The Bark Biters: What Affects Leaf Fall

This topic submitted by Angela L., John P., Heather A., Kelly F., Terry M. ( ) on 12/12/98 .

The Bark Biters
Angela Levinsky,
Terry McCormick,
Jon Peake,
Kelly Frendt,
Heather Ashdown
Natural Systems
Olivia Campbell

What Affects Leaf Fall


1. Question: "What are the environmental and/or non-environmental elements that affect the falling of deciduous leaves?" The reason that we chose to pursue this question is mainly because of the inherent environment that surrounds us. It is Autumn and the trees in Oxford are starting to go through many seasonal changes that can be observed both scientifically and visually. We feel that certain environmental issues such as weather and soil can be addressed.

2. Purpose: To look more in depth into the falling leaves which most
people take for granted. We feel that there are many elements that affect leaf fall. Our hypothesis is as follows: Wind, rain, temperature,barometric pressure, and acidity In the soil all influence leaf fall.

3. Reasons behind project: We chose to do this lab experiment because it relates strongly to our current environment . Oxford offers an exemplary cross section of deciduous trees to which we can apply to our lab. Also, our time frame for observations matches perfectly with the fall season.

4. Accomplishments: To create sound explanations of how and why leaves fall in Autumn.

5. Relevance: We feel that our results can benefit all people and provide a thorough explanation of leaf fall that is easy to understand.

Literature Review:
"Some three hundred years ago, J. B. Van Helmont (1577-1644), made an attempt to find out what trees were really made of. He also wanted to find out if Aristotle’s idea that trees derive their food from the earth was correct. To do this he performed an experiment in which he planted a willow tree in a tub with earth and accurately weighed both the tree and the soil. For five years he added nothing but water to the tub. Then he carefully removed the willow, complete with all its roots, from the tub and weighted both the tree and the soil. To his surprise, he found that the weight of the soil had decreased only two ounces, although the tree, not counting five years of shed leaves, had added more than 164 pounds to its original weight. Van Helmont rightly concluded that only a minute amount of the substance of the tree had come from the soil, while the major part must have been supplied by water and air" (Feinlnger).
Von Helmonts experiment answers only one component of our experiment. From this we can conclude that soil itself does not enter the tree, so there must be something in the soil that aids the tree in its growth throughout life. In finding what affects leaf fall we observed a number of variables, some of which came from the soil. It has been noted that top soil, "the most precious substance," contains large quantities of water and air . This topsoil is also alive with biological activity and contains nutrients for healthy growth such as nitrate and phosphate (Feinlnger). We want to take Helmonts experiment a step futher and find out whether or not the nutrients in the soil influence the rate at which leaves fall.
Hopefully this project will bring about a greater understanding of the affects that cause leaves to fall.

- string and golf tees -- Used to mark out three foot squares under each tree.
- Nitrate, Phosphorous and pH Kits (glass tubes included) – Used to measure the Nitrate, Phosphorous and pH levels in the soil.
- (2) 100ml beakers
- 50ml of water
- 1 gram of soil per square per week
- pH Testing kit
- Nitrate testing solution
- Phosphorous testing solution
- Filter Paper
- Plastic Dropper
- Glass Tubes
- Weather reports -- Used to obtain climate observations, temperature, wind and barometric readings.
- Computer programs -- Used to organize and analyze our data.
- Peer Science center and Olivia Campbell -- Many of our questions were answered by these people. And if our questions were not answered they directed us to informational sources in which we could obtain the information needed.

