Dendrochronological reconstruction of forest tent caterpillar outbreaks in time and space, western Manitoba, Canada

Abstract

A tree-ring reconstruction of forest tent caterpillar ( Malacosoma disstria Hubner) outbreaks was conducted in the Duck Mountain Provincial Forest. Trembling aspen ( Populus tremuloides Michx.), balsam poplar ( Populus balsamifera L.), and paper birch ( Betula papyrifera Marsh.) tree-ring chronologies were used to identify periods of outbreaks from approximately 1800 to 2002. The impacts of the major forest tent caterpillar outbreaks of the 20th century were compared among four stand types and two age classes. The presence of white rings and growth suppression were used to identify three important outbreak periods, 1939–1948, 1961–1965, and 1982–1985, with another large-scale outbreak suspected during the 1870s. A roughly 20-year interval was observed between major outbreaks. Few differences were found between stand types, except during the 1960s, when mixed stands with jack pine ( Pinus banksiana Lamb.) registered more growth suppression and white rings. In general, the outbreak signal in the younger sites was variable. The importance of utilizing white rings and growth suppression data together is discussed. The major outbreaks of the 20th century generally started in the north of the Duck Mountain Provincial Forest. The technique was successful at identifying forest tent caterpillar outbreaks during the 20th and late 19th centuries, when no historical surveys were available.