Compositional vegetation changes and increased red spruce abundance during the Little Ice Age in a sugar maple forest of north-eastern North America

Abstract

In north-eastern North America, the recent red spruce decline has been linked to atmospheric pollution, notably acid rain, although climate was also advocated as a potential factor. A high resolution lake sediment pollen stratigraphy was obtained to elucidate long-term trends in tree-species abundance in a sugar maple—yellow birch forest. The reconstructed history (~250–1996 A.D.) showed a steady increase of red spruce after 1300 A.D., with a peak between 1600 and 1900 A.D. followed by a strong decline in the last century, while sugar maple and yellow birch experienced an opposite trend. Red spruce abundance reached its apogee during the cool Little Ice Age (LIA) and decreased abruptly when annual temperature in the region increased by 2 °C in the last 125 years. American Beech was much more abundant in the forest before the LIA, typifying a sugar maple—American beech forest as the dominant forest type during the Late Holocene. Our results suggest that climate warming has played an important role in the current red spruce decline, the latter having been initiated well before acidic depositions reached deleterious potential effects on red spruce. Climate warming probably acted as a long-term predisposing factor that was aggravated by atmospheric pollution, in the last decades.