In determining what affects leaf fall, we took many factors into account. We wanted to concentrate our observations on only a couple types of trees. In doing so we had to determine which trees were dominant in this area. We walked through Western and collected leaves. We focused our lab on trees that appeared most frequently. We took these leaves, studied them closely and then used the book Manual of Trees of North America to determined the species of trees that we had found. This led us to take our tree samples from Maple and Locust trees.
After figuring this out, we thought about what things might affect the rate at which leaves falls. We considered nutrients in the soil such as phosphorous and nitrate, the pH of the soil, wind, temperature, barometer readings, rain, sun and clouds. We observed the color of the leaves and the amount that fell each day. Our test groups were two three foot squares, one near the tree and one further away from the tree, marked off with string and golf tees. All our measurements concerning leaves and soil came from these squares.
Every day for about a month we counted the amount of leaves in these squares. We also noted the color of the leaves as they fell and the progression of color change on the trees as the month progressed. Soil samples were taken from both squares under each tree once a week. These samples were later tested for Ph, Phosphorous and nitrate levels (see student procedure for directions on how to conduct these tests). While most of our group was off taking measurements on the trees, one member kept close track of the weather day by day. Each day the wind, climate, temperature and barometric pressure were recorded. After we had collected all of our data, we then sat down to compare all the information we had obtained.

Class Participation:
Materials that class will be using (per group):
- 2 100ml beakers
- 50ml of water for each soil test
- 1 gram of each soil sample
- filter paper
- pH testing solution
- Nitrate tester solution
- Phosphorous tester solution
- plastic dropper
- Glass tubes

Student Procedure:
Students will conduct the lab experiment in their lab groups. Each group will be given two weeks worth of soil from the same tree. They will then be asked to find the pH, phosphorous and nitrate levels in the soil. With this information they then will be asked to compare and contrast the differences in content, if there is any, of the soil. Each group will also be given other information such as wind, climate, temperature, barometric pressure, the amount of leaves that fell each day, and the color of the leaves (obtained the day of the lab). From this data and the data that they concluded they will be asked to draw conclusions on what they believe affects leaf fall. Each group will also be asked to fill out student questions concerning both the lab experiment and how we conducted this lab.

Step One
For all tests a water solution of the soil must be made. To do this students will need to measure out a gram of soil and mix it with 50ml of water for five minutes. After doing this students will need to use a filter to remove excess particles from the water. This "solution" will be used for the rest of the tests.

pH Test
1. Take the pH testing tube and fill to the line with the water solution that you made above.
2. Add 10 drops of the pH Testing solution.
3. Agitate
4. To determine pH, compare to the pH color chart.
5. Record data.

Phosphorous Test
Step 1: Fill tube to the first line with water solution.
Step 2: Add 6 drops of phosphorous rgt 2, cap and shake to mix
Step 3: Add one phosphorous rgt 3 tablet, cap and shake until dissolved
Step 4: Compare color against phosphorous color chart
Step 5: Record data.

Nitrate Test
Step 1: Fill tube to first line with prepared water solution.
Step 2: Add packet of 6 Nitrate Regent and shake well.
Step 3: Add packet of 3 Nitrate Regent and shake well.
Step 4: Compare to Nitrate color wheel. It will take about three minutes for the color to appear
Step 5: Record Data

Tree Name: Bert
Tree Type: Locust
Monitor: Angela

date Amt. Leaf color Temp. Humid. Wind Barom
10/12 12 6 yellow 70 deg 30% 13mph 30.02
10/13 9 13 yellow 51 deg 48% 4mph 30.31
10/14 15 10 yellow
10/15 8 10 yellow
10/16 10 7 yellow
10/17 6 5 yellow
10/18 11 14 yellow
10/19 15 13 yellow
10/20 12 18 yellow
10/21 17 20 yell/bro
10/22 15 22 yell/bro 58 deg 44% 4mph 30.30
10/23 18 25 yell/bro 68 deg 33% 6mph 30.34
10/24 20 30 yell/bro 68 deg 41% 3mph 30.26
10/25 30 27 yell/bro 72 deg 38% 7mph 30.19
10/26 27 25 yell/bro
10/27 29 30 yell/bro 64 deg 84% 3mph 29.96
10/28 37 51 yell/bro
10/29 42 35 yell/bro
10/30 49 61 brown
10/31 59 46 brown
11/1 62 71 brown
11/2 50 64 brown 49 deg 89% 5mph 29.99
11/3 65 67 brown 47 deg 93% 6mph 29.98
11/4 53 62 brown 45 deg 85% 10mph 30.12
11/5 61 55 brown
11/6 66 69 brown
11/7 65 72 brown
11/8 75 68 brown 48 deg 71% 6mph 30.20
11/9 73 64 brown

