The Impacts of Weather and Climate on Maple Syrup Production

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Published on:

January 13, 2022

Focus On A Maple Syrup Producer: Don and Jodi Gale From Lincoln, Vermont

Don Gale persevered through a challenging maple sugar harvest last season. A prolonged cold spell in February and March kept sap locked up in the trees until March 11 at his maple sugar operation in Lincoln, Vermont, which is around two weeks later than normal. When daytime temperatures finally exceeded freezing, the triggering factor that gets maple sap flowing, the region observed too much of a good thing, and the temperature soon exceeded 60 degrees Fahrenheit on three consecutive days.

This was too warm too fast, as sap cycles best through sugar maples when nighttime temperatures drop below freezing, followed by daytime temperatures in the upper 40s to mid-50s. Maximum temperatures in the 60s are beyond this range, and if they warm up so much that minimum temperatures stay above freezing, the flow stops. Another danger of 60-degree days is that such warmth can invite trees to bud, which turns the sap sour, rendering it useless for maple syrup production, and ending the sugar season.

Maple Syrup Producer: Don and Jodi Gale From Lincoln, Vermont.

Although Don’s harvest survived the sudden pulse of 60-degree weather, the sugar season ended on April 10, wrapping up with less than one month of productivity. This was noticeably shorter than the typical year, which experiences around six weeks of sweet-flowing sap.

Another challenge Don faced last season was an abnormally low sugar content in the sap. This can be expected in a sugar season following a dry growing season, and prolonged drought in Vermont the year before lowered the sugar content of sap around the state. Low sugar content means more sap is required to produce the same amount of maple syrup. Last year, 105,000 gallons of sap produced 1,500 gallons of syrup for Don, or 70 gallons of sap for one gallon of syrup.

Don and his wife Jodi have run Twin Maple Sugarworks since 1988, and over the years they have seen good and bad harvests. Last season was not the first short season or the first time the sap had a low sugar content. Don recalls one year when he put buckets out to collect sap on a Monday and the season came to an end by Friday of the same week.

Don does not use buckets anymore; his operation installs 5,200 taps in a sugarbush that is mostly comprised of sugar maples. His taps are connected to plastic tubes that are placed in lines down the mountain, using gravity as much as possible to increase the sap flow speed. His operation now uses a vacuum system, which creates low-pressure suction, serving to both increase the speed of the sap flow, while keeping the line and tap hole cleaner, with less bacteria.

The Impacts of Weather and Climate on Maple Syrup Production

Last year’s low-production season came directly on the heels of a blockbuster season the year before, when everything clicked perfectly. A prolonged stretch of sunny, dry weather and light winds blessed the hillsides of Vermont back then, as sub-freezing nights were followed by mild days, which produced a bountiful harvest of maple sap with high sugar content.


Environmental Factors That Impact Sugar Maple Growth

The sugar maple is Vermont’s most common tree species, according to Vermont’s Climate Assessment.The species is also very prolific in Upstate New York and the Canadian Province of Quebec. The climate is ideal for sugar maples in these regions, as are the nutrient-rich soils that support these trees.

Ali Kosiba, climate forester with the Vermont Agency ofNatural Resources, explains that sugar maples prefer deep, organic soil that is rich in nutrients, with elements such as calcium and magnesium, because the tree species has very high nutrient demands. Although the climatology of New Hampshire resembles Vermont, sugar maples are less common there because the soils are more granitic and less nutrient-rich.

Environmental Factors That Impact Sugar Maple Growth

The U.S. Forest Service’s Tree Atlas map for the current inventory of sugar maple trees depicts high importance values in Vermont and Upstate New York, as well as some areas in northern Pennsylvania and near the central and western Great Lakes. A sharp east-to-west line demarcates the extreme southern boundary for this species in Tennessee and Missouri, south of which weather conditions are too hot for sugar maples.

Sugar maples are sensitive to temperature, with sap volume responding to minimum air temperatures below freezing and maximum air temperatures generally exceeding around 46 degrees Fahrenheit (8 degrees Celsius). The graphic below depicts sap volume on a plot of maximum and minimum temperatures, with maximum volume produced when sub-freezing nights are followed by mild days.

Environmental Factors That Impact Sugar Maple Growth: Sugar maples are sensitive to temperature.

