Planting trees may not be as obviously green as you think – at least that’s what scientists at Duke University found. Tree-planting is generally viewed as a no-brainer antidote to climate change, because growing trees soak up carbon dioxide, a greenhouse gas, from the air.

But trees planted expressly to help remove CO2 from the air tend to be fast-growing species (more growth, more CO2), and that means they also need more water. A team of researchers, who published their results in this week’s issue of the journal Science, surveyed 500 newly planted forests around the world and found that these tree plantations reduced the amount of water in nearby streams by half. In some cases, the streams dried up altogether. For a clearly written article about the paper, click here.

The results don’t mean that planting forests to help lower atmospheric carbon dioxide levels is necessarily a bad thing – just that with this, as with most solutions to environmental problems, there are trade-offs. Increasingly, solving one environmental problem may come with a cost to another part of the environment. (For instance, a massive dam currently under construction in Iceland will produce hydropower to run an aluminum smelter – which otherwise would be located elsewhere and powered by coal, adding polution and greenhouse gases to the atmosphere. But Iceland’s climate-friendly solution comes at a great cost to nature: the dam is being built in a fragile wilderness ecosystem that’s home to rare plants.)

Photo credit: EPA