Recent decline in sugar maple (Acer saccharum Marsh.) growth extends to the northern parts of its distribution range in eastern Canada

Sugar maple (Acer saccharum Marshall) growth in the species' southern range has been declining since the 1980s, putting at risk a variety of ecosystem services that the species provides. Heatwaves, drought, frosts, acidic deposition, and insect defoliation, all reducing photosynthetic activity, have been suggested to be behind the phenomenon. Because the geographic scope of previous studies on maple growth is limited to the southern temperate biome, it is not currently understood whether the same negative trends and factors affecting growth rates apply to the species in more northern regions of its distribution range. Here we used annual ring-width data of 1675 trees from a network of 21 sites in Quebec and Ontario between 45N and 48N to reconstruct maple growth and to analyze its trends and climatic drivers since 1950 CE. We developed a retrospective tree growth index by employing a Generalized Additive Mixed Model (GAMM) that accounted for tree age and size, terrain altitude, slope, competition and mean site climatology. Our reconstruction suggested considerable geographical variations in maple growth trends, with declining growth being less pronounced in the central portion of the study region. The growth decline persisted at the time of sampling in 2019 and 2020. Maple growth negatively correlated with the summer vapour pressure deficit (VPD) during both the previous and current growth seasons. As the decline in sugar maple growth is observed at the northern limit of its distribution, climate change may not favor the expansion of sugar maples to the north. The observed decline along with increasing VPD will likely have a negative impact on the ecosystem services supported by this species and calls for management adaptation measures.