Silent Survivors: The Winter Life of Trees

- Hi, Sanford Smith here from Penn State Cooperative Extension.

Today, I'm out in the forest, in the winter, and I'm gonna talk about some of the different enemies that trees have.

Now, trees have things like insects and diseases and wildlife and fungi that attack them.

And sometimes people impact trees as well.

But in the winter, trees suffer a whole new set of challenges and they have to adapt and use strategies to get through the winter every year.

It's a real challenge for trees.

So while there are many different things I could talk about, I'm gonna talk about two main areas, and one is how trees manage water, and also how trees manage food production.

In other words making sugar.

Trees pump or suck up a lot of water all through the year when they have their leaves on, because the leaves create this sort of suction to bring water from the roots up to the leaves to do photosynthesis in their leaves.

When it comes time to drop their leaves in the fall, because the days are getting shorter and it's getting colder, they stop that pumping up or sucking up of the water and go into sort of a dormant mode in regards to water.

But trees also have to deal with the water that's still in them.

And there's several different tactics they use.

And one is to move water out of their cells to the intercellular areas, or the areas that are not within living cells.

Sometimes it's into the dead wood or into the vessels of the wood.

And they do this by creating a protein in the living cell called a ice nucleator.

And that's drawn out of the living cell into those inner cellular non-living areas.

And that causes water then to move out of the cells, too, and then form ice crystals on the outside of the cell.

So these nucleators, which are sort of mimicking an ice crystal themselves, draw the water out of the living cells and then provide a place for ice crystals to form outside of the living cells.

So those ice crystals don't damage the living cells.

Another interesting thing is that trees produce other proteins that are like anti-freezes as well.

So that can keep the tree from freezing in its internal living tissues.

The sugars that are left inside of the living cells are more concentrated, too, when water is pulled out of them.

And those act like anti-freezes, too, they lower the freezing point inside that cell and keeps it from freezing in the winter.

So there trees are actually saying we're gonna just have freezing in this area and it's a kind of a non-living area and it prevents damage to the trees.

Now, interestingly, there are some other animals in nature that do this very same thing, and those are the hibernating frogs.

Frogs will freeze portions of their body that are non-living and also use anti-freeze to prevent the living tissues from freezing.

Many plants will do this, that over winter perennial plants, as well as animals.

So it's just sort of a fascinating thing that frogs stay partially frozen like trees do and they use anti-freeze to keep their living tissues alive and unharmed.

The last thing I wanna talk about is how trees keep making sugar.

So most of us know that leaves on trees are going to be where the sugar is produced in the tree, and then that produces energy for the tree.

They burn that when they respire, when trees are growing and functioning.

Lots of times people think that, well, a pine tree such as this, can still photosynthesize in the winter and they're right, they can.

When temperatures go about 45 degrees or up, this can warm and these needles can photosynthesize.

But the larger trees they've lost their leaves where they're doing carrying out photosynthesis, but they have some other tricks.

Now, one species of tree, the Quaking Aspen, will have quite a bit of chlorophyll under its bark.

And the chlorophyll is where the photosynthesis is occurring.

And so when the sun hits the bark on the tree and if it warms it up, it's going to photosynthesize there.

And then I'm going to reach over here and grab a branch here from a hardwood tree, which is a deciduous tree, like this Red Oak here.

Interestingly enough, there's quite a bit of photosynthesis that goes on in the small twigs, and you can scratch this off out here and see green photosynthetic material, or chlorophyll under the bark.

So this is also producing some sugar for the tree as well.

So these have been a few thoughts about the way trees survive the winter.

They're sort of the silent survivors out here, very quietly going about their business of freezing certain areas and using a little antifreeze in their pipes, so to speak, and also producing sugar.