As towering trees release their leaves, a profound hush blankets the surroundings. Deciduous and evergreen trees alike must confront the twin trials of feeble winter sunlight and plummeting temperatures. While animals embark on southward migrations or embrace hibernation, bolstering their coats with thicker fur or feathers, altering diets, gravitating towards warmer enclaves at night, or finely tuning their body heat, trees stand firmly entrenched without recourse to such options. Remarkably, trees have charted their own distinctive course of survival strategies to navigate the rigors of the relentless cold.
Leaves serve as the dual role of solar panels and nourishment factories for trees. As the fall season approaches and trees brace for winter, they extract the majority of remaining nutrients from their leaves, a strategic move to safeguard these precious resources from being squandered amid the harsh winter chill. Remarkably, deciduous trees never entirely cease their leaf-shedding routine. Despite the suspension of photosynthesis and the subsequent hiatus in energy generation for a span of 5 to 6 months annually, the shedding of leaves bestows distinct benefits by mitigating the additional water loss incurred through foliar surfaces.
The intricate process of transpiration, marked by the release of water from trees into the atmosphere through evaporation, exacts a notable toll. An individual mature oak tree, boasting a foliage count of approximately 200,000 leaves, can relinquish a staggering 150,000 liters of water over the course of a year. In the verdant embrace of summer, trees shrouded in lush foliage imbue the environment with humidity, spanning from the crown to the base. This phenomenon contributes to an elevated temperature within the forested realm, juxtaposed with cooler and more breezy conditions in the adjacent areas.
In the realm of non-deciduous trees, such as conifers, a distinct set of adaptations comes into play. These trees exhibit minimal leaf surface area and feature a robust upper leaf surface adorned with a thick waxy coating, effectively curbing the pace of water loss. Additionally, these adaptations serve to slow down the process of transpiration. Unlike their deciduous counterparts, evergreen leaves lack the shedding attribute associated with broader, more expansive leaves, thus foregoing the same level of energy production efficiency. However, the continuous year-round photosynthesis that is a characteristic of needle-leaved trees makes up for this shortfall.
Certain pine varieties even exhibit an ingenious adaptation: the presence of antifreeze within their needles. This attribute equips them to flourish in icy conditions by means of a waxy substance situated at the “leaf” tip, mitigating moisture loss and protecting against cold-induced damage. The retention of leaves obviates the need for regrowth and conserves substantial energy with every approaching spring. Trees have evolved to thrive in nutrient-deficient soils and endure in challenging habitats. Notably, even needle-leaved trees and poplars possess the capacity to engage in photosynthesis via their stems when confronted with subfreezing temperatures. This energy generation stems from mitochondria, a component shared with our own biology, and contributes to sustaining cellular vitality.
Special Trunks in Trees
Within the tree’s trunk, the phloem and xylem cells play a pivotal role in orchestrating the transportation of nutrients and water throughout the tree. Over time, the aging xylem assumes the role of the solid core within the trunk, ultimately giving rise to the telltale rings that provide insight into the tree’s age. Although the protective outer bark serves to protect these essential cells, the potential harm that extremely cold temperatures could cause highlights their vulnerability. Trees dwelling in warmer climes can fall victim to sudden cold spells, whereas those inhabiting northern territories have devised their own strategies. The hardiest among them exhibit the remarkable ability to shield their cells, safeguarding them against temperatures as frigid as -40 ºC (-104 ºF).
This formidable feat is achieved through a distinctive biological adaptation. The formation of ice necessitates water molecules adhering to a particle’s surface, resulting in the crystallization of ice. Snow emerges when water crystallizes on airborne dust particles. Notably, these ice crystals possess sharp edges capable of penetrating cells, inducing their demise. However, cells within cold-resistant trees are devoid of particulate matter in their water and boast a smooth composition. Even if the water within these cells drops below freezing, the formation of ice crystals is circumvented.
Despite these adaptations, trees encounter limitations when temperatures plummet beyond -40 ºC (-104 ºF). Hence, the eerie cracking sounds emitted by certain trees in nocturnal forests find their explanation. In regions where temperatures descend below this threshold, tree species dwindle, and the survivors adopt an alternative strategy. These trees allow water to overflow from their cell walls, creating cavities within the cells. Consequently, even if ice crystals form, they remain outside the cell’s confines. Trees equipped to withstand temperatures below -40 ºC (-104 ºF) are identified as needle-leaved trees and bear distinctive cones containing seeds. Among them are the larch tree, white and black spruce, and balsam fir.
The number of coniferous tree species outnumbers their deciduous counterparts in the grand tapestry of tree diversity. In the northern reaches, the white birch reigns, accompanied by its kin, the trembling aspen, alongside the balsam poplar, constituting the sole pair of deciduous trees equipped to endure temperatures plummeting below -40 ºC (-104 ºF).
How Do Trees Survive the Winter?
Snow indeed has significant effects on trees, especially deciduous trees. Protection strategies against snow are crucial for them. Wet and heavy snow can lead to branches breaking or being crushed under the weight. Therefore, deciduous trees shed their leaves before the arrival of cold weather and snow. An early snowfall can be problematic for trees that still have leaves, as the weight of the snow can cause the leaves to remain on the branches and lead to branch breakage.
However, evergreen needle-leaved trees (conifers) respond to snow in a different way due to their long and slender needle leaves. Compared to the structure of a typical leaf, the surface area for snow adhesion is reduced on needle leaves, resulting in less snow sticking. These trees still get covered in snow, but they have flexible branches. These flexible branches, instead of breaking like rigid ones, bend under the weight of the snow. The flexible branches bent under the weight of the snow bent downward, causing the snow to fall off. Thanks to this mechanism, trees can withstand the weight of the snow throughout the winter, reducing the risk of being crushed or broken.