I know this is crude, but I am really curious as to how these things are measured so here goes:

 

How many trees would one person need in a year to have enough oxygen to live?

 

That is: Picture a very basic version of Biosphere 2, all complete except there is no oxygen / no oxygen source. Pretend Biosphere 2 is only 10 sq m big.

What is the MINIMUM number of plants one person would need to have enough oxygen for a year?

 

- or what is the volume of oxygen an individual consumes per year, and what is the volume of plants that could supply this oxygen?

 

Wait a minute...how would the bodies of water form in Biosphere 2 the first place....

 

Im sure somebody out there can sort this out.......

NASA astronauts consume an average of 0.84kg of oxygen per day, so that's 307kg per year. How much trees produce is harder to find, as I guess it depends on the type of tree. I searched for answers and got a huge range of figures, from "a mature leafy tree" providing enough O2 for 10 people, to 22 trees (type unspecified) needed per person, or 18 people per acre of "forest."

 

In any case, if all you need is oxygen, I expect you'd be better off with algae, which can reproduce like crazy and is "all leaf."