Tuesday, December 29, 2020

The World of Winter Trees

Frozen trees in a field of snow. Lake District National Park, UK. By Click & Learn Photography.
Winter may seem like a dead time for tree lovers, but there really is a lot going on in the world of trees at this time of year. For trees, this is just another part of their yearly cycle. There are particular trials for winter trees, but also a lot happening out of sight. Evergreens have their own way of doing things in winter, but for the purposes of this blog, I want to explore the cold-weather life of deciduous trees.

Tall silhouettes of trees surround a dark path with orange leaves on wither side of it. By Bernd Schulz on Unsplash.
Trees begin preparing for winter months before cold weather and snow move in. Part of the transition is one that we can all see and appreciate, the magnificence of autumn trees. Green leaves contain chlorophyll, which not only gives them their color, it also feeds the tree through photosynthesis. During the winter trees will live off the food they have stored in the summer, so they will not need their leaves. They stop making chlorophyll, the green color disappears, and latent colors appear. The colorful leaves soon fall off entirely, relieving the tree of the need to provide the water and the mechanics of photosynthesis that leaves require. The tree is then able to focus its resources on its other parts. Losing their leaves is one way trees protect themselves ahead of winter dryness. They also move water around in their cells to protect them from freezing and to keep their nutrients intact. Read more on this here.

Water is a big issue for trees in cold winter climates. They cannot depend on the soaking rains from other times of the year, and when moisture does fall it is often bound up in snow. Moisture is moisture, one might think, but frozen water is very difficult for trees to access. If you are tending trees, water them when temperatures are above 40°F and there’s no snow, and use a product like Hydretain that holds water in the root zone. Here’s an article on watering trees at this time of year from the city of Greeley, Colorado, where they know a thing or two about winter weather. 

A pine branch encased in ice. By Sarah Cervantes on Unsplash.
Water is at the root of another problem for winter trees – the risk of exploding. Although it sounds very dramatic and catastrophic it is only one of those things. Trees can make a sound like a gunshot, which is pretty dramatic and definitely unsettling, but this phenomenon does not cause the tree to experience a bomb-like phenomenon. They crack (both physically and audibly) instead. This is caused by water freezing and expanding inside the tree (more on the science of it here), creating a rupture in the bark of the tree. This sort of thing happens in sub-zero weather in areas where native trees are winter-adapted, so they are generally able to shake off such cracking (more here). Check out this video, to see an “explosion” for yourself. 

Snow-covered trees in a line on a blue field with a blue background. By Tomas Tuna on Unsplash.
Internal ice is not the only thing that poses a problem for tree bark. Sunscald (sometimes called Southwest Winter Injury) can get them, especially if they’re younger trees. Sunscald happens when there are warm, sunny days and then cold winter nights. During the day the sun heats up the bark, causing the cells to open up and activate in response. Once night falls, freezing temperatures can damage the newly-opened cells. The end result can be bark cracks and even damage to the wood underneath the bark. There’s not much you can do once this happens, but proactive treatments include wrapping the tree or applying protective paint. We carry both wraps and paint

A deer face to face with a carrot-nosed snowman.
Wrapping a tree not only protects it from sunscald, it can offer some protection to the bark from animal damage. During the fall and winter, all sorts of critters want to feed off of, rub onto, or otherwise prey on your trees. Here is a brief article from the Chicago Tribune that explains the most common animal culprits and ways to ward them off. If you didn’t get around to wrapping your tree, or you didn’t want to, or if you did and want more protection, animal repellents can add another layer of care for your trees. We have a variety of great repellent products (see here) that can help with whatever is pestering your trees without resorting to toxic chemicals. 

Close-up of the red and orange bark of a Tibetan Cherry Tree.
Tibetan Cherry Tree 
Damage from weather or animals aside, bark can be a compelling sight on a winter tree. Some trees undress just enough in the winter for you to see the pretty wood they are hiding under their bark. There are those that hide their beauty behind their foliage and there are those that exfoliate their outer bark in winter and surprise you with the beauty beneath. Here and here are some gorgeous examples.

Despite all the hardships that the season can bring, trees do a lot of work in the wintertime. It’s just doing all the work out of sight underground, so it is hard for mere humans to observe and appreciate their efforts. This article explains (as well as scientists can determine) what’s going on down there in the root world. Basically, their goal is to spread out and strengthen before spring comes so that they have the resources they need for robust aboveground growth. This plan seems to work most of the time, unless there is an exceptionally hard frost that penetrates deep into the soil or the soil is disrupted by frost heaving. Frost heaving occurs when soil freezes and the ice moves towards the surface. This can weaken trees to the point where they are unable to stand. Fortunately, for all this to happen a number of variables have to come together, and for the overwhelming majority of trees, this will never be an issue. So, they are free to keep on developing their roots in pursuit of the perfect rhizosphere

Black trees, black water and snow-covered roots. Walnut Creek by Jeffrey Hamilton on Unsplash.

Trees are our priceless companions on this planet. They are sources of life-giving oxygen, but also life-affirming joy and beauty. As we head into a new year, let’s all resolve to appreciate and protect them.

Stay warm and stay safe out there. 

Submitted by Pam

Snow falling on a white tree in a snow-covered field. There is a wooded hillside in the background.

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