Lands that shelter forests have value often readily tallied by developers, but until now it’s been more difficult to prove the success of protecting those forested lands in pursuit of sustainability. That can put conservationists on the defense. Scientists have focused on what makes a protected area the most effective at preventing deforestation. Preserving forests means more trees to suck up greenhouse gasses, as well as prevent erosion, mitigate flooding, purify water and quell sandstorms.