The fate of the world’s forests on a warming planet has long been one of the great unanswered questions about climate change. Now, new research is complicating the picture further, suggesting that big shifts are already under way in how forests work.

A paper published Wednesday suggests that trees in at least some parts of the world are having to pull less water out of the ground to achieve a given amount of growth. Some scientists say they believe that this may be a direct response to the rising level of carbon dioxide in the air from human emissions, though that has not yet been proved.

If the research holds up, it suggests some potential benefits for forests. They might be able to make do with less water, for instance, becoming more resilient in the face of drought and higher temperatures as climate change proceeds.

But the new finding also has potential downsides, scientists said. The immense volume of water that trees pull out of the ground winds up in the atmosphere, helping supply moisture to farming areas downwind of forests. So if trees use less water, that could ultimately mean less rain for thirsty crops in at least some regions of the world.