Tree Talk: Winter is here

WINTER. If this season is defined by cold, snowy weather – then we have arrived. The local weather reports warn us to protect our bodily extremities (our head, hands and feet) from exposure, risking the chance of frostbite. With the harsh temperatures, how are plants on the Northern Plains able to survive?

The process for woody plants acclimating to winter begins in late summer as the days become shorter. Fewer hours of sunlight and cooler temperatures trigger the loss of chlorophyll (one of the magic ingredients involved with photosynthesis) in deciduous leaves, and the colors of fall foliage are exhibited. What we don’t see are additional changes at the cellular level, where water is replaced with sugars and proteins – forming a type of antifreeze to protect woody plants during the long, cold winter.

This process enables trees to endure temperatures as low as -40 degrees F, but there are native trees that are able to survive even lower temperatures by self-dehydrating, further reducing the cellular water content. The last part of a tree to harden are the roots – the roots are less hardy than the above-ground parts of the tree. Soil temperatures below 10 degrees F are fatal to most tree roots, but this year (the winter of 2021-22), we have a generous layer of snow. Snow very effectively insulates roots from frigid winter temperatures.

While species diversity is one of the best defenses to protect trees from destruction via exotic pests, we’ve relied on native species that Mother Nature has selected to survive the weather extremes of the Northern Plains. Research continues to reveal new types of trees that are hardy and worth the investment of planting in parks, along community streets, and on private property. It’s a fine balancing act – selecting plants that work here - and it is something that continues to evolve.(See: NDSU’s Woody Plant Improvement Program, which has released more than 50 hardy “new” trees over the past sixty years of research in North Dakota, currently under the direction of Dr. Todd West).

In the meantime, here are some of the hardiest trees that have proven ability to withstand the harsh extremes of North Dakota’s seasons – if planted in the right locations: Paper birch, Eastern redcedar, Siberian larch, Siberian crabapple, Black Hills spruce (aka white spruce), quaking aspen, bur oak and American elm. The best plan is to continue to plant and to sprinkle newly “discovered” plants that will work here, too.

Yes, winter is here – but the days are already getting longer!