Don Gale explained to me that not only does temperature impact the quantity of sap flowing through trees, but it also affects the natural bacteria counts, which change the sap color and taste. Colder temperatures produce a lighter syrup with less bacteria, whereas warmer temperatures produce a darker syrup with more bacteria and a stronger flavor. He clarified that some people prefer the darker syrup, even though it has more bacteria in it.

They say a picture is worth a thousand words, and Don preserves an excellent visual, with dozens of syrup flasks stacked on a shelf that walk us through last season’s maple syrup product. The miniature bottles are arranged chronologically, telling the story of how syrup characteristics changed through the season. Don recounted with crystal-clear memory each cold spell and warm up that led to an immediate change in the characteristic of his syrup.

The flask shelf drove home for me Don’s point that maple syrup is highly sensitive to the weather.

The flask shelf drove home for me Don’s point that maple syrup is highly sensitive to the weather. The shelf contains 57 bottles telling the story of a sugar season that lasted only around 30 days. This works out to an average of nearly two bottles per day for the sugar season, which is remarkable, because numerous times we see the color change drastically from one bottle to the next. This means that sometimes the sap characteristics changed substantially within the same day.


Maple Syrup Provides An Important Role in Vermont's Economy

During my visit to Vermont, I learned about the important role of maple syrup in the state’s economy. This was visually evident, as I drove past countless stores that sell a wide variety of maple products, including syrup, candy, cream, and a favorite local maple ice cream called acreemee. These stores cater to a tourism base that comes to Vermont for “wholesome” activities, such as fall foliage tours and outdoor recreation.

Important role of maple syrup in the Vermont economy.
Vermont maple products, including syrup, candy, cream, and a favorite local maple ice cream called acreemee.

I could not escape encounters with maple syrup production even when I was not looking for it, like during an afternoon GeoTrek at MiltonTown Forest, a 485-acre recreation area with hiking trails in Westford, Vermont. On the back area of those trails, I ran into blue plastic tubes that connect trees to a main line for maple syrup extraction. As required by law, the taps had been removed from the trees, but the tube lines were permitted to remain in the forest.

Blue plastic tubes that connect trees to a main line for maple syrup extraction.

The robust maple syrup industry brought in $54 million in revenue for sugar makers in 2019. In addition to generating a profit for sugar makers, this sector creates jobs for distributors and sellers, as well as a fully-developed business sector that includes marketers and publicists.

I was able to interact with professionals from these sectors, as well as physical and social scientists, while participating in the Vermont Maple Conference, which fortunately fell during my visit to Vermont. The conference was hosted by the University of Vermont Extension and Vermont Maple Sugar Makers’ Association.

A growing concern for the maple sugar industry is the impact of climate change on the forest. Ali Kosiba provided an excellent talk at the conference that addressed this topic, titled, “Sugar Maple Health and Climate Change.” From Dr. Kosiba’s presentation and a follow-up conversation with her, as well as reading the recently released Vermont Climate Assessment and other academic materials, I was able to understand the major issues related to climate change and maple sugar production, which I present in the next section.


The Impact of Climate Change on Maple Sugar Production

Although most literature about the impacts of climate change on the environment, including forestry and the harvest of forest resources, focus on negative impacts, it is important to note that a few climate change factors are positive, leading to increased forest productivity. Longer growing seasons and increased carbon dioxide content in the atmosphere lead to more productivity because they provide a longer time for photosynthesis to take place. Increased atmospheric carbon dioxide levels are sometimes referred to as, “The Fertilization Effect,” as carbon dioxide is an important input that trees use to grow. According to the Vermont Climate Assessment,Vermont’s freeze-free period, one metric of the growing season, has increased by three weeks since 1960.

However, the Vermont Climate Assessment clarifies that these positive factors will be countered by several negative factors, including less ideal temperatures, drought and soil nutrient loss. This section addresses these factors in greater detail.

Vermont’s annual average temperature has increased by more than 2 degrees Fahrenheit since the year 1900, changing from a mean temperature of nearly 40 degrees to approximately 43 degrees Fahrenheit. This temperature increase moves the timing of sap collection earlier during the sugar season and found that an increase of 1.8 degrees Fahrenheit advances sap collection forward on the calendar by 4.3 days.

The Impact of Climate Change on Maple Sugar Production

One way to look at the impact of warmer weather on forests is to analyze the average leaf-out date in the spring, when leaves come out on trees. The graphic below depicts average leaf-out dates for Vermont by year and decade, from 1991-2010. The plot shows that the average leaf-out date moved up from May 15th to May 10th when comparing between the 1991-2000 and the 2001-2010 decades.

