March is one of my favorite months of the year. The longer days, melting snow, and warmer temperatures draw everyone out of their homes after months of hunkering down indoors to cope with frigid wind chills, short days, and dark nights. In my other life as a naturalist at Warner Nature Center near Stillwater, March is also the time when we tap the maple trees to harvest sap to turn into maple syrup.
I love that there are so many facets of maple syrup production to explore. I love the connection to the biology of the maple trees sending sap stored for the winter up to their new buds. I love that maple syrup is a food native to North America, produced here by American Indians long before European settlement and to this day only produced in North America. I love the culinary potential of maple syrup as sweetener (try it on popcorn!). On a more basic level, I love the smell of wood smoke mixed with the steam that comes off the evaporator as maple sap is boiling.
Collecting maple sap requires a specific set of weather conditions: temperatures must dip below freezing at night and rise above freezing during the day. Maple trees send stored sap up to their new leaf buds, and that sap freezes in the air-filled cells of the maple tree’s sapwood. This causes the tree to suck up more sap stores from its roots (for a more detailed explanation, see this article). So, the sap we collect after a thaw could be running up to the leaf buds or back down through the cells due to gravity. Maple trees also need snow cover to protect their roots from freezing.
This year, we tapped Warner’s sugarbush in early March and watched eagerly as we waited for sap to drip down the spiles into the “sap sacks” hanging from them. For the first two weeks, sap barely dribbled out as temperatures rose into the unseasonably warm. Only in the last week of March the sap really started to flow, when the weather hit the “40-20” sweet spot described by syrupers. That is, temperatures were in the 40s during the day and the 20s at night, causing sap to flow up and down through the sapwood more than when the temperatures were consistently above 40 degrees.
As we experienced unseasonably warm temperatures this maple syrup season, I wondered if the magic of maple syruping will be something that future generations will also be able to enjoy. Although it is impossible to attribute any one weather event to climate change, it is on my mind as we experience unusual weather patterns and extremes in Minnesota. Climate scientists agree that climate change will cause less predictable weather and more weather extremes. It is easy to imagine that we will continue to see unusual weather patterns as winters turn to springs, and that the already short six-week maple syrup season could grow shorter and arrive earlier as our planet warms. Warmer temperatures and erratic weather patterns could also put maple trees under stress, causing them to shed their leaves prematurely and thus not store as much sap.
Maple syrup is only produced in Canada, the Northeast, and the Upper Midwest. Maple trees grow in other parts of the world, but nowhere else has the temperature swings required to collect sap in the early spring. A USDA Forest Service report predicts that sugar maples will lose most of their suitable range in the eastern U.S. in the next one hundred years, although the trees may still be present in lower numbers. This will likely negatively affect maple syrup producers, driving maple syrup supply down and prices upward.
Figure 2. Current extent of Sugar Maple in the U.S. and projected extent in 2100
Climate change is an ever-looming threat, but an abstract one. We aren’t often faced with the reality of its effects on our day-to-day lives. Perhaps one of the first tangible effects we’ll feel will be on our food supply, when agricultural commodities that are dependent on certain climatic conditions, like coffee, chocolate, and maple syrup become scarcer.