Red spruce reviving in New England, but why?

In the 1970s, red spruce was the forest equivalent of a canary in the coal mine, signaling that acid rain was damaging forests and that some species, especially red spruce, were particularly sensitive to this human induced damage. Now, scientists are finding that red spruce are growing at levels almost two times the average for the last 100 years, a growth rate never before achieved by the trees examined.

Fuente : http://www.eurekalert.org/pub_releases/2013-08/ufs…