Forest declines: is mighty moss to blame?

Forest declines: Is mighty moss to blame?

Something has been killing forests across industrial Europe and the northeastern United States. Though acid rain and ozone have been the primary suspects, research by University of Colorado geographer Lee Klinger now suggests that the actual assassin is probably a cool, springy carpet of moss.

Klinger, who works at the university's Institute for Arctic and Alpine Research in Boulder, began his studies in arctic Alaska, where mosses are the dominant plants. Later, when he turned his attention to why forests were dying -- there and elsewhere -- he assuemd he'd be tracking a deadly pollutant. Instead, he found himself on the trail of mosses. To date he has looked at 100 regions in some 30 states experiencing forest dieback. "And I have not yet found one," he says, "that does not fit the pattern" -- dead, very fine "feeder" roots directly underlying a carpet of mosses. He has observed that even a few inches outside the edge of the moss, tree roots are healthy.

Calling mosses "terrestrial sponges," Klinger says they can hold enough water to "saturate the surface soils right beneath them, making that zone anaerobic (free of oxygen)." As feeder roots -- the ones that take in nutrients but have the smallest oxygen storage -- grow into that zone, they die. But additional factors may play important roles. For example, Klinger says mosses can kill mycorrhiza -- symbiotic fungi that help tree roots absorb nutrients. Moreover, mosses acidify water passing through them. Once the water reaches a critical acidity, toxic aluminum in the soil becomes soluble and available to the tree, says Klinger.

This acidification, Klinger says, explains why his work does not exonerate acid rain's role in forest declines. Since mosses love acidic conditions, acid rain may actually foster moss growth, accelerating this natural process of forest death.