Effects of Rising Temperatures On Sugar Maple Tree Sap Production For The Maple Syrup Industry

Background

Diving into the topic of global climate change requires an understanding of the publications from the Intergovernmental Panel on Climate Change, which provides a comprehensive report from several participants and studies. This report consolidates findings on how climate change can affect the entire planet. One detail that cannot be disputed is that over the last few decades, ecosystems have experienced alterations related to a rapidly changing environment. A few of the changes, as reported by the IPCC 2014 synthesis report are continued warming, increased variability of surface temperatures annually, and changes to precipitation patterns (4).

Figure 2: Shows the direct relationship between CO2 emission increase and rising temperature from 1880-2017. This trend is expected to continue to grow in the future

The tradition of producing maple syrup from the sap of maple trees is something that has long been a practice in the northern forests of North America. Maple syrup is held particularly close to the heart of the people of New England in the United States. While there are several maple tree species, Acer saccharum is most commonly used for maple syrup production due to higher sugar content in the sap (2).

It is crucial to examine how this particular species may respond to a changing environment in order to make informed predictions on production and management. The maple syrup industry is vastly prevalent across the Northeastern U.S. and into Québec Canada. Changes to how these trees operate can have repercussions on the forests in these areas for ecosystem sustainability, management of these forests, and for economical preparation. The sugar maple tree is important for many reasons; including that it is a significant source of income for harvesters, tapping is viewed as a traditional symbol of identity (see figure 4), and these trees are the backbone of foliage coloration distinctly marking the fall season in New England. (7).

Figure 4: showing on of the many ecosystem services provided by the sugar maple tree: Maple Syrup production as a provisional service. https://www.thoughtco.com/maple-sap-and-syrup-production-1342654

Past data trends will help us to recognize the response and adaptations of these trees as they have already happened to allow better predictions for how the trees will continue to respond and adapt in the coming years. Fifty years ago, NY and New England accounted for 80% of international maple syrup production, with the remaining 20% being attributed to production in Canada (6). There has already been a documented Northward shift from the previously described range of sugar maple trees. It is important to understand this range shift in order to predict and prepare for another range shift and production management in the coming century (Figure 5 predictions). Canada has become the largest producer of maple syrup, accounting for 70-75% of the world’s maple syrup production (5), with the flag of the nation featuring a large maple leaf and the majority or maple syrup produced in Québec. The majority of U.S. production occurs primarily in New England, specifically in Vermont.

Figure 5: the historical range of the sugar maple range in 1950-1999 next to an image of the projected range for the end on the century 2090-2099 (10).

Maple Industry in the United States and Canada

Uses

These trees are not just the primary producer of maple syrup. There are many other uses associated with the sugar maple. They are valuable timber used for flooring and furniture, seeing as every NBA franchise has a court made out of Sugar Maple flooring. The timber is also used to make bowling pins, musical instruments, and baseball bats (1). These trees are also a habitat and source of food for the ecosystems they exist in. Several species of squirrels feed off the seeds, buds, twigs and leaves from the sugar maple. Squirrels and nesting songbird use the hollows in the trunks for shelter. Moose, white-tailed deer and snowshoe hares forage the leaves and twigs. The foliage provides homes to many species of insects (1).

Figure 6: Spout placed into the trunk of a maple tree with a collection bucket fixed below for the sap flow collection process. https://www.farmandfleet.com/blog/how-to-tap-maple-trees/

Value

Studies have shown that North American maple syrup production provides economic value from the provisional sources provided by the trees in sap flow to generate maple syrup. This value can be commercially scaled or traditionally traced to individual farmers. In the U.S., nearly 4.2 million gallons of maple syrup were produced in 2018, which resulted in an estimated value of 142 million USD, according to the U.S. Department of Agriculture (8). Comparatively, Canada reports on Statistics Canada show a production of 13.2 million gallons of maple syrup produced in 2019 to generate a value of 517 million dollars. This is an astronomical amount when you consider that is generally takes 40-50 gallons of the maple sap to produce 1 gallon of maple syrup (40 sap: 1 syrup), depending on the °Brix. Typically, 2.2 °Brix is required from 43 gallons of maple sap to produce 1 gallon of maple syrup (3). That is A LOT of sap!

Figure 7: Maple syrup produced in Canada. This shows the different coloration of the maple syrup that is used to distinguish between “grade” or syrup. https://ccsearch.creativecommons.org/photos/4e2e0430-c796-4495-8f84-3f8cb728fec3

Characteristic differences between the two nations

Utilizing studies of North American maple syrup production compared to production in Canada allows us to see the economic impacts in each country. In the U.S., nearly 4.2 mil gallons of maple syrup were produced in 2018, resulting in an estimate value of 142 million dollars according to the U.S. dept. of Agriculture (8). Canada reports 13.2 mil gallons of maple syrup production in 2019 with an estimated value of 517 million dollars according to the website Statistics Canada (https ://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=3210035401).The key differences between the maple syrup in these two countries is that U.S. is primarily a collection of thousands of private sugar-makers with no central authority, whereas Canadian syrup is dominated by the Québec Federation of Maple Syrup Producers that play a role in primarily bulk distribution of maple syrup (12). The only significant difference in the syrup produced would be in relation to sap sucrose content before syrup production and the system for labeling quality.

