Trees and Climate Change – It’s Complicated

climate change affecting forests

By Anne Foreman

How is climate change affecting our forests?

Telltale signs that forests are changing are everywhere. Warmer winters and drier summers with unpredictable rainfall are bringing more intense insect plagues. These plagues can kill trees in just a few years. Link to information about the mountain pine beetle.  Droughts leave forests more and more susceptible to wildfires.

The Case of Maple Syrup

climate change affecting forests
Maple syrup production has decreased as moderate winter temperatures have increased.

Climate Change is already affecting maple syrup. Maple tree owners boil maple sap to make maple syrup. Native Americans invented maple syrup long before Europeans arrived in the Americas. It is now a signature crop in Canada.

Maple trees require specific temperature conditions to produce sap that flows – daytime highs above freezing with nighttime lows below freezing. These conditions have historically occurred for 6 to 8 weeks, two times a year – when winter turns to spring, and again when fall turns to winter.

The Fulton family is seeing big changes in sap yield.  The Fultons are fourth generation maple syrup producers in Ontario, Canada. In 2012, for example, the sap in their maple trees flowed for just 13 days instead of 6 to 8 weeks because the temperatures weren’t right.

The Case of Forest Profiteers

Most wood sellers aren’t putting careful thought into the effects of climate change, according to Chris Swanston of the U.S. Forest Service. He says real-estate investment trusts and other financial entities own a majority of today’s timberland. These investors are more interested in short-term profits than sustainability. As a result, profit now trumps long-term forest health.

Putting Foresight over Profit

One forest owner is thinking about the future. John Rajala owns 22,000 acres of northern pine and hardwoods in Minnesota. He has a “300-year plan” for managing his trees. Rajala leaves a lot of trees on the land to reseed the forests with good genetic stock. He also plants a variety of trees as a hedge for a warmer climate in the future. Rajala reasons that if some species do badly in a warmer tomorrow, others will flourish.

climate change affecting forests
As global temperatures rise, forest fires have grew in size and frequency.

The U.S. Forest Service is also thinking about how climate change is affecting forests. Four years ago, the Service began running experiments at five sites around the country to try to answer the question of how best to help woodlands adapt to climate change. 

Four approaches are being tested: (1) passively letting nature take its course; (2) thinning and managing mostly native trees along traditional lines; (3) growing a mix of native species with some coming from 100 miles to the south; and (4) the most radical one, bringing in non-native trees from warmer, drier areas in nearby states. This fourth experiment is basically what Rajala is doing in Minnesota. For more information about adaptation approaches.

What’s the “Right” Answer? Well….

So, is planting non-native trees the answer, trying to anticipate future climates? Most trees can migrate only as fast as their seeds disperse. There is no way that trees can “outrun” climate change.

The scientific community is divided about the wisdom of planting non-native trees in any environment. No one knows the unintended consequences might be of shuffling trees around. Moving species is the equivalent of ecological gambling, some scientists say. Other scientists say we can’t wait to try experimenting until we know everything.

So, what’s the bottom line for ensuring forests for future generations? Well … it’s complicated.

Courtesy of the Rossmoor News, June 12, 2019.  Email Anne Foreman at

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