In a given area A, we have two choices - (i) we can plant maximum number of trees (which are larger in size) possible in A, say m OR (ii) we can plant maximum number of plants (which are smaller in size) possible in A, say n (evidently m will be smaller than n) Which choice will yield more amount of oxygen? It can be assumed that the total number of leaves capable of Photosynthesis is N and is same for both the cases.

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    $\begingroup$ The largest amount of Carbon-di-Oxide to Oxygen conversion in the world is done by single celled ocean phytoplankton (I think I saw in some documentary) $\endgroup$
    – One Face
    Feb 15 '15 at 17:15
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    $\begingroup$ Hard to plant them on land, though :-) $\endgroup$
    – jamesqf
    Feb 15 '15 at 18:00
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    $\begingroup$ I once read a study (but I don't remember the reference) that shows that you need a diversity of plants of different size to maximize the rate of oxygen production. I think, the rational behind this observation is that having a diversity of plant size increases the surface contact between leaves and air. $\endgroup$
    – Remi.b
    Feb 15 '15 at 18:08
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    $\begingroup$ Welcome to Biology S.E! If you need additional assistance, please visit The Help Center. This looks like it maybe a homework question; if it is then please show any work you have already done or what you think the answer may be. $\endgroup$
    – L.B.
    Feb 15 '15 at 19:21
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    $\begingroup$ @Remi.b It could also reduce intraspecific competition. $\endgroup$
    – canadianer
    Feb 15 '15 at 20:27

Ignoring parameters such as:

  • Leaf shapes
  • Difference in photosynthetic efficiency due to other metabolic factors
  • Unequal illumination of leaves
  • Nutrient content of the soil

Photosynthesis rate of a plant1 depends on the [total number of leaves] × [surface area of a leaf].

Assuming that a tree occupies same ground area as a shrub, there will be same number of trees as shrubs.

A tree is taller and can bear more number of leaves and if we assume that the surface area of the leaves are similar between trees and shrubs then the tree would carry out more photosynthesis.

However you say that the number of leaves is the same; in this case both will carry out same amount of photosynthesis (the shrub may outlive the tree though, as the latter won't be able to support its huge size with same level of photosynthesis as the shrub).

A note on phtoplanktons and algae: One reason amongst a few for why they are efficient at photosynthesis is because the number of photosynthetic cells per volume is higher in them.

1 I am using the term plant to denote all plants. Big trees are called trees and small plants are called shrubs, for convenience.


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