Figure 8: maple syrup farm in New England U.S. fixing buckets to trees in preparation of the upcoming tapping season. https://civileats.com/2019/04/03/could-maple-syrup-be-a-climate-change-solution/

How does temperature directly affect the sugar maple tree (biology)

Ideal temp

The ideal temperatures for sap sucrose content would be that the cooler average growing season temperatures (May-Oct) produces higher sap sucrose content. If the temperatures are warmer the lower the °Brix and thus the less quality the sap. Less quality sap requires more in gallons to produce a single gallon of the familiar maple syrup (10). The sap sucrose content decreases by 0.1°Bx for every 1°C rise in average temperature for the previous growing season (10). This negative linear relationship can be seen in figure 9, where we observe more northern locations having lower mean growing season temperatures, produce sap with higher sap sucrose content. Another ideal temperature factor is the interannual temperature changes during the tapping season. Air temperatures required for tapping are below 0°C at night and just above freezing during the day to produce the proper internal pressure that is essential to tap the sap (6).

Other factors?

Figure 9: Graph depicting the current negative linear relationship between the previous growing season mean temperature and sap sugar content (10).

There are several other factors that come into play when discussing the health of the maple syrup industry. Including precipitation, atmospheric CO2, invasive species, as well as temperature.

Figure 10: Image showing industrial productions’ negative effects on releasing burning fossil fuels and greenhouse gasses into the environment. https://www.raconteur.net/technology/industrial-iot-climate-change

Atmospheric carbon increase is an indirect factor that affects the sugar maple tree because it is coupled with rising temperatures. The interannual warming that goes along with CO2 increase would mean the frost season is diminishing leading to less optimal sap tapping temperatures and short season for decreased maple syrup production. Another factor is that increased CO2 emission equates to a less than optimal habitat, fewer trees, and decreased maple syrup production.

Increased acid rain occurrence would also affect the industry as more CO2 and other elements will pervade the rain falling onto ecosystems that can be detrimentally impacted. Acid rain has a strong negative effect on nutrient cycling. The calcium (Ca) content of soil helps to maintain tree health is crucial to carbon metabolism and stress response. Acid rain has been shown to lead to a decline in maple trees because of Ca loss (11). A decline in population means there are less healthy trees to tap and thus less maple syrup production

Figure 7: Diagram showing the believed mechanism of how Ca loss in the soil, a proposed result of increased acid rain, would lead to loss/decline of sugar maple trees (9).

Conclusion

Maple syrup is a massive industry in the U.S. and Canada, and it generates millions of dollars in revenue. With a changing climate, it is vital to see how those changes might impact something of such high economic value and cultural importance. Due to how dynamic climate change is, we must be prepared for the possibility that we are not able to change things overnight, but rather be prepared to deal with the immediate challenges and try to initiate change now for the future. Reduction of CO2 emission and burning of fossil fuels that lead to added atmospheric concentrations is an essential and necessary step. Reducing the acidity of precipitation will require a global effort but will have profound impacts on a number of ecosystems, not just for sugar maples and the maple syrup industry. Continuation of data presentation will allow governments, policy makers, citizens, and farmers to be more cognizant of the changes to the industry and how to mitigate those changes so we may see the maple syrup industry continue to thrive in the U.S. and Canada.

Future directions include quantifying analysis of how each factor separately influences the maple industry as well as a combination of factors may be additive or reductive. Taking a look at how individual stands may be impacted gives more refined ways to help manage and maintain the maple syrup industry.

Citations

(1) Beals, Whit. "Meet the Sugar Maple | New England Forestry Foundation". New England Forestry Foundation, 2018, https://newenglandforestry.org/2018/10/02/meet-the-sugar-maple/.

(2) Doner, L.W. "SUGAR | Palms and Maples". Encyclopedia of Food Sciences And Nutrition, 2003, pp. 5657-5659. Elsevier, doi:10.1016/b0-12-227055-x/01162-7. Accessed 17 Apr 2020.

(3) Heiligmann, Randall Bruce et al. North American Maple Syrup Producers Manual. Ohio State University Extension, 2006.

(4) IPCC, 2014. Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change In. [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)], Geneva, Switzerland, p. 151.

(5) Matthews, Stephen N., and Louis R. Iverson. "Managing for Delicious Ecosystem Service Under Climate Change: Can United States Sugar Maple (Acer Saccharum) Syrup Production Be Maintained in A Warming Climate?". International Journal of Biodiversity Science, Ecosystem Services & Management, vol 13, no. 2, 2017, pp. 40-52. Informa UK Limited, doi:10.1080/21513732.2017.1285815.

(6) Maclver DC, Karsh M, Comer N, Klaassen J, Auld H, Fenech A (2006) Atmospheric influences on the sugar maple industry of North America. Environment Canada, Adaptation and Impacts Research Division, Occasional Paper 7

(7) Murphy, B.L., A.R. Chretien, L.J. BrownNon-timber forest products, maple syrup and climate change J. Rural Commun. Dev., 7 (2012), pp. 42-64

(8) NASS, USDA. "United States Maple Syrup Production". Nass.Usda.Gov, 2018, https://www.nass.usda.gov/Statistics_by_State/New_England_includes/Publications/Current_News_Release/2018/Maple%20Syrup%202018.pdf. Accessed 20 Apr 2020.

(9) Pye, John M et al. Advances in Threat Assessment and Their Application To Forest And Rangeland Management. U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, 2010.

(10) Rapp, Joshua M. et al. "Finding The Sweet Spot: Shifting Optimal Climate For Maple Syrup Production In North America". Forest Ecology and Management, vol 448, 2019, pp. 187-197. Elsevier BV, doi:10.1016/j.foreco.2019.05.045.

(11) Schaberg, Paul. "Acid Rain and Sugar Maple Decline". Fs.Usda.Gov, 2017, https://www.fs.usda.gov/treesearch/pubs/54127.

(12) Trubek, Amy. "Maple Syrup: Differences between Vermont and Quebec." Cuizine, volume 2, number 2, 2010. https://doi.org/10.7202/044354ar