Climate change is affecting the benefits society derives from forests. One such forest ecosystem service is maple syrup, which is primarily derived from Acer saccharum (sugar maple), currently an abundant and widespread tree species in eastern North America. Two climate sensitive components of sap affect syrup production: sugar content and sap flow. The sugar in maple sap derives from carbohydrate stores influenced by prior year growing season conditions. Sap flow is tied to freeze/thaw cycles during early spring. Predicting climate effects on syrup production thus requires integrating observations across scales and biological processes. We observed sap at 6 sugar maple stands spanning sugar maple’s latitudinal range over 2–6 years to predict the role of climate variation on sugar content and sap flow. We found that the timing of sap collection advanced by 4.3 days for every 1 °C increase in March mean temperature, sap volume peaked at a January-May mean temperature of 1 °C, and sap sugar content declined by 0.1 °Brix for every 1 °C increase in previous May-October mean temperature. Using these empirical relationships, we projected that the sap collection season midpoint will be 1 month earlier and sap sugar content will decline by 0.7 °Brix across sugar maple’s range by the year 2100 in an RCP 8.5 climate change scenario. The region of maximum sap flow is expected to shift northward by 400 km, from near the 43rd parallel to the 48th parallel by 2100. Our findings suggest climate change will have profound effects on syrup yield across most of sugar maple’s range; drastic shifts in the timing of the tapping season accompanied by flat to moderate increases in syrup yield per tap in Canada contrast with declines in syrup yield and higher frequencies of poor syrup production years across most of the U.S. range.
Graphical abstract
We used data on a forest-based ecosystem service, sugar maple (Acer saccharum) sap, spanning sugar maple’s latitudinal range to predict the role of climate variation on two aspects of sap productivity: sugar content and sap flow. The sugar in maple sap is derived from carbohydrate stores influenced by growing season conditions in the prior year, while sap flow is tied to freeze/thaw cycles during early spring. Our findings suggest optimal regions for sap production will move northward, with lower average production across nearly the entire range except for the far north, and provide spatially-explicit projections for forest managers and syrup producers making decisions on the location and viability of management for maple syrup production.
