Sugar Maples and Climate Change
Can you imagine a Minnesota without sugar maples? Sugar maples are iconic to the big woods forests of central Minnesota, but our warming climate is leaving them exposed to increased stress and driving them out of the state altogether.
Why Do Sugar Maples Matter?
Sugar maples play an important role in the forests of Minnesota. Studies have shown that sugar maples help increase nitrogen cycling in the soil in which they live.
Why does this matter? Plants need nitrogen to help them grow. Bacteria in the soil decompose dead leaves and return nitrogen to the soil, which plants then use. Sugar maples help with this process, improving the overall health of our forests.
What Is Happening to Maple Trees?
In Three Rivers, and across the state, we are seeing a number of changes in our maple trees and maple forests due to warming winters.
Shorter Maple Syrup Season
The maple syrup season depends on temperatures rising above freezing during the day and falling below freezing at night. This change is what causes the sap to flow. With winters that are warmer and shorter, the season often starts and ends earlier. Learn more about the science and traditions of maple syruping.
Maple Forests Are Moving North
Over 100 years ago, maple forest was spread out across central Minnesota with its center of density near Brainerd. By 2003, the center of maple density was closer to Grand Rapids — approximately 60 miles north.
If temperatures continue to rise and snow amounts continue to fall, in another 100 years Minnesota may no longer have any maple trees.
Less Snow Cover to Protect Maples
Snow acts like a protective blanket in the winter. For trees, it protects their roots from injury in two situations:
- Extreme drops in air temperature
- Freezing and thawing on warmer winter days
Studies have show that trees whose roots did not have snow cover protecting them did not grow as fast as those that did. As our maple trees grow slower and become more prone to injury, fewer can be safely tapped to make syrup.
Fewer Red Leaves in the Fall
Leaves change color in the fall in response to cooler temperatures and shorter days. While the length of our days isn’t changing, the temperatures are. Warmer nights cause trees to delay their color change, and some may not make certain colors at all.
Trees that produce red colors in the fall, like sugar maples, might store the sugars used to make red pigment in their twigs — or just burn them off completely. If this happens, our autumn color shows might not be as spectacular for future generations.
Warmer winters and longer growing seasons mean that more white-tailed deer survive winter. As deer populations grow, they are eating more maple seedlings and saplings. This makes it much harder for new trees to grow.
How We're Adapting
In Three Rivers, our Forestry department is already taking steps to adapt to these changes and prevent further damage to maple trees.
- We avoid stressing existing trees. During construction and trail maintenance, we take extra precautions to ensure we do not damage maple trees in the area.
- We do not tap stressed or injured trees. Tapping an already stressed tree for maple syrup can worsen its overall health.
- We will plant seeds harvested from warmer climates. Each year, our Forestry department plants thousands of saplings in our parks as part of our reforestation program. While most seeds we use come from Hennepin County, in the future, about a third will come from Iowa, where the trees are adapted to a warmer climate.
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By: Paul Kortebein
Sugar maples are one of the most well-known native trees around the Twin Cities, but how much do you really know about them?