Insect in hemlock forests causes loss of canopy, gain of invasive plants

BERKELEY — Deep in the hemlock forests of the Eastern United States, a tiny, aphid-like insect may be playing a giant role in transforming an ecosystem, according to new research by ecologists at the University of California, Berkeley. The understory environment of hemlock forests, characterized by uniformly low light levels and little plant cover, has been significantly altered by the decline of the hemlock canopy caused by an exotic pest, the hemlock woolly adelgid. (Anne Eschtruth photo) It's been well-documented that the spread of the hemlock woolly adelgid, an exotic pest native to Asia and introduced to the Eastern United States in the 1950s, has led to a decline of the shade-providing canopy in forests of eastern hemlock trees. The insect ( Adelges tsugae ) sucks fluid from the base of hemlock needles, causing the needles to drop and the branches to die. The new study has found that this loss of canopy is also setting the stage for the successful invasion of non-native plants. The canopy decline leads to even greater invasion of non-native plants when combined with a high concentration of the plants' seeds and white-tailed deer in the affected area. "This study provides important information for the management of natural resources," said study co-author John Battles, UC Berkeley associate professor of ecosystem sciences.