Governments around the world have created parks and reserves to protect endangered species and ecosystems from humans. However, strict rules can be politically controversial so policymakers would like to know how much more the environment is protected by applying these restrictions. Popular wisdom suggests that the more restrictive the rules are the better but there is little empirical evidence to support this logic.

Empirical evidence is necessary because popular logic can be thwarted by politics. Some governments may choose to apply strict rules to the most threatened ecosystems but previous studies suggest that many do not because it is politically costly to do so. Instead, they apply the more restrictive rules to less valuable – and thus less threatened – ecosystems. The gains from stricter rules may therefore be small.

Using data from four tropical countries, we compared the reductions in deforestation in strictly and less strictly protected rainforest areas. To consider whether more protection is more protective, we answered two questions. First: "Did strictly protected areas show less deforestation than less strictly protected ones?" The answer (see the red bar in the figure) is affected both by the severity of the rules applied and the threats in the areas in question. Second: "Was more deforestation prevented in strictly protected areas compared to less strictly protected ones?" The second question separates the effect of restrictions from location (see the green bar in the figure).

Although stricter rules are often associated with less deforestation, the differences are not always huge and can arise from differences in location. In Costa Rica, for example, more strictly protected areas show much larger reductions in deforestation than less strictly protected ones (the red bar), but this effect comes from differences in location rather than how severe the protection is. If the same areas were less protected, the change in deforestation that is observed would have been small and not statistically much bigger than zero (the green bar).

Each country is of course different but the punchline is simple: stricter rules are not necessarily better. To help them make better decisions regarding conservation, policymakers need more evidence from more countries and on more parameters, including social parameters like poverty.

The team reported the study in Environmental Research Letters (ERL) as part of the ERL Focus on Delivering on Conservation Promises.

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