Winter is Coming: Tree Edition

Photo credit: Alena Warren

Photo credit: Alena Warren

Far from the equator, organisms have found ways to tolerate the harsh changes that seasons bring.

The things that animals can do to tolerate winter are amazing and perhaps we can discuss those at a later time, because today I am interested in plants. Especially trees. Plants have to deal with the same challenges animals have in the winter: freezing temperatures, snow, and lack of food. Additionally, it seems like it should be even harder for plants because they can’t move around to try to address those challenges. Here are some of specific problems trees have with winter and the ways that they deal with them.

 

Ice

 

 

 

Challenge:

 

Water expands when it freezes. Trees have water in them. This is a problem because trees are made up of cells just like any other plant or animal, and if the water in the cell freezes and expands, the cell will likely burst. If the temperature fluctuates, freezing and thawing repeatedly can be especially troublesome for the tree.

 

 

Solutions:

 

Before winter, the tree relocates water from within the cells to between the cells [1]. This way, when it expands, it puts pressure on the shrunken cells and they are less likely to be damaged than if they were full of water.

 

The tree will also increase the amount of sugar in the water in and out of its cells, which reduces the freezing temperature of the water [1].

 

The characteristics of the tree bark may be a very useful winter adaptation for some tree species. Light-colored trees, like white and paper birch, reflect light better so that they are less likely to thaw on a warm winter day, reducing the danger of freeze-thaw cycles. Furrowed bark on other trees may help prevent splitting from freezing [1].

Reference: 

1. Northern Woodlands

Smooth bark. Photo credit: Alena Warren

Smooth bark. Photo credit: Alena Warren

Furrowed (thick, cracked) bark. Photo credit: Alena Warren

Furrowed (thick, cracked) bark. Photo credit: Alena Warren

Photo credit: Peter Warren

Photo credit: Peter Warren

 

Snow

 

 

 

Challenge:

 

Snow is heavy and sticky, and can cause a lot of damage by breaking tree branches.

 

 

Solutions:

 

Deciduous trees reduce the potential of damage from snow loads when they lose their leaves. There is less surface area for the snow to stay on. For this reason, snowstorms that occur before the leaves fall off can be more dangerous. Trees that have smooth bark are even better at shedding snow off before it builds up.

 

Evergreen trees like pines and hemlocks are in a different position: They keep their leaves through the winter, so they are more likely to collect snow. However, because their wood is less rigid, they are better able to bend under the snow and pop back up after it melts.

 

 

 

photo credit: Alena Warren

photo credit: Alena Warren

 

Food

Challenge:

Plants get food from the sun, which is at a lower angle in the winter and shining for a smaller fraction of the day.  

Solutions:

Shut it down. Photosynthesis makes food for the tree, but it also takes energy to perform it (you have to spend money to make money?), so sometimes it isn’t worth it. Different species have different thresholds for when photosynthesis is “worth it,” but winter in New England is too harsh for any of them.

Deciduous trees stop photosynthesizing when they drop their leaves (their photosynthesis factories). They store carbohydrates in their roots, and become dormant. It can be tough- the tree has to have enough energy stored to be able to regrow leaves in the spring before it can start making more food again.

Evergreens keep most of their leaves but they are otherwise not too different. Since they have leaves all year, they can take advantage of light that is available later in the fall and earlier in the spring than the deciduous trees.  On top of that, evergreens that find themselves under a deciduous tree are delighted when their competitor’s leaves fall off and they can bask in some uninterrupted sunlight for a short time. Ultimately, the freezing temperatures and lack of sun will cause photosynthesis to shut down in the evergreens as well.

I think it’s fascinating to learn about the ways that ecosystems adapt to harsh conditions. As a New Hampshire native, it doesn't seem harsh to me, but the temperature in this area can very from 0 to 100 degrees F in a given year, posing all sorts of challenges to the organisms not confined to climate-controlled buildings like I am. And yet, organisms survive and flourish here, and all over the Earth!

Thank you for reading! It's not winter yet, so get outside and see what the trees are doing!

 

Photo credit: Peter Warren

Photo credit: Peter Warren