【英语时差8,16】森林燃料的可持续发展（在线收听）

Ya?l: Time to go again to the A Moment of Science mailbag. A listener writes: Dear Don and Ya?l, I know that eventually oil will run out and that we'll need to develop alternative sources of energy. And I keep hearing about things like wind and solar power and hydrogen fuel cells. But which of these seems most likely to emerge as a major source of energy in the future? Don: Good question. Of course, wind and solar power will most likely play roles, as well as nuclear power. But there's another potential source of renewable energy that you don't hear as much about--forests. Y: Wait, you mean like chopping down trees and using wood as fuel? D: Sort of. Y: But won't that lead to deforestation? That's what happened a few hundred years ago, before coal, when wood was the main source of energy and we cut down entire forests. D: True, but that's not what I'm talking about. Some energy scientists today see forests as sources of renewable energy. For example, forest biomass, meaning leaves and stems and small trees and other plants, can be used to make ethanol. Forest biomass can also be used to produce charcoal-like pellets that can be burned for energy. Y: OK, but we're still talking about cutting down trees, right? D: Yes, but not all the trees at once. And forest scientists know that cutting out smaller trees and plants is actually good for forests. When forests become too crowded with trees competing for light and water, biodiversity tends to suffer. So careful thinning out of forests can be healthy. Y: Interesting. So maybe one day we'll be running on forest power. D: Maybe.