Maple syrup production declines following masting Joshua Rapp and Elizabeth Crone Department of Biology Tufts University 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.

1. Maple syrup production declines
following masting
Joshua Rapp
Tufts University and Harvard Forest
rapp@fas.harvard.edu

2. Acknowledgements
Data and Support
People
Elizabeth
Crone
Dash
Donnelly
Casey
Mangnall
Natalie Kerr

4. Masting as a reproductive
strategy
Definition:
 Episodic and synchronous
production of seeds across a
population
Sugar maple seed fall in The
Bowl Natural Area, White
Mountain National Forest
Graber and Leak, 1992

5. Masting as a reproductive
strategy
Why not just make the same number
of seeds each year?
 Density-dependent benefits to
fitness
 Escape seed predators
 Attract seed dispersers
 Pollination efficiency

6. Masting as a reproductive
strategy
Proximate mechanisms variable
reproduction
 Resource Budget Model (RBM)

7. Reproductive litter fall
can equal or exceed
vegetative litter fall in
mast years

8. Reproductive litter fall
can equal or exceed
vegetative litter fall in
mast years
Flowering before leaves come
out requires stored resources
Non-structural carbohydrates:
energy reserves of a tree

9. Reproductive litter fall
can equal or exceed
vegetative litter fall in
mast years
Flowering before leaves come
out requires stored resources
Non-structural carbohydrates:
energy reserves of a tree

10. Resource Budget Model
6CO2 + 6H2O
light
C6H12O6 + 6O2

11. Resource Budget Model
6CO2 + 6H2O
light
C6H12O6 + 6O2

12. Resource Budget Model
6CO2 + 6H2O
light
C6H12O6 + 6O2

13. Resource Budget Model
6CO2 + 6H2O
light
C6H12O6 + 6O2

14. Resource Budget Model

15. Why Sugar
Maple?
• Bimodal seed
production
• Maple syrup
production as a
potential proxy of
carbohydrate stores
• Potential effect of
seed production on
maple syrup yield
2011
2012

16. Does masting affect syrup
production?

17. Resource Budget Model Predictions
1. Resource stores
(NSC) should be
high just before
flowering.
2. Masting should
deplete NSC

18. Sugar Maple Seed Production in Vermont

19. Maple syrup production in Vermont –
detrending the data

20. Masting and syrup production in Vermont

21. What about the weather?

22. What about the weather?

24. Relative importance (left, top) and shrinkage-adjusted
coefficients (left, bottom) from model averaging
analysis.
Adjusted R2 (below) best model including seed
production in the previous year only, weather only, or
both seeds and weather.

25. Summary – masting and maple
syrup
• Masting depletes sap sugar
and leads to lower maple
syrup yields
• Seed production is a better
predictor of syrup production
than weather during the
tapping season

26. The take
home…
 NSC =
 Theory informs
practice
 Importance of life
history in considering
climate change
effects on maple
syrup industry