Changing climatic sensitivities of two spruce species across a moisture gradient in Northeastern Canada

This paper examines the variability in the relationship between climate and radial growth of black spruce (Picea mariana (Mill.) B.S.P.) and white spruce (Picea glauca (Moench) Voss) trees across central Labrador, Eastern Canada. Using climate-sensitive trees, an 11-year running Pearson correlation is applied to local records to examine the relationship between radial tree growth and climate over the last 50 years and the spatial pattern in this relationship with increasing distance inland from the Labrador Sea. Results indicate that there is a high degree of instability in the climate/tree-ring sensitivity despite an overall statistically significant relationship throughout the instrumental time period (1942 to present). Although some periods of reduced climate sensitivity are coincident with insect outbreaks, others cannot be explained by forest disturbance factors. Spatially, the two sites that are most representative of higher elevation areas have more time-stable climate-growth relationships than those inland or along the coast. The results also suggest that the stability of the relationship may be the result of moisture availability, rapid changes in precipitation and temperature, and site-specificity.