Assessing the effects of resource extraction and climate-related disturbances on the growth of Picea mariana (Mill.) BSP (Pinaceae) in boreal peatlands in the Hudson Bay Lowland, Canada

The peatland-dominated Hudson Bay Lowland (HBL) is facing increasing pressures from climate change and resource extraction operations. Despite the potential for widespread changes in water availability to occur, information about hydrological and ecological feedbacks in the HBL remains limited. This study, located near the De Beers Victor diamond mine similar to 90 km west of Attawapiskat (Ontario, Canada), investigates the influence of mine dewatering activities ('pumping') and climatic variability on the radial growth of black spruce (Picea mariana (Mill.) B.S.P.) trees. Tree stem disks were collected from stunted black spruce trees in one reference (n=25) and three mine-affected bogs within the area of dewatering influence (n=41) along a transect of variable underlying aquitard (marine sediment) thickness. Pumping was not found to have influenced annual ring-width indices (RWIs) in mine-affected areas with either thick (6 to >18 m) or thin (< 5m) underlying marine sediment, as these sites showed similar growth patterns to the reference site during the period of mine operation. Analyses of the influence of climate on tree radial growth (1970-2018) using 20-year moving windows showed significant (p < 0.05) positive correlations (Pearson R) between residual RWI and mean monthly air temperature, including June (1979-2007 excluding the window of 1986-2006), August (1989-2018) and September (1984-2009). In addition, for the period during which ground temperature data were available (2011-2018), significant negative correlations were detected between residual RWI and mean monthly soil temperatures in late winter and early spring. The above relationships highlight the importance of both growing and shoulder season conditions for tree growth. As the HBL continues to respond to climate change, the growth response and potential proliferation of black spruce will undoubtedly influence the water balance and hydrological function of bog peatlands in the region.