Don’t know why this has always bugged me, but once on a road trip my husband and I tried to “duke it out” over this one. Is there any way to know the approximate numbers?
I don’t know how accurate it is, but this site thinks it is trees.
From here:
http://www.worldchanging.com/local/seattle/archives/009087.html
I would guess Canada has more trees than the planet has people.
And the US also, by a very wide margin.
Of course it depends on how small a tree you are counting, but the number is enormous whatever you do. In Alaska alone, there are more that 600 billion trees on timber land greater than 1" in diameter and more than 300 billion greater than 3" in diameter. In the US, more than a billion trees are planted each year.
The US Forest Service has excellent information. Here is a good link:
The numbers above were taken from this spreadsheet:
These two numbers are clearly contradictory:
> Nadkarni used data from NASA satellites to estimate the number of trees at
> 400,246,300,201.
> In Alaska alone, there are more that 600 billion trees on timber land greater
> than 1" in diameter and more than 300 billion greater than 3" in diameter.
Also, why does the first statement give an exact number? Surely it’s impossible to estimate closer than to the nearest billion.
There are over 148 million square kilometers of land on Earth:
This website says that trees cover almost 30% of the land:
http://www.funtrivia.com/askft/Question96426.html
If both of those numbers are correct, there are almost 50 million square kilometers of forested land in the world. 400 billion trees would mean 8,000 trees per square kilometer. Since there are 1,000,000 square meters per kilometer, that would mean each tree gets about 125 square meters on average, which means each tree gets an 11 by 11 meter square. This strikes me as low. I would guess that at least five times that is closer. So I would guess that the true number is at least 2 trillion.
This is all back-of-the-envelope calculating. I KNOW THAT. I don’t need you to post to tell me how stupid I am. If you have better citations or better calculations, please give them. I’m doing the best I can with what numbers I can find offhand.
It’s quite tricky to define what counts as “a tree”, too. Do tiny saplings count? What about tall shrubs? Even counting only big adult trees, though, it seems pretty certain there are far more trees than people.
Just in the UK there are estimated to be 3.8 billion trees, which is more than half as many as the human population of the entire world.
Yeah, the first number seems to have a bit of a sig-fig problem. Either that or it’s no longer accurate because the city took out the two elm trees across the street. 
The way I thought about the question was in terms of population density. Consider Manila, with the highest population density on earth, which “only” has about 173 people per acre. Even out in my relatively arid part of the world that’s a pretty sparse forest-- I’m sure the big coastal forests and eastern forests are many times denser than that even. Sometimes they do drastic thinning on lodgepole pine forests in high fire risk areas, leaving something like 30 feet between trees. These are so sparse they just barely look like a forest on casual glace, but they’re still usually around 50 trees per acre which is denser than Manhattan. Considering that there’s only a few urban areas that come close to the density of a even the scraggliest of forests, I would also guess the tree-to-person ratio is much higher that the 61 the person came up with.
Heck, my garden has at least five times more trees (depending, again, on the definition of a tree) than there are people in my household, and I live in a small end-of-terrace suburban house.
Again that sort of depends on how big a sapling has to be before you call it a “tree”. Saplings can grow in very dense stands, especially around the edges of forests or wherever the canopy is disrupted. It’s not uncommon to find 1" diameter saplings growing at a density approaching one per square meter. Of course, at the other end of the scale, some forests aren’t nearly that dense. And I admit I have no idea how to average the two.
(Well, I suppose I do… ecologists often do transects where they count every plant on a small patch of forest. Do that often enough, and you can come up with average figures for every sort of forest. Then you just sum up the average density of a “forest type” multiplied by its total area. But I don’t have that data at hand…)
But even in the older-growth forests I’m familiar with, even where there are mostly a few large tree (1 per hundred sq meters?) there are still decent sized saplings sprinkled around.
Here are the numbers from the forest service for Alaska alone from the spreadsheet linked above (sorry about the formatting). The numbers for the US outside of Alaska add another ~50% to the total. Tree count is in thousands. The column headings represent the trunk diameter in inches. Again, the total for 1" and above is more that 600B. For the US as a whole it totals about 900 billion trees. The 400 B number for the whole earth is either nonsense, or is using a larger diameter cutoff.
Any back of the envelope calculation will tell you right away that there are more trees than people.
1-3 3-5 5-7 7-9 9-11 11-13 13+ Total
297,151 130,705 71,028 41,587 25,515 15,826 26,438 608,249
The number of 1" or greater trees per acre in the US excluding Alaska and Hawaii is 734. These numbers are for 2002 and are slightly higher than the numbers for 1977.
Searching for how many trees are cut down every year gives varying answers from 3 to 11 billion trees, roughly half to twice the human population of 6 billion. Even if we use the conservative figure of 3 billion cut down, for humans to outnumber trees would mean that we cut down half the trees on earth every year. That’s clearly not true.
Thanks for all the answers, everyone. And I am getting a huge kick out of this place! I am new to “StraightDope” and am thrilled to find a community of people that don’t just roll their eyes and ask “why does it matter?” to questions such as these. Of course, in this issue, the question of diameter is bound to come up, so in the argument between my hubby and me, I limited it to those an inch or thicker, as some of you did in your answers. And now, according to you all and your wise input, I am happy to say, I am the winner! Now I will go break it to him.