”