Eli5 what governs the tree line? The cutoff with altitude is really clearly defined. Why? Is is the same altitude at all latitudes?

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Eli5 what governs the tree line? The cutoff with altitude is really clearly defined. Why? Is is the same altitude at all latitudes?

In: Biology

Because of air thinning. At around 12500 feet above sea level there is simply not enough air for the trees to thrive, so they don’t. You may find smaller shrub versions of trees in the transition, or ones that are less hungry for carbon dioxide like blueberry bushes.

Also carbon dioxide is heavier than most other components of air so it may literally fall out of thinned atmosphere, separately from oxygen and nitrogen. Which is how there is still (barely) enough oxygen for a human above the treeline for a few more thousand feet (before you have to bring canned air).

The tree line is determined by different limiting factors, above which trees can not survive. Usually it is cold temperatures or lack of water .

It’s a complicated series of factors including climate and species; [here’s a good writeup](https://www.nature.com/scitable/knowledge/library/global-treeline-position-15897370/), including a best fit chart of tree line altitude by latitude.

Edit to add the customary thanks for my first gold; I’ve never felt so much power!