One way to look at the impact of warmer weather on forests is to analyze the average leaf-out date in the spring, when leaves come out on trees.

While shifting maximum maple sap flow up earlier in the sugar season, warmer temperatures are also projected to shift the area of maximum sap flow farther north. Rapp  provide environmental modeling results that shift the area of maximum sap flow north approximately 250 miles, from near 43 degrees to 48 degrees latitude by the year 2100. The map below depicts these lines of latitude.

This shift moves the region of maximum sap flow from the United States to Canada, as the international border between Canada and the United States along the Vermont and the northeastern NewYork border runs along 45 degrees latitude. For this reason, predict a future world with flat to moderate increases in Canadian maple syrup production, contrasted with declines in yield for the United States. Both countries should expect substantial changes in the timing of peak sap flow.

Maple Syrup Season: Maple sap flow up earlier in the sugar season.

This projected shift in the maximum zone of maple syrup production could reinforce the strength of the maple sugar production in the Canadian province of Quebec, which has already become a powerhouse in this industry. Excellent environmental conditions combined with the immense size of this province has enabled Quebec to emerge as the epicenter of global production.

According to the Federation of Quebec Maple Syrup Producers, Quebec produces 72% of the world’s production of maple syrup, with production reaching 133 million pounds of maple syrup last season. This federation brings together 11,300 maple producers who work in more than 7,400 maple enterprises. If the projections of future growing conditions come true, Quebec’s hold on the maple syrup market may become even stronger in the future.

Quebec’s dominance in the maple syrup market made world news last month when it released nearly 50 million pounds of syrup from its supply in the Global Strategic Maple Syrup Reserve.This supply is the world’s only maple syrup reserve, started in 2000 to stabilize supply and pricing of this resource. The Reserve contained 100 million pounds of maple syrup at the start of the 2021 season, stored in 45-gallon barrels that cover an area equivalent to five football fields, in Laurierville, Quebec.

Global Strategic Maple Syrup Reserve: Laurierville, Quebec

Quebec released supply from the reserve because global demand remains high, while productivity declined during the last season due to the short sugar season and drought during the previous growing season in both Quebec and the northeast United States. Dry conditions in recent seasons match climate projections for increased drought in the region, according to the Vermont Climate Assessment.

The maps below show numerous years of dry weather in Vermont recently according to the U.S. Drought Monitor. Note that in the month of October during the years 2016, 2017, 2018 and 2020, at least part of Vermont observed moderate drought. Localized areas observed severe drought in 2016 and 2018.

If climate projections verify and the northeastern United States and Quebec face a future with increased drought, sugar makers would have to process a higher volume of sap to produce the same amount of maple syrup in upcoming years. Another climate characteristic that may reduce maple production is the reduction in average daily temperature range projected in a warming climate. This phenomenon occurs because cold things are warming up faster than warm things, according to Dr. Kosiba. This means daily minimum temperatures are warming faster than daily maximum temperatures, reducing the temperature range that is important for maple sap to flow.

Nonetheless, Kosiba shared good news at the end of her talk on climate change and maple syrup health. Although maple trees in the northeastern United States are projected to face increased stressors in the future, nearly all of Vermont will remain suitable for the growth of maple sugar trees. Changes in the woods will likely occur slowly, and response of trees to a changing climate will be localized, depending on factors such as soil type, elevation and aspect, or the direction a slope faces.

Whatever the future climate brings, Don Gale and his dog Maggie will tirelessly trek through the southwestern-facing slopes of their sugar bush during the upcoming seasons to produce high-quality, organic maple syrup. With his good sense of humor and positive outlook on life, Don will take the good and bad seasons in stride, as his operation continues to meet the demand for a timeless product that is delicately tied to the environment of a Vermont mountainside.

Author’s note: After interviewing Don Gale at Twin Maple SugarWorks, I could not resist buying maple syrup as gifts for family and friends. Through the magic of cyberspace, you can overcome geographic distance and order high-quality, organic maple syrup to be delivered direct to your home at this link:


Non-Linked References 

Vermont Agency of Agriculture, Food and Markets, 2020. 2019 Legislative Summary. Vermont Agency of Agriculture, Food, and Markets.

Kosiba, A., 2021: Sugar Maple Health and Climate Change, presentation at the Vermont Maple Conference, Friday, December 8, 2021.

Note: Most references have hyper-links embedded directly in the text. The two references that do not are listed above.

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