How can some trees survive in snowy, freezing cold climates but some can not?



How can some trees survive in snowy, freezing cold climates but some can not?

In: Biology

Trees get water from their roots. The way they get water up into the leaves and branches is by opening their leaves. You can kind of think if this as sweating. If you’ve ever had a drop of water fall on you when you stand below a tree, this is why. So when this happens the water from the roots get pulled all the way up so all parts of the tree gets water, but this also means some water is lost through these openings in the leaves.

In the winter, the air is colder and won’t be as humid. This means the air will be dryer than in the summer. Trees with big, flat leaves will usually let a good portion of their leaves die and fall off in the winter to conserve water or else they might lose too much.

Pine trees and evergreens adapted to have needle shaped leaves so they use very little water and therefore not need to let their leaves fall for every winter. They can also photosynthesize or make food in the winter too.

There are a couple issues with cold climates which make things difficult for plants.

The most obvious one is freezing. If the water inside a plant’s cells freezes, the ice crystals could rupture the cell and nuclear membranes of both the cell itself and the membranous organelles (mitochondria, chloroplasts), killing the cell. Creatures, including plants, evolved for cold temperatures handle this in one of several ways. For areas with light freezes, or where it doesn’t get too terribly below freezing, having high solutes in the cells will do. The reason salt melts ice is because dissolving stuff in water reduces its freezing point, and the same principle is at play here. Antifreeze chemicals produced by the plant can prevent it from freezing, saving the plant as long as it doesn’t get too cold.

What if it does get too cold? There are several ways to handle that. The most common is probably the tuber. Plants like potatoes and casava don’t grow highly energy-dense roots for nothing, they do it to save up energy during harsh conditions so they can grow back when things get better. The most hardy plants like this will be fine if the entire plant above the ground dies. They can just hibernate through the winter, and the stored energy can re-grow the leaves at the end to repeat the cycle next year. An additional bonus of this is that the underground stays a mostly constant temperature, so tubers don’t need to worry about freezing.

Other plants survive by having particularly hardy seeds which will only germinate after going through freezing. The entire population of adult plants dies every year, but it doesn’t matter because their seeds have already been spread.

Large plants like trees can insulate themselves with bark. The outer layer may freeze solid and die, but it doesn’t matter as long as the heartwood is fine, and it would take an incredibly harsh winter to freeze an entire tree out like that.

However, freezing isn’t the only issue for plants. Cold air holds water very poorly, which means leaves will hemorrhage water into the air through diffusion. This would dry out the plant very quickly…which is why trees lose their leaves in the winter. No leaves means no photosynthesis, but they can store enough energy in their massive root systems to last through the winter, and they don’t need to worry about losing water through bark. Evergreens like pine trees don’t need to do this because their needles are covered in a waxy substance which holds water in, and their high-density sap does not freeze easily.

All of these adaptations come with pretty severe costs, which is why you only see them in areas where they are necessary. Life finds a way, but if the way is easy it gets lazy.