Radial growth analysis of Larix laricina from the Lake Duparquet area, Quebec, in relation to climate and larch sawfly outbreaks

A dendrochronological study was performed at sis sites dominated by eastern larch, Larix laricina in Ouebec's southwestern boreal forest. The objectiv es were to reconstruct periods of larch sawfly (Pristiphora erichsonii) out break in the region and to determine which physical factors (precipitation, temperature, water level or drought) explained the greatest variation in r adial growth. From the presence of light latewood rings followed by periods of growth suppression. we identified larch sawfly outbreaks for the years 1895-1912, 1937-1942, and 1955-1962. We suspect that additional outbreaks o ccurred in the early 1920s, late 1970s and early 1980s as well, but at the same time as spruce budworm outbreaks (Choristoneura fumiferana). Response function analysis demonstrated negative relationships between larch radial growth and May and August precipitation and May and September current year water level, and demonstrated positive relationships with May current year drought index and September previous year drought index. These results sugg est that flooding in the early growing season and excessive water levels at the end of the growing season may negatively affect larch radial growth. O ur results also indicate an increase in the year-to-year variation in radia l growth in larch sites subjected to flooding. This may reflect the increas e in the Lake Duparquet water level at spring break up.