Campaigns to protect the natural world are getting more and more ambitious. The popular “30×30” movement, for example, seeks to protect 30% of Earth’s surface by the year 2030. But although there is convincing evidence that protected areas such as national parks prevent habitat loss, proof that they actually benefit wildlife is surprisingly scanty. Now, the first large study of its kind shows nature reserves can increase waterbird populations, but typically only if humans take an active role in their management.
That could be an important message for national leaders preparing to gather in China this year to set new global conservation goals. “It’s very easy for politicians to say: ‘We’ll just put some green on the map and it will be fine,’” says Ana Rodrigues, a conservation ecologist at CNRS, the French national research agency, who was not involved in the new study. But the new findings suggest “just designation is not enough. You need an adequate management.”
To understand the impact of nature reserves, conservation scientist Hannah Wauchope of the University of Exeter and colleagues decided to analyze populations of waterbird species, including ducks, geese, and sandpipers. Their primary question: Did designating a place a protected area improve the fortunes of the birds?
First, the team identified 1506 protected areas that had population data from both before and after they were created. The reserves were in dozens of countries, mainly in Europe and North America. Then, they paired each reserve with one or more control sites—a similar patch of nearby habitat—that was unprotected. This setup helped the researchers understand how the protected area influenced bird populations—and whether broader factors, such as a more favorable regional climate, had also played a role.
Next, they used a method called a “before-after-control-intervention” (BACI) analysis, which conservation scientists rarely attempt for global populations because of the large amount of data required. The analysis was so complex that supercomputers at the University of Cambridge “took forever,” says conservation scientist Julia Jones of Bangor University. Large-scale use of BACI sets this study apart, says Tom Brooks, chief scientist of the International Union for Conservation of Nature. “Conservation science has been very slow to adopt robust methods for evaluating impact,” he says. “This paper is really important in helping to advance much greater rigor.”
The researchers had hoped the analysis would clearly show protected areas benefit birds, Wauchope says. But the actual results were disappointing. Only 27% of waterbird populations in protected areas increased after the creation of the reserve, they report this week in Nature. And 21% of populations were negatively impacted, compared with the control sites, after a reserve was established. A silver lining, Wauchope says, is that nearly half the studied groups neither grew nor shrank: At least those populations were stable.
To figure out what was responsible for the population gains and losses, the team analyzed multiple factors, including the quality of national governance a reserve’s proximity to farm fields or villages, which is sometimes correlated with declining populations of wild species. Of the seven variables, they found the best predictor of success was one of the most obvious: whether the site was specifically managed for waterbirds. That could mean keeping rivers and lakes at the right levels for the protected species, removing invasive weeds, or installing fencing to keep out invasive predators, notes Taej Mundkur, a co-author and environmental conservationist with Wetlands International.
A lack of such active management might explain some of the population declines seen in the study, the researchers say. Those losses could also result from factors outside a reserve’s control, such as increasing pollution from upstream or excessive removal of water.
More benign factors could also be in play. Rodrigues points out that many reserves in Europe are small, which makes it hard for them to benefit all of the bird species that use them. A reserve in which a wetland is allowed to mature into a forest, for example, will naturally become less valuable habitat for waterbirds. “You cannot [conserve] everything in the same place, unless it’s quite a big place,” she says.
The modest success of these protected areas makes sense, says Paul Ferraro, an environmental economist at Johns Hopkins University. In many policy contexts, he notes, most interventions work no better than the status quo. The new study’s mixed results “are what good science actually looks like.” He adds: “If we’re going to answer these interminable debates about what our global conservation targets should be, we need more studies like this one. A lot more studies.”