Tuesday, October 20, 2015

Forest Ecology Studies at Audubon Woods (16 OCT 2015)

Big-tooth Aspen leaf (October 2015)
Last Friday (16 October) I met with 3rd, 4th, and 5th grade students from Winn Elementary at the Chippewa Watershed Conservancy's Florence Maxwell Audubon Woods Preserve to continue an ongoing forest ecology study.  Students now come to the preserve twice a year (fall and spring) and perform a series of activities.  In the past, students have recorded sightings of plants and animals, collected leaves for preservation, and measured the Diameter - Breast Height (DBH) of trees.  In 2014 students counted the number of trees growing in 1/10 acre plots within the forest and used these numbers to estimate the total number of trees (with a diameter of greater than 1 inch) growing in the 40 acre preserve - their estimate between 24,000 and 29,000 trees!

Sassafras seedling at Audubon Woods Preserve

Counting Leaves

In June of 2015, the students were asked to calculate the number of leaves found on the forest floor.  They accomplished this by counting the leaves in 1 sq. ft. plots and using that data to estimate the number of leaves in one acre (43,560 sq. ft.), then multiplying that number by 40 to estimate the number of leaves on the entire forest floor.  Their estimates concluded that there were between 311,926,814 (low estimate) and 431,725,571 (high estimate) total leaves on the forest floor.

Winn Elementary students counting leaves in a square foot plot at Audubon Woods Preserve (October 2015)

Removing every single leaf from a plot

Last week the students repeated this experiment.  This time each group of students was asked to count three different one foot squares.  Here is the results from one of the three classes.

This class estimated that there were 248,519,148 leaves on the forest floor.  This number is significantly lower than the number from even the lowest estimate from June.  Many of the leaves that were present in June have since broken down and decomposed through the actions of invertebrates, fungi, and bacteria.

Fungi at Audubon Woods

Weighing Leaves
After determining the number of leaves on the forest floor, the next logical step was to try to determine the mass of all of those fallen leaves.  To perform this task, students collected 100 random leaves from the forest floor in a zip lock bag and then weighed them using a digital scale.  They then subtracted the weight of the bag and divided the result by 100 to determine the average mass of each leaf.  Measurements ranged from a low of 0.5888 grams/leaf to a high of 0.8888 grams per leaf.  These numbers were multiplied by the average estimate  of the number of leaves in the forest.  The resulting answer was then converted from grams to kilograms by dividing by 1,000.  Here are the results from one class.

Weighing leaves - Audubon Woods (October 2015)

They estimated that the total mass of the leaves on the forest floor was between 146,328.074 kilograms and 220,883.818 kilograms!  Converted to pounds, the leaves weigh between 322,598.18 and 486, 965.46 pounds!

Other Activities

Measuring canopy cover with a 10 x 10 grid

In addition to estimating both the number and weight of the leaves on the forest floor, students also examined canopy cover and measured the size of Sugar Maple leaves.   To measure canopy cover, one student lay on the ground and looked up at the sky through a 10 x 10 grid while another student recorded the grid squares that were covered by leaves.  They then had to answer the following questions:

       Do you think the amount of canopy cover will affect the types of wildflowers and other small
       plants that can grow in the forest?  Why or why not?

       Do you think the canopy cover can affect the amount of moisture in the soil?  Why or why not?

This job requires teamwork

Students measured the length and width of Sugar Maple leaves to determine an average leaf size.  After calculating an average size they had to explain why they think some leaves are larger than others.

Measuring Sugar Maple leaves

For some of the students this was their first trip to Audubon Woods.  For the 5th graders this was their fourth visit and they have been able to notice changes to the woods over the past two and a half years.  We already have a visit scheduled for late spring 2016.  Stay tuned for updates.

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