Counting Leaves On the Forest Floor

Have you ever walked into a forest and wondered how many leaves were on the forest floor?

I have.

Yesterday, I gave three classrooms from Winn Elementary the task of finding out.

It sounds like a daunting task at first, until you break it down.  The students were visiting the Chippewa Watershed Conservancy's Audubon Woods Preserve for a forest ecology activity.  Audubon Woods Preserve is approximately 40 acres in size.  For those that don't know, an acre of land is 43,560 square feet - if you think of an acre as a square each side of the square would be about 208 feet long.  So at 43,560 sq. feet per acre times 40 acres, Audubon Woods equals 1,742,400 sq. feet!

Even if the number of leaves in one square foot took only 3 minutes to count (on average) it would take one person 5,227,200 minutes to count all of the leaves in the forest.  That is 87,120 hours or 3630 days or just 20 days short of 10 years.  During those ten years some leaves would decay and others would be added every year so it would be impossible to get an accurate count.

Instead of trying to count every single leaf, what if you count the leaves in individual random sections measuring 1 square foot and use those counts to find an average?  This solution is much less time consuming and will give you a reasonable estimate of the number of leaves.

The students were provided with a one foot square made of PVC pipe and the following worksheet and set to work.

Beginning the counting process on a randomly chosen square foot plot

Students took great care to make sure that they counted every single leaf in their plot

A students with a large handful of leaves that she has counted.

An empty one foot square after all of the leaves have been removed and counted - the leaves were then put back in place

Because the squares were tossed into the forest randomly and in widely separated spots in the forest, the number of leaves in each square varied greatly.  Here are the results from one student group.

This group of students was in one of the sections of forest with denser patches of leaves and their large count (305 leaves) reflects that.  One group in the same class had less than half the number of leaves in their square.  Overall this class came up with an average estimate of 431,725,571 leaves in the 40 acre forest!  This translates to 10,793,139 leaves per acre or approximately 248 leavers per sq. foot of the forest floor.

The other classes came up with estimates of 347,733,268 total leaves (8,693,332 leaves per acre or roughly 200 leaves per sq. foot) and 311,926,814 total leaves (7,798,170 leaves per acre or 179 leaves per sq. foot).

Calculating an average of the 21 test plots used over the course of the day we came up with an average of 363,795,218 fallen leaves on the floor of Audubon Woods.  This translates to 9,094,880 leaves per acre of forest floor or just under 209 leaves per every square foot of the forest floor.