Forecasting maple sugaring yields in changing climate

Background/Question/Methods

Maple sugaring depends on healthy and mature maple groves and is intimately linked to weather, as sap water extraction requires freeze-thaw cycles. In a warming world, the rapidly expanding maple sugaring industry in North America is thought to be threatened, because winter temperatures are projected to increase disproportionately in eastern North America. Previous studies agreed that the region of maximum sap extraction will shift northward, as warm winters limit production at the southern margin and cold growing seasons prevent the establishment and production at the northern margin. However, the climate impacts on maple sugar production between these range margins remains highly debated. Some authors estimated small declines or no net changes, while others projected large increases in maple sugar yields. To reduce the uncertainty in projections of future maple sugaring yields, we combined production data for more than 10 000 producers from 648 municipalities in Québec over 15 years (2005-2021) with meteorological data of the previous growing season, the previous winter, and the sugaring season. We regressed maple sugar yields on a selection of biologically-meaningful meteorological variables (e.g., number of freeze-thaw cycles during the sugaring season and minimum winter temperature) to better constrain the climate-sensitivity of maple sugar yields.

Results/Conclusions

We find that maple sugar yield is primarily dependent on the length of the sugaring season with secondary influences of previous winter and growing season temperatures. Across eastern North America, our model confirms an advance of the ideal sugaring season by more than two weeks by the end of the century. Although we do not forecast a significant change in the mean length of the tapping season, increased year-to-year variation in the sugaring season length may lead more often to exceptionally short seasons, hence low maple sugar yields. Our projections also indicate a general decline in maple sugar yields due to reduced sap sugar concentrations in a warming climate, but the net effects are dependent on the exact location and anticipated climate. The improved projections presented here are a valuable tool to guide the adaptation of maple sugaring operations to a warming climate and can assist in identifying suitable locations for the continued expansion of maple sugaring activities. With the projected increases in demand and the subsequently anticipated expansion of the sector, sustainably managing the maple groves becomes increasingly important and tools, like the model developed here, will be crucial to balance ecological and economic function.