MICHEL MARTIN, HOST:
Remember acid rain? In the 1970s and '80s, scientists found that rain 100 times more acidic than normal was harming the mountain forests of New England. The pollution was linked to fossil fuel plants in the Midwest. Now, a new study shows red spruce trees are recovering after decades of damage. From the New England News Collaborative, John Dillon has this report.
JOHN DILLON, BYLINE: On a steep slope in the Green Mountains of Vt., forest researcher Alexandra Kosiba does a kind of medical exam on a red spruce tree. Kosiba - everyone calls her Ali - uses a long drill-like instrument to extract a narrow slice of tree all the way into the core.
ALEXANDRA KOSIBA: This is the sound it makes. This is friction with the - pushing through because it's basically cutting the wood as it goes through. Moment of truth.
DILLON: This sample backs up what Kosiba and her colleagues observed in a recent study of red spruce in five northeastern states. After decades of decline, the trees are healthy again.
KOSIBA: It looks like the recent growth is quite large. And if you go back a decade, they start getting a lot smaller, and even another decade, they're really tiny.
DILLON: Indeed, three decades ago the news was much more grim. Millions of trees like this one were dying - their needles red and their growth stunted. The reason was acid rain. It's caused when pollutants released by fossil fuel plants downwind New England - chemically combine with precipitation and leach calcium out of the soil. The calcium depletion doesn't directly kill the tree, but makes them susceptible to stress and injury from cold winters. As recently as 2003, a deep freeze injured red spruce trees around New England.
PAUL SCHABERG: Sixty-five percent or more of the current-year foliage died that year.
DILLON: Paul Schaberg is a U.S. Forest Service scientist who has studied the spruce decline. He says that images of dead and dying red spruce forests in New England helped build the case for the 1990 Clean Air Act. That law, signed by the first President Bush, limited emissions of sulfur dioxide and nitrogen dioxide, the precursors of acid rain. Today, the recovery is impressive.
SCHABERG: It's real. It's recent. And it's broad-scale.
DILLON: Schaberg worked with Ali Kosiba on a recent study and has studied acid rain and forest decline for decades.
SCHABERG: It's a great scientific arc of monitoring, doing scientific research, informing policy, monitoring some more. And with some great surprises, like Ali's work showing this rebound in this species that was, you know, the epitome of an impact.
DILLON: Gene Likens first documented acid rain in the 1960s in a New Hampshire research forest. Now in his 80s, Likens says the rain, snow and mist is 80 percent less acidic at that forest than at its highest levels 50 years ago. He says those early studies provided the groundwork for the 1990 Clean Air Act.
GENE LIKENS: And that's what science does - we ask questions and look for answers to those questions, and then I'll try to communicate that information to decision makers in hopes that actions can be taken.
DILLON: While the red spruce recovery is good news, other species like sugar maples growing on calcium-poor sites are still threatened. And part of the reason the red spruce are doing better is warmer winters due to climate change, but researchers say that northern forests will likely suffer in the long run as the region continues to heat up. For NPR News, I'm John Dillon. Transcript provided by NPR, Copyright NPR.