Tree Talk: Winter is here

WINTER. If this season is defined by cold, snowy weather – then it arrived nearly two months ago, long before the astronomical calendar-date of winter's start on December 21. Local weather reports warn us to protect our bodily extremities (our head, hands and feet) from exposure, to reduce the risk of frostbite.

When it's bad enough outside, many of us can make the choice to hunker down inside. With the wind and harsh temperatures, how are trees on the Northern Plains able to survive?

For starters, trees have bark. Bark provides some insulation and protection from the elements.

More importantly, woody plants acclimate to winter beginning in late summer, triggered by fewer hours of sunlight and cooler temperatures. Deciduous trees drop leaves to reduce water loss.

Conifers retain their leaves (needles) which are better at retaining water due to small surface area and a waxy outer coating.

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 is 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 2022-23), we have a generous layer of snow. Snow very effectively insulates roots from frigid winter temperatures. Looks like roots will be well-protected this winter.

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 research that continues to evolve. (See: NDSU's Woody Plant Improvement Program, which has released more than fifty hardy "new" trees over the past sixty years of research in North Dakota, currently under the direction of NDSU's Dr. Todd West). Some of the best and hardiest available trees include 'Prairie Expedition' American elm, 'Northern Acclaim' honeylocust, 'Prairie Stature' bur oak, 'Prairie Torch' Ohio buckeye, 'Prairie Dream' paper birch...the trees are named to denote their origin and rightful place to exist, even here on the cold northern plains.

The best plan is to continue to plant reliably cold-hardy trees and to sprinkle newly "discovered" plants that will work here, too. Yes, winter is here – but the days are already getting longer! For trees, it's just Mother Nature running its course.