Maple syrup production declines following masting

Maple syrup is a non-timber forest resource, for which yield depends strongly on natural processes. Past research has heavily emphasized the role of weather and climate in determining sap flow, and the relationship between sap flow and syrup yield. However, syrup yield depends on sap sugar content, as well as sap flow. Although sap sugar content varies widely among years, less is known about the causes of this variation. Drawing on ecological theories for causes of mast-seeding in trees, we hypothesized that a trees' carbohydrate stores would fluctuate through time in concert with seed production, and that this fluctuation would affect sap sugar and syrup yield. We evaluated weather variables and past seed production as possible causes of inter-annual variation in maple syrup yield in Vermont, USA. Past seed production was strongly correlated with current syrup yield, suggesting that carbohydrate costs of reproduction affect stores. Climate variables were also important for syrup yield, but were only statistically significant predictors after accounting for variation in seed production. Seed production occurs several months before syrup production, and can be used as a way to forecast expected syrup yields, and prepare harvest plans accordingly.