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Maple syrup production declines following masting
Joshua Rapp and Elizabeth Crone
Department of Biology
Flowering and seed production are energetically costly, which is hypothesized to play a role in driving masting dynamics. For spring-flowering species, energy is drawn from non-structural carbohydrate (NSC) stored in woody tissues. We hypothesized these same NSC stores provide the sugar in xylem sap that is tapped to produce maple syrup, and that maple syrup yields and seed production should be coupled. Specifically, we expected that in sugar maple, a masting species: 1) carbohydrate stores as measured by soluble sugars in xylem sap would be depleted after masting; and 2) seed production would increase after a resource threshold is reached. We tested these predictions at the landscape scale using monitoring data on seed production from the North American Maple Project provided by the Vermont Monitoring Cooperative, and maple syrup production from the United States Department of Agriculture National Agricultural Statistics Service. Maple syrup production data, detrended to remove a decade-long increase in syrup production reflecting greater harvesting effort, declined in the year following a mast year, demonstrating a cost of reproduction to trees, and maple syrup producers. We also found evidence for a resource threshold beyond which trees attempt reproduction, and a positive relationship between seed and syrup production in the same year. In addition, even though weather during the sugaring season is a strong predictor of sap flow, seed production was a stronger predictor of maple syrup production than climate alone, although a model containing both seed production and climate best predicted syrup production. Our results show that reproduction-driven internal resource dynamics of trees can have impacts on economic activity, and the importance of long-term monitoring data for testing ecological theory.