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. In the course of studying the lingering effects of acid rain and whether trees stored less carbon as a result of winter injury, U.S. Forest Service and University of Vermont scientists came up with a surprising result -- three decades later, the canary is feeling much better. Decline in red spruce has been attributed to damage that trees sustain in winter, when foliage predisposed to injury by exposure to acid rain experiences freezing injury and dies. Paul Schaberg, a research plant physiologist with the U.S. Forest Service's Northern Research Station in Burlington, Vt., and partners studied red spruce trees in Vermont, New Hampshire and Massachusetts. They found that the influence of a single damaging winter injury event in 2003 continued to slow tree growth in New England for 3 years, longer than had been expected, and had a significant impact on carbon storage.
They also found something they did not expect.
"The shocking thing is that these trees are doing remarkably well now," said Schaberg, a co-author on the study. Researchers found that diameter growth is now the highest ever recorded for red spruce, indicating that it is now growing at levels almost two times the average for the last 100 years, a growth rate never before achieved by the trees examined. "It raises the question 'why?'" Schaberg said.