[Geof]

I have seen this claim before but like in this thread I have not seen it backed up with a reference to the original source and how the data was collected for the comparison. It could be simply an Urban Myth but I haven't looked for it on Mythbusters.

But having said that there is a way it could be possible.

I have seen pictures from the beginning of the 1900's showing Ponderosa Pine forests and then pictures in the same region taken 80 or 90 years later. The difference was dramatic with a much denser tree cover in the later pictures; I seem to remember it was stated that in the early forest the average distance between trees was something like 10 meters but the recent forest had a spacing of 3 meters. This is a result of fire management; trees and forests over just about the whole of the North American continent are adapted to exist with fairly frequent low intensity forest fires, the trees can survive a little scorching. These fires naturally thin the trees out because if there happens to be a stand of trees that are closely spaced the fire is hotter and some of the trees get scorched too much and die.

The closer spacing results in about three times as many trees in the same area so even though there is less treed area across the continent there could be more trees.

But it is irrelevant to Global Warming and human released CO2. Do a calculation and figure out how many barrels of oil a tree is equivalent to; especially a scrawny Ponderosa Pine. On a dry weight basis wood contains about as much Carbon as the same weight of gasoline; the about is plus or minus say 50%, I am not talking high precision here. So you can figure out how much weight the trees in your backyard need to put on each year to compensate for the petroleum products you have used in the same year. You will need a very big backyard with a lot of trees but most important you are not allowed to let them die and rot away...ever! Because if they do then the CO2 is back in the atmosphere again.