Sugar Maples in an Age of Climate Change

Sugar Maples in an Age of Climate Change

Illustration by Adelaide Tyrol

Unlike the Ents in Tolkien’s Lord of the Rings, real trees can’t walk away from danger or fight their own battles. When climate becomes inhospitable, forests can only shift ranges over long periods of time. This isn’t a problem when natural climate change occurs slowly. At the end of the recent post-glacial period, it took 4,300 years for the ice sheet to melt back from Middletown, Connecticut, to St. Johnsbury, Vermont — averaging 245 feet a year. Forest communities in front of the glacier gradually migrated northward in its wake.

Starting about 9,000 years ago and stretching for the next 4,000 to 5,000 years, the average temperature in the New England area became nearly 4°F warmer than it is today, and the climate was similar to modern-day Virginia. Hemlock and white pine grew 1,300 feet higher up the mountain slopes. Evidence now shows that the engines of the industrial age are taking today’s climate forward, into the past. U.S. Climatological Network Data reveals that the mean annual temperature has increased by 3.8°F since 1835, but 70% of this rise in temperature has occurred since 1970.

Barry Rock, Professor of Natural Resources at the University of New Hampshire in Durham predicts that, based on two climate models in a New England regional climate assessment study, “Within the next 100 years, Boston could have a climate similar to either Richmond, Virginia, or Atlanta, Georgia.” These computer models project that the average regional temperature will rise from between 6°F and 10°F over the next century.

If the models prove accurate, Rock says that, “In 100 years, New England’s cooler regions will no longer promote the growth of sugar maples, which are well adapted to the region’s current climate. This climate will support species that now grow to the south and in lower elevations, especially oaks and southern pines. On average, trees can only move their range from 10 to 25 kilometers over a 100-year period, and the current rate of climate change will not allow enough time for trees to ‘migrate’ northward in a smooth transition.”

Ultimately, under this scenario, the optimal range for sugar maples in New England could retreat up the high mountain slopes and to northern Maine. (Sugar maple’s current range extends as far south as Virginia and Tennessee, though only in the higher mountains.) Of the five computer models created by the U.S. Forest Service to predict the geographic shift in the ranges of forest species, only one foretells that global warming will cause sugar maples to disappear completely from parts of New England. Even if the climate warms considerably, our forests will still support the growth of some sugar maples, especially in higher terrains.

Although the range of sugar maples changes slowly, the flow of sap in a sugarbush is dynamic and depends on fine temperature variations that occur daily throughout late winter and early spring. Sap flows best when nighttime temperatures drop into the mid-20’s and when daytime highs reach around 38-40°F.

From here the effects of climate change are harder to predict. If the daily cycling between freeze and thaw occurs less frequently, sugaring will suffer, as it will if the season is shortened by several weeks. But if sugaring as we now know it is simply shifted earlier into the year, the effect could be less pronounced. Making predictions about sugaring season has always been an uncertain but popular pastime, even before the dawn of climate change.

The maple sugar industry can compensate somewhat for the uncertainties of the shifting climate. According to Dr. Timothy Perkins, Director of the University of Vermont’s Proctor Maple Research Center, “The best equipment in the sugar house isn’t going to make you any more money. It’s how you manage the sugarbush that counts.” Producers need to tap their trees earlier, before the sap starts to flow, so they can gather the best quality sap of the season. Old tubing must be replaced with new, which is made of superior material and is more efficient. Getting rid of leaks in the system will help, as well as using a vacuum system for collecting sap. Collectively, these steps can help mitigate the problem.

No matter what steps are taken, the wheels have been set in motion. The question is: How far down the road will sugar maples have to travel before we put the brakes on climate change?

Michael J. Caduto is an author, ecologist, and storyteller who lives in Reading, Vermont.

  1. W.B. Leak
    Mar 25, 2011

    Possibly we should temper these results by the years of migrational research in New England showing no appreciable change in elevational/geograhical distribution as well as the role of migrational theory. Leak,2009, North. J. App. For. 26:164-166; Leak and Yamasaki,2010,Northern Res. Station Res Pap. NRS 13;Leak and Smith, 1996, For. Ecol. Man. 81:63-73; Solomon and Leak, 1994, Northeast. For. Expt. Sta Res. Pap. NE-688; Solomon, Leak, Hosmer,1997,NATO ASI Series I 47 Springer-Verlag; Leak and Graber, 1974, Ecol.55:1425-1427.

  2. Chuck
    Apr 05, 2011


    Thanks for your comment. We’ll take a look at the papers you mention.

    Climate change is a topic that we struggle with mightily and, amongst us editors, heatedly. It’s clearly the most significant ecological story of our time. It’s also a story replete with hyperbole and mis-information. We need to cover the story yet we aren’t always sure how to do it accurately. In the case of maple migration, it’s possible that the migration has yet to occur because climate change has only just begun to take hold. It’s also possible that no significant migration will take place because other factors are more significant controls on the species’ distribution than climate.

    Either way, thanks for looking out for us and helping to point us in the right direction.

    —Chuck Wooster

  3. Robert M.
    Mar 07, 2014

    For people like me that believe that the climate is changing, and will always change at a rate slower that those that will be dead before they know the change was in fact slower than expected. For the climate changes very, very slowly and sounding the alarm of impending catastrophe by making statements, for example, that “Boston’s climate will be similar to Atlanta’s” is ridiculous and only serves to anger those of us that simply believe for good, rational reasons that the variations we are seeing in the weather over the past one to two-hundred years is simply noise and means nothing in the scope of actual climate change which is occurring slowly over periods of thousands of years. What’s the big deal that mean temperatures have increased by 3.8 degrees since 1835 and that 70% of that increase happened since 1970. I mean, that’s weather folks. 1970 is about half of the 88-year normal solar activity cycle. We all know that the Earth has been getting warmer since the last ice age. It’s going to get “permanently” warmer but it’s going to take thousands of years more for that to happen.

    Please just stop discussing the weather as if it were climate change. Climate change occurs over thousands of years and anything that happens in less time than that is the weather. If the weather is changing Mother Nature will fix it (and anything that’s messing with her) in the next hundred years or so. We have nothing to worry about and there is nothing we can do about it, nothing, and articles like this are what you can read in any end-of-the-world environmentalist rag. I thought Northern Woodlands was above that noise.

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