Wed. Nov 29th, 2023
balsam fir

What did one tree say to another on a snowy winter day?

“My feet are cold…”

“What feet?”

Okay, they may not regret it, but what do What do trees do in winter?

They cannot go south; They are stuck in one place. They cannot find a cozy den and hibernate. They just have to stay there, outside, in the weather and tough it out, no matter the cold, the snow or the wind.

Winter is a time of scarcity: it is difficult to get food. It’s cold (sometimes very cold) and the cold saps energy and heat. It’s also dry. Despite the snow, the humidity is lower and living beings dry out.

Snowshoes in a forest.

Animals have several strategies that help them cope with winter. They fly south, hibernate, or grow thick fur or feathers. They change their diet, seek warm places at night or regulate their body temperature.

magnolia warblerMany birds, like this magnolia warbler, fly south to the tropics to spend the winter.

Trees have their own strategies to survive in this harsh climate.

How trees fight the cold: leaves

The leaves are the tree’s solar panels and food factories. Sunlight, water and nutrients from the soil become food for the tree.

In the fall, trees extract the most remaining nutrients from their leaves. If they didn’t, those nutrients would be lost due to the extreme cold of winter.

Green maple leaves.Deciduous trees, like maples, draw nutrients from their green leaves in the fall and then let them fall before the snow flies.

Leaves fall to the ground.

In the case of evergreen plants, such as pine and spruce, the leaves have become long, thin needles. These needles are covered in a waxy substance that reduces moisture loss and damage caused by low temperatures.

Evergreen trees keep their “leaves” all year round, which saves them a lot of energy each spring since they don’t have to make new ones.

Fir needles and branches.Evergreen trees like white spruce have fine needles instead of leaves that have a waxy coating that protects them from winter weather.

It also means that they can thrive in soils that have fewer nutrients and live in habitats where other trees cannot or do not perform as well.

tree trunk in winterThe green bark of this poplar can produce some food (through photosynthesis), even at a few degrees below zero.

In fact, evergreen needles (and even the bark of some trees like cottonwood) can still produce food through photosynthesis, even when temperatures are below freezing!

The energy source of all cells, including ours, is called mitochondria. It’s not a lot of energy, just enough to maintain the health of the cell, but the mitochondria of cells exposed to light can still make some food at temperatures even a few degrees below zero.

How trees fight the cold: wood

Trees are like huge drinking straws. They are long, tall and mostly straight, and need to receive food and water along their entire length, from roots to leaves and from leaves to roots.

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To do this, they have two types of specialized cells under their cortex that form something similar to a tube. The first, called xylem, moves water and dissolved nutrients from the roots to the leaves. The second, called phloem, transports the food produced by the leaves to the stems, trunks and roots.

These tubes of cells surround the entire tree, just below the bark, and run throughout the tree, from the roots to the leaves.

A close-up of tree growth rings.The tree’s dark outer bark protects the phloem and xylem beneath. Old xylem becomes the solid wood of the tree as it ages, producing “growth rings.”

The extreme cold of winter can damage these cells, meaning the tree could die of thirst and starvation if the damage was severe enough. Trees that live in warmer climates can be damaged by a cold snap. But trees adapted to northern climates have strategies to combat the cold.

“Tough” trees that can withstand cold temperatures, down to -40°C, do so through a process called “supercooling.”

For ice to form, water molecules that are below the freezing point need a particle or surface on which to grow crystals. Snow needs dust particles in the air to begin crystallizing and forming snowflakes. Water crystals are deadly to living cells; They are sharp and will pierce cell walls, killing them.

Cold-hardy trees have cells without particles in their fluids and are soft inside. So while the water in cells can reach subzero temperatures, it cannot form crystals.

A winter tree landscape.Hardy northern trees, such as aspen, spruce and birch, populate the forest of Windy Lake Provincial Park

However, below -40ºC, even the water in cells adapted for supercooling will freeze, killing the cell. Therefore, on very cold nights, you can sometimes hear the creaking of wood in the forest. Trees that grow in places where the temperature drops below -40ºC need another strategy to survive.

