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In The Lorax, Dr. Seuss’s classic children’s conservation parable, after an entrepreneur comes to town and chops down all the tufty truffula trees to make onesies, he gets fully reamed out by the Lorax, a creature who “speaks for the trees.” Cutting down the trees has a spiral of bad effects on the fantasy environment—including giving the frolicking animals called Bar-ba-loots a disease called the crummies.

In fact, a lot of real life’s crummies are linked to the state of the environment. By one estimate, 24 percent of the global burden of disease can be attributed to environmental risk factors. For some specific diseases, that number is even higher—diarrhea owes 94 percent of its existence to the environment, lower respiratory infections owe 41 percent, and malaria, 42 percent.

If the existing environment has such a big impact, would it be possible to cultivate surroundings that would prevent some of these diseases? This is the question asked by a new study in Proceedings of the National Academy of Sciences, which looked at conservation efforts in the Brazilian Amazon rainforest, specifically in the context of those three conditions—diarrhea, acute respiratory infections, and malaria.

“The Brazilian Amazon is an appropriate setting to explore the health impacts of ecosystem changes because it has undergone both rapid land-use change, including conversion of nearly a fifth of the original forest cover to other land uses, and significant conservation efforts, including establishment of [protected areas] covering 44 percent of the region,” the study reads.

The researchers found that land-use policies are linked to noticeable health outcomes. The building of roads is associated with lowered acute respiratory infections and diarrhea—likely because of the access to healthcare they provide—but increases in malaria. Deforestation leaves more places for mosquitoes to breed, which could explain why roads are linked to more malaria.

When it came to protected areas, the study found that the type mattered. Strict protected areas like national parks were associated with reductions in all three conditions, “probably because … they effectively discourage interaction between forest and susceptible people,” the researchers write. “Sustainable-use” protected areas, which allow people to live there and sustainably harvest natural resources, “may increase malaria” because people who live and work there are more exposed to mosquitoes.

Other research has shown the health benefits of nature. Trees removed 17 tonnes of pollution from the air in 2010, saving 850 lives, as my colleague James Hamblin wrote. And living close to nature has been shown to reduce stress and boost memory. But this study moves the science forward by showing a fairly direct link between conservation efforts and better health. What’s good for the trees is often good for people as well. The Lorax would be pleased.

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