Monday, October 18, 2010

Apple #488: How Many Leaves Fall

I've been walking around in the woods lately, enjoying the rustle and crackle of walking through fallen leaves on the paths and the leaves turning color on the trees.  This year's colors aren't quite as pyrotechnic as other years because it's been so dry, but some of the colors are still pretty eye-popping.

(Photos by the Apple Lady)

All these leaves turning and dropping to the ground led me to wonder, how many leaves fall each autumn?

Well, of course no one is going to go all across the country and count every single leaf on the ground.  Ho, ho, no, that would be silly (though I am wondering right now if it could be done, if you had enough people....).  So of course such a number has to be an estimate.

It turns out, even counting the number of trees is a near-impossibility.  But there are people at the US Forest Inventory & Analysis program who do count trees.  Or actually, they count a sample of trees within an area of forest and generate an estimate for the total number of trees in the entire forest.

And someone did come up with an estimate for the average number of leaves that grow on a mature tree:  about 200,000.

So, putting together all those estimates, I have a total estimate for you.  Drum-roll, please.

Or instead of a drum roll, how about a stroll across a leafy bridge?  If you want to count the leaves, or even the trees as you go, it would be much appreciated.
(Photo by the Apple Lady)

This number is for
  • In the United States only
  • not including Hawaii, New Mexico, West Texas, or Wyoming
  • forest land only (not counting the trees in your yard or the local city park or along your streets, etc.)
  • does not include timberland either (land owned by industrial companies)
  • hardwood trees only (the best way to get deciduous trees only, and no conifers)
  • doesn't include every single variety of hardwood in existence, but includes the major and most common species
  • only those hardwoods that measure 1" in diameter at breast height (dbh)

Estimated number of trees that drop their leaves in the forests of the US: 203,257,948,035.  (Over 203 billion, in other words)

Multiply that number of trees by 200,000 leaves, and you get, depending on your preferred method of notation:
  • 40,651,600,000,000,000
  • or 4.06516 E+16
  • or more than 40 quadrillion leaves.
Given all the bits & pieces of data (trees) that are not included, I'd say that's probably a third of the actual total.

These leaves strewn all across this path are only a very small sample of the 40 -- or perhaps 120 -- quadrillion leaves that will fall this autumn.
(Photo by the Apple Lady)

USDA Forest Service, Forest Inventory & Analysis, Forest Inventory Data Online, Standard Reports
Wisconsin County Forests, Questions and Answers about Wisconsin Forests

1 comment:

  1. As a college student, in my environmental field studies class, we once had to calculate the mass of wood in an acre of forest near the school by measuring one tree and averaging. Needless to say we were not very close.


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