As you travel further north, into the Boreal Forest and beyond, the number of tree species becomes smaller. This is because there are fewer species hardy enough to adapt to temperatures below -40ºC. They do this through a process called “extracellular freezing.”

White PineA mighty white pine sleeps during the winter in Marten River Provincial Park (Temagami)

If the water in the tree’s cells remained in the cell below -40°C, the ice crystals would rupture the cells and the tree would crack and die. Instead, water oozes from the cell walls into the cavities between the cells. When water freezes, ice crystals cannot pierce any cell walls and damage the tree’s vital xylem and phloem.

Trees that can survive temperatures below -40ºC are a select group. Coniferous trees (those whose seeds come in cones) that can withstand extreme cold include jack pine, tamarack, black and white spruce, and balsam fir.

The number of deciduous tree species (trees that lose their leaves each autumn) is less than the number of conifers. White birch grows throughout Canada, even in the far north. Aspen and balsam poplar are the only two other deciduous trees capable of withstanding temperatures below -40°C.

How trees beat snow

Snow is another winter enemy of the tree.

The tree to the right of the snowshoe has cracked due to snow and wind from a winter storm in Windy Lake Provincial Park.

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The snow is heavy and, in warm temperatures, wet snow can be very heavy. Deciduous trees lose their leaves due to snow and cold. The first snowfalls in late fall often cause significant damage to trees that still have leaves on their branches.

snowshoes in the forestEvergreen tree branches shed their snow onto a snowshoe in Windy Lake Provincial Park

Evergreens keep their needles, so they have to deal with snow differently. They are long and very thin, so snow doesn’t stick to them like it would with a normal blade. However, evergreen needles and branches still accumulate snow during storms and often in colder snowy places.

Many evergreen trees have branches that are flexible. They bend under the weight of heavy snow and instead of breaking, as stiff branches do. Flexible branches that bend downward can also shed snow, meaning they don’t have to carry that weight all winter.

Trees share their winter adaptations

Trees can survive winter even when they have to remain exposed to the cold. They have to; They are too big to hide and can’t move anyway.

Animals, on the other hand, need a sheltered place at night and during winter storms.

A woodpecker was looking for a beetle under the bark of a tree.A woodpecker looks for beetle larvae under the bark of a tree.
A black-backed woodpecker pokes its head out of its roosting cavity.A black-backed woodpecker peeks its head out of its roosting cavity

Trees come to the rescue.

They provide shelter to many animals in winter.

Insects hide under the bark of trees until spring arrives.

A red squirrel looks out from a hole in the treeA red squirrel looks out from its new home: a woodpecker nest

Woodpeckers hunt beetle larvae under the bark of trees during the winter months and maintain elevated homes in holes they excavate in tree trunks.

In southern Ontario, squirrels build large nests of leaves and branches high in a tree to spend the cold winter nights. In northern Ontario, however, squirrels use abandoned woodpecker nests.

On very cold nights, the black-capped chickadee, one of the few birds that remains in the northern forests year-round, gathers with other chickadees in tree cavities for warmth. They can even go into mini hibernation.

A black-capped chickadee perched on a branch.The black-capped chickadee seems to find its voice in the winter as one of the few songbirds that remains in the northern forests year-round.

Both chickadees and Canada jays use tree bark as a freezer to store food during the winter when times are tough.

Birds make food caches under the bark of trees (spruce seems to work best) and tree bark has chemical properties that help preserve food and retain more nutrients.

A Canada Jay perched on a branch.The Canada jay is a northern bird well adapted to cold winters.

Look at those sturdy trees

Winter is a harsh season. That’s why most animals (and even some people) overlook it. They fly south, hibernate or are simply born in spring.

Trees have no choice, but some special northern trees have developed ways to safely overwinter and wait for the first days of spring.

The Moose Ridge Trail in fall.The Moose Ridge Trail looks south into the boreal forest of Halfway Lake Provincial Park

You can hike through the forests of these hardy northern trees at parks like Halfway Lake, Nagagamisis, Kettle Lakes, and Esker Lakes during the camping season, or visit Windy Lake in winter and snowshoe or ski through the silent sleeping forest. .