For thousands of years, making maple sugar and syrup has been a spring ritual valued for its health, cultural, social and economic benefits. In the face of climate change, however, there are concerns that these values—and the trees and forests that provide them—might be in danger. In this blog post, we’ll discuss the potential impacts of climate change on sugar maple trees (Acer saccharum) and mention what can be done to mitigate those impacts. Although our focus is on the sugar maple, the most desired tree for production, it is important to note that sugar/syrup can be made from all maples, including the commonly tapped red maple.
There are three primary potential impacts of climate change on maple sugar/syrup production:
- The shift in range of sugar maple trees
- Changes and variability in the season along with a decrease in sugar concentration in sap
- Abundance and presence of invasive species
Sugar Maple Range
Sugar maple exists in a fairly narrow range with Wisconsin toward the northern and western end of that area. The trees can be found throughout Wisconsin, with the highest densities in the Driftless region in the southwest and the northern one-third of the state. Computer models that simulate the impacts of a changing climate on tree distribution have suggested that over the coming century, the range of sugar maple will shift northward and exclude areas in southern and southwestern portions of the current range (Giesting, 2020). That said, sugar maples will likely remain in Wisconsin for the coming centuries. So, the loss of sugar maple is less of a concern than the other potential impacts from climate change.
Sap Season and Sugar Content
As expected with a warmer climate, and, in many cases already experienced, the season for collecting maple sap will shift to earlier in the year. Projections based on collected data and climate modeling indicate that the sap season will be a month earlier by the end of this century compared to what it has been historically (Rapp et al., 2019). This isn’t necessarily expected to have much impact on maple syrup production by itself. However, with this shift to an earlier season, there is also projected to be more variability in the weather, which would likely lead to more variability in annual production, particularly in the southern and northern edges of maples’ range (Rapp et al., 2019).
The biggest potential impact on maple syrup production, though, is from the potential decrease in the sugar content of sap. With longer growing seasons, the trees are able to produce more sugar; however, they also grow more, consuming more of the sugar they produce. The net result is that sugar maples (and likely the other maples) will have lower sugar content in their sap in a warmer climate. Modeling suggests that around a 30% decrease in sugar content can be expected overall, and, again, more variability between years (Rapp et al., 2019).
Invasive species (emerald ash borer, Dutch elm disease and chestnut blight, for example) can have a devastating impact on trees. We have been fortunate so far that maple trees have not been severely affected by any particular invasive species, although there are localized impacts on tree regeneration from garlic mustard and buckthorn. With a warming climate, there is potential for the introduction of new species or expansion of existing invasive species. For example, Asian longhorned beetles have been in North America since the late 1990s, but recent modeling suggests they will be able to expand their range in a warmer climate (Zhou et. al., 2021).
What Can Be Done?
Perhaps the most important thing to do in the face of climate change is to ensure maple forests are healthy and to continue to monitor forests for changes. Management that minimizes competition between trees leads to improved health of individual trees and increases sap production and sugar content. In addition, maintaining a diversity of tree species and forest floor species will help ensure the long-term health of the forest. And, watching for invasive species to catch any infestations early and working to manage their populations will help minimize their impact.
Rapp, J.M., Lutz, D.A., Huish, R.D., Dufour, B., Ahmed, S., Morelli, T.L., & Stinson, K.A. (2019). Finding the sweet spot: shifting optimal climate for maple syrup production in North America. Forest Ecology and Management, 448, 187–197. https://doi.org/10.1016/j.foreco.2019.05.045
Zhou, Y., Ge, X., Zou, Y., Guo, S., Wang, T., Zong, S. (2021). Prediction of the potential global distribution of the Asian longhorned beetle Anoplophora glabripennis (Coleoptera: Cerambycidae) under climate change. Agricultural and Forest Entomology, 23(4), 557–568. https://doi.org/10.1111/afe.1246 1