Dendrochronological analysis of the response of tamarack (Larix laricina) to climate and larch sawfly (Pristiphora erichsonii) infestations in central Saskatchewan

The potential for deriving long records of climate and larch sawfly (Pristiphora erichsonii) infestation for central Canada from tamarack (Larix laricina) ring-width series was investigated. Analysis was based on a 314-year chronology developed from tamarack at a wetland site in Prince Albert National Park, Saskatchewan. The tamarack chronology was compared with a non-host 240-year black spruce (Picea mariana) chronology derived from trees at the same site and with historical records of sawfly infestation in the Prairie provinces. The two chronologies are similar to the late 1800s, after which there appears to be a decoupling. The existence of five major growth suppression events in larch (three preceded by light rings) from ~1880, compared with only two minor growth anomalies in the tree ring record prior to this time (1757-1880), may indicate either i) that tamarack has been relatively recently affected by the introduction of larch sawfly into the region in the late 1800s or ii) that 20th century outbreaks of larch sawfly have been more virulent, perhaps due to increasing temperatures and moisture stress. Climate-growth analysis indicates that larch trees at this location are sensitive to moisture, with low precipitation limiting annual growth. Possibly, increased moisture stress has also made larch more susceptible to the effects of defoliation. Because multiple signals coexist in the tamarack chronology over the 20th century, and there is a high frequency of missing rings, quantitative precipitation reconstruction using trees from this region presents difficulties.