1,000 trees is pretty much a drop in the bucket on a global scale, but every little bit helps.
Seriously. I think it would be safe to bet that I have over 1000 trees in my backyard alone (although the back 50 yards is forest). Now, they aren't all nice 2 feet in diameter beasts, they range from a couple inches in diameter (and a good 10 - 20 feet tall) to several feet in diameter (and a good 50 - 100 feet tall). We have enough trees in the US, we just need more trees in our urban areas.
For a very quick and dirty US tree population calculation:
The BLM (Burea of Land Management) manages 264 million acres of public land, approximately 1/8th the land area of the US. Most of this is just general land with a random array of forests, rivers, lakes, grassland, desert, chaparal etc.
Let's assume the average tree on BLM land is 8" in diameter
Let's assume the average distance between trees in 'dense forest' areas is 12'.
Let's assume that 'dense forest' land consists of 65% of the total BLM land.
One acre is 4.05e3 square meteres.
One square meter is 10.76 square feet.
One acre = 4.05e3 * 10.76 = 43,578 square feet.
For a square plot of dense forest, one side is SQRT(43578) = 208.753 ft in length.
Using the equation x * (8/12) + (x-1) * (12) = 208.753 where x is a number of trees, we can find the number of trees that will fit on one side of a square acre of 'dense forest'. We find that x = 17.428, the number of average trees that will fit on one side of our average square acre of 'dense forest'.
{Side Note: This number is slightly off because by the nature of this equation we are progressively adding fractional parts of the trees as we are adding fractional parts of the additional trees. So even though we could have half a tree on the edge of our acre, we do not have half a tree with this equation because when x = 1.5 (we are adding a tree and then another half a tree), the diameter added to the total number is 12" (1') and the distance between the trees added is 6' even though at 6' away from one tree we do not have half a tree yet (we have to go another 6' before we encounter the next tree). Still, this is just for approximation purposes.}
So, square that number to find the total number of trees on the average square acre of 'dense forest' 17.428^2 = 303.735 total trees.
Since we are assuming that 65% of the total land is 'dense forest' then .65 * 264 million = 171.6 million acres of 'dense forest'. Multiply that number by 303.735 trees per acre 171.6 million * 303.735 = 52.121 billion trees.
---
So, BLM manages 52.121 billion trees alone by itself. For simplistic purposes, let's assume that each tree produces 1 unit of oxygen in 1 year, so the BLM 'dense forest' land produces 52 121 000 000 units of oxygen in 1 year. If we add 1000 trees to the BLM population in 1 year, then the the BLM 'dense forest' land will produce 52 121 001 000 units of oxygen in 1 year.
That is a .0000192 % increase in oxygen unit production for the year. To increase the oxygen unit production for the year by 1 % based on the first year we started planting trees, we would need to plant 1000 trees per year for 521 210 year. Yes, half a million years later we will have effected the oxygen unit production by 1 %.
Obiously there are errors all over the place in the assumptions, etc of this calculation. However, I think if you accounted for every single piece of land in the US, or even take a look at the entire world, the statistics would look even worse, and you would need to exaggerate the number of years required to effect the oxygen unit product by 1 % immensely.
Edit: This does not mean that I am some anti-tree nazi, I personally love trees and feel sad for the thousands of people moving into these 'planned neighborhoods' around me where you might see some 1 inch diameter saplings every 50 feet along the sidewalk. I just think that we need to be planting millions of trees per year across the land in order to make the places we live that much more beautiful and friendly.

This poll was created on 2012-05-17 23:00:01
by KCAdmin