How Woody Plants Manage the Shifts from Fall to Winter to Spring

 By Richard B. Primack

 

“I frequently tramped eight or ten miles through the deepest snow to keep an appointment with a beech-tree, or a yellow birch, or an old acquaintance among the pines.” Henry David Thoreau inWalden, p. 288.

 

 

In a recent article in the Old Farmer’s Almanac Garden Guide, I describe how trees survive the extreme cold weather of the northern climate.  

In autumn, woody plants start preparing for winter. When their leaves change color and drop, their twigs, branches and trunks start to lose water. As a result, their cells contain higher concentrations of sugars, salts, and organic compounds. 

Photo 1: In autumn, woody plants lose their leaves and prepare for winter.

This change lowers the freezing point of the cells and tissues and allows them to survive temperatures far below the normal freezing point of water. 

Photo 2: Trees have the ability to survive months of cold and snowy weather.

 

In the late winter and early spring, trees and shrubs have three ways to know when it is time to re-hydrate their tissues and start growing again. 

First, plants can stay dormant until they have experienced a certain number of cold winter days. They count these cold winter days to avoid being fooled into leafing out on abnormally warm days in January and February. 

Second, plants sense spring warmth. After they experience a certain number of warm days each spring, their buds start to swell and then they leaf out and flower. 

Third, plants also sense daylength or photoperiod. As days get longer in the spring, trees get itchy to leaf out and are quick to grow in response to warmer weather. 

Warming temperatures driven by climate change is making it harder for many species to detect how to avoid or handle winter cold and spring frosts. Warmer temperatures can fool trees such as apples and pears into leafing out and flowering several weeks earlier than normal, increasing their vulnerability to late frosts and damaging fruit production. Gardeners and farmers need to be aware of these climate change risks when deciding what trees and shrubs to plant. 

Photo 3: Unpredictable late frosts sometimes damage flowers and young leaves.

In coming decades, many cold-loving evergreen tree species (such as spruces and firs) in the northern United States and Canada will become less abundant when climate change challenges become too much for them to bear, and they will be replaced by deciduous species, such as maples and beeches. In turn, forests currently dominated by maple and beech trees will be gradually occupied by native species from farther south, such as oaks and hickories. 

 

Photo 4: Future northern gardens might include plants originally from warmer climates, such as figs and crepe myrtles. 

Here is a link to the article: LINK