How trees hibernate
Now that the days are getting colder and we have had the first snow in the Netherlands, you could wonder when you receive your Treemore tree: how does this little tree survive the winter? In a previous blog we told you that some tree species such as Ginkgo, Birch and Albizia drop their leaves in the fall to withstand the cold winter. But dropping leaves isn't their only survival strategy. In this blog we tell you everything about the other ways in which trees protect themselves against the cold. From the natural antifreeze that trees create to how some species can even survive temperatures as low as -70 degrees Celsius!
Frozen Sugar Factories
First, trees have their own insulating material: bark. The covering of the trunk that gives trees their characteristic look is actually part of the dead bark. This layer offers a lot of protection against external influences, such as dehydration or infection, but also insulation against the cold [1].
The great danger in winter lies in freezing of the cells of the rest of the tree. These cells contain water and water – as we know from floating ice cubes – expands when it freezes. If water in the cells freezes, the cells can burst, causing them to die. Frost-resistant trees have come up with a solution: extracellular freezing. The moisture between the cells freezes sooner than the moisture in the cells. The moisture in the cells is gradually drawn out of the cells, so that the cell does not burst but shrinks [2].
Bevroren Suikerfabriekjes
Natural antifreeze
Unfortunately, this natural movement of the water causes another problem: dehydration. To avoid this, trees in the Northern Hemisphere have found several ways to survive long periods of frost. Sugars in the juice of the cells increase the viscosity and thus form a natural antifreeze. In this way, evergreen trees can remain green even at temperatures as low as -40.
For most of the world, this is enough winter protection, but it can be even more extreme. There are areas where the temperature drops below -60 degrees and still trees grow. The largest ice rabbit of all is the Asian larch. A conifer that loses its needles in the fall. It can tolerate temperatures below -70 and is the most northerly occurring tree in the world. For example, you can find it in Siberia at 72 latitude - way above the Arctic Circle at 66 latitude.
Trees of glass
The trees survive this extreme cold through vitrification. This is the chemical process we know best from making glass from sand, limestone, and soda. Glass is scientifically a liquid that hardly moves. That is why very old glass panes are thicker at the bottom than at the top: the glass slowly sinks down. In a tree, this chemical reaction results in a kind of suspended animation in which the molecules of the tree almost stop moving [3, 4]. Ice spreads by contact with other moving molecules, but if the molecules don't move, they don't react to each other [2].
Fortunately, we do not have such severe winters in the Netherlands and most of our baby trees can already stand outside in a larger pot. Please note: the roots can process much lower temperatures in a pot than in the open ground. And the roots are much less resistant to low temperatures than the above-ground parts. So at temperatures below -5 we recommend that you put the trees in a cool place in the house. This does not apply to the coffea arabica, which cannot tolerate a degree of frost. Look here for the care tips and frost resistance of all our trees.
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