Life seems to grab hold wherever it can.
Deep sea vents, rocky cliffs, the underside of my window sill, everywhere except for the
tippy tops of mountains.
Why does nothing grow up there?
Hey everyone, Julia here for DNews.
The Tree line, is the elevation above which trees can’t grow.
From a distance the line can seem so extreme.
But up close it’s a little fuzzier.
Up close it’s more of a squiggly patch where flora grows thinner and thinner until no trees
grow in a place called the Alpine zone.
So some some scientists use the definition “the elevation where tree density declines
or drops to zero”.
But that elevation is different in lots of different places.
You might not be surprised to learn that there’s a relationship between treeline and latitude.
Treelines are pretty consistent between Between 30°N and 20°S. But the further you move
from that the lower the tree line is.
But within latitudes, it can differ a surprising amount.
Like for example, the treeline in the Eastern United States is lower than out West.
The Tetons in Wyoming are at 43 degrees latitude and the white mountains in New Hampshire are
at 44 degrees.
In the Tetons, the treeline sits at a chilly 10,000 feet.
While in the White Mountains it sits at a cozy over 4,500 feet.
What’s going on?
When we think of tree lines, we think of Alpine treelines in the mountains.
Researchers have found that treelines seem to follow the permanent snow line of mountains.
Which might mean temperature is the major factor.
And temperature really screws up two main things.
It limits how seeds sprout and limits how the tree grows.
If the elevation is too high, it’s too cold or if snow lasts too long into summer, trees
have a hard time growing.
It seems trees have a hard time building cells if the temperatures dip below 44 degrees Fahrenheit.
But SUMMER temperature matters a lot too.
If the snow lasts too long, it might cut the growing season short.
Leaving trees struggling.
Even on the same mountain it can vary!
Some rock faces get more sun, some get more rain, some more wind.
Ever been on a mountain and noticed how a slope on one side seems to have more trees?
Well shadows sometimes stunt tree growth.
In the Northern hemisphere north facing slopes have a lower treeline, because the shade makes
that side colder than the other!
It’s the opposite for the Southern Hemisphere.
But other factors matter too.
If the tree line is caused by wind, it might make the trees tiny, almost more like bushes.
These trees are called a krummholz formation, from the German word for 'twisted wood'.
Since temperature and treeline are linked, it’s no surprise that climate change has
an effect.
Treelines could almost be seen as a water mark for the warming world.
As the climate changes, treelines are moving.
So scientists are starting to keep an eye on treelines.
Just like stunning images of retreating glaciers, moving treelines might be a striking visual
for the way our world is transforming.
Alright guys, got any questions about how our weird world works?
Let us know in the comments below…