The “sweet spot” for maple syrup production proposed by is not that sweet

Abstract

In their paper recently published in FEM (“Finding the sweet spot: Shifting climate optima for maple syrup production in North America”), Rapp et al. (2019) suggest that there is a marked “sweet spot” for maple syrup production (i.e., a climatic optimum associated with much higher yield) centered around the 43rd parallel. They also project that this climatic optimum could move 400 km northward in the future, as climate change drives temperatures to increase. As a result of this shift, they also predict that maple syrup production in the northeastern United States will rapidly decline in the next decades, and that the whole maple syrup industry could be at risk in several states. At the same time, they predict that maple syrup production will markedly increase in southeastern Canada, especially in the province of Quebec. Here we show that the predictive model built and used by Rapp et al. (2019) to project future maple syrup yield from climate scenarios is biased and presents several major flaws. We then demonstrate, using a data set of historical data many orders of magnitude larger than the one used by Rapp et al. (2019), that maple syrup yield is remarkably stable across a broad latitudinal and temperature gradient and therefore, that no climate optimum exists. This exercise leads us to conclude that the collapse of the U.S. maple syrup industry predicted by Rapp et al. (2019) is not based on solid evidence.