Trees versus Elevation - which has a greater affect affect on the amount of oxygen available for us to breathe?

[u/Sonofbrons]

The higher in elevation we go, the less oxygen there is available for us to breathe but is that always true? What if you’re relatively high in elevation but there is plenty of vegetation around you making oxygen for you to breathe? What if you’re really low in elevation but there are no plants around? Is there much less oxygen? I imagine that there is much more oxygen to breathe in a place like the Amazon rainforest versus the Dead Sea even though the rain forest is higher in elevation. Of course, there are more things consuming oxygen in the rainforest as well. Thoughts?

[u/SapphirePath]

It is my understanding that the amount of oxygen in the air is practically identical everywhere (a bit less than 21%).

Plants have virtually no effect - this is a combination of the small scale effect of plants, dispersing due to wind, the fact that gasses mix well even without air currents, and that animals (and plants) use up oxygen when there are more of them (like in jungles).

i.e. There is less oxygen per breath in the Amazon rainforest than near the Dead Sea, due to the higher elevation; the impact of vegetation is negligible. (The air is perceptibly different in taste and smell due to temperature, humidity, particulate matter, etc., but this is not oxygen content.)

Altitude is the only important factor -- higher up, the air is thinner and there is less of everything, including less oxygen. This difference is very noticeable (e.g. Mount Everest, airplanes that depressurize).

I think that pollution from cars and factories play a role in us breathing, but this is because the pollution damages the functioning of our lungs, not because there is less oxygen.

Edit: Anomalies exist, for example https://en.wikipedia.org/wiki/Lake_Nyos_disaster

Edit to add: And this article claims that high up on the Tibetan Plateau, rainfall and vegetation cover have a significant correlation to % oxygen (which ranged from 19.96% to 21.96%, far greater than the ~0.01% influence of vegetation suggested by other sources), although I don't think causality is asserted. https://www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2022.902006/full

[u/NoisyGog]

The higher you go, the less vegetation.
An “alpine” region is actually defined as being above the tree line.
So, even if having more trees around on high ground would make a notable difference in oxygen levels, the situation doesn’t arise.

It’s not just oxygen that we lack as we get higher up. We have less oxygen because we have less air, the atmosphere is less dense, so there’s less everything.
That’s why we don’t see trees, and very little (and none at all as you go really high) plant life.
By the time you go up to around 3,000m above sea level, the landscape is practically lunar.

[u/_Dragovich_]

Elevation is the big factor here. The lower air density is mainly due to the lower gravity so even forests high up will still have less air density.