Maureen Sexsmith-West ISA Certified Arborist, PR4600A
Keeping Trees Healthy despite Chinook Winters
I am not sure about other parts of the world, but this has been one of the colder, snowier winters I can remember for many years. We are still experiencing the occasional Chinook.
This is a weather system where warm, high velocity winds can cause temperatures to fluctuate from minus 20 to +12 Celsius within a 12 hour period. Winds are often 60-100 km hour. This combination of wind speed and temperature can result in 1 foot of snow vanishing in a day – partly melting, partly evaporating. As the weather fluctuates from very cold to very windy and warm, we can adapt our clothing, change our footwear and hide out indoors away from the elements. Even wildlife can find shelter. Plants are not so lucky. Rooted in place they must have ways of adapting and responding to cold and windy conditions. While your family pet puts on a thick layer of fur, trees shed their leaves to prevent freezing of their ‘water processing and transport system’. Trees can handle the odd frost but what is of greatest challenge here is the frequent freezing, thawing, freezing associated with Chinook temperature changes. The plumbing of broad leaf trees is very different than conifers.
Conifers Can Withstand Winter Chinooks
Evergreens use a valve system that allows the tree to regulate where and how much water moves around the tree in winter. The tubes (or pipes) are capable of withstanding expanded ice crystals when freezing occurs. Winter kill or winter burn occurs when needles lose more water than can be replaced by the root system. Evidence of this type of injury becomes obvious in Spring as needles turn brown and fall. The presence of cutin (a waxy coating) helps them retain as much moisture as possible.
Frost cracking is typical on the south side of broad leaf trees. This type of injury occurs most often on thin barked or young trees. Bark is exposed to direct sunlight, reflective sunlight and warm winds stimulating the water to begin moving. Sudden drops in temperatures at night can result in some water being trapped in the cells, freezing and expanding causing the tissue to burst. Repeated cracking is not uncommon and should be examined to determine if the crack is negatively affecting the safety or health of your tree. Contact our Certified Arborists to learn more about the trees on your site.