Tree Name: Earnie
Tree Type: Locust
Monitor: Terry

date Amt. Leafs color Temp. Humid. Wind Barom
10/12 84 32 green 70 deg 30% 13mph 30.02
10/13 61 41 green 51 deg 48% 4mph 30.31
10/14 71 45 green
10/15 67 52 green
10/16 70 41 green
10/17 75 36 green
10/18 63 42 green
10/19 31 53 green
10/20 54 42 green
10/21 22 31 green
10/22 62 20 green 58 deg 44% 4mph 30.30
10/23 77 29 green 68 deg 33% 6mph 30.34
10/24 83 77 green 68 deg 41% 3mph 30.26
10/25 71 93 green 72 deg 38% 7mph 30.19
10/26 90 57 green
10/27 84 49 gre/yel 64 deg 84% 3mph 29.96
10/28 79 83 gre/yel
10/29 88 71 gre/yel
10/30 107 57 gre/yel
10/31 94 113 gre/yel
11/1 193 111 yellow
11/2 320 295 yellow 49 deg 89% 5mph 29.99
11/3 52 30 yellow 47 deg 93% 6mph 29.98
11/4 67 25 yellow 45 deg 85% 10mph 30.12
11/5 60 42 yellow
11/6 53 27 yellow
11/7 16 10 bro/yel
11/8 24 30 bro/yel 48 deg 71% 6mph 30.20
11/9 31 9 bro/yel

Tree Name: Grover
Tree Type: Maple
Monitor: Heather

date Amt. Leafs color Temp. Humid. Wind Barom
10/12 0 2 brown 70 deg 30% 13mph 30.02
10/13 1 1 red/gre 51 deg 48% 4mph 30.31
10/14 0 0 red/gre
10/15 0 0 red/gre
10/16 0 0 yellow
10/17 4 2 yell/bro
10/18 5 6 yell/bro
10/22 58 deg 44% 4mph 30.30
10/23 77 73 yell/red68 deg 33% 6mph 30.34
10/24 15 2 bro/red 68 deg 41% 3mph 30.26
10/25 57 15 bro/red 72 deg 38% 7mph 30.19
10/26 42 12 Y/O/R
10/27 70 29 yell/red64 deg 84% 3mph 29.96
10/28 49 42 red/bro
10/29 66 50 red/bro
10/30 71 50 R/B/O
10/31 498 370 R/B/O
11/1 156 70 Y/R/O
11/2 146 51 Y/R/O 49 deg 89% 5mph 29.99
11/3 164 85 Y/R/O 47 deg 93% 6mph 29.98
11/4 20 20 Y/R/O 45 deg 85% 10mph 30.12
11/5 10 13 Y/R/O
11/6 4 8 Y/R/O
11/7 5 9 Y/R/O
11/8 3 2 Y/R/O 48 deg 71% 6mph 30.20
11/9 4 0 Y/R/O

Tree Name: Oscar
Tree Type: Maple
Monitor: Kelly

date Amt. Leafs color Temp. Humid. Wind Barom
10/12 19 16 brown 70 deg 30% 13mph 30.02
10/13 3 2 brown 51 deg 48% 4mph 30.31
10/14 5 1 brown
10/15 4 2 brown
10/16 2 1 brown
10/17 1 2 brown
10/18 5 3 brown
10/19 5 4 brown
10/20 3 2 yell/org
10/21 3 3 yell/org
10/22 2 1 yell/org 58 deg 44% 4mph 30.30
10/23 3 2 yell/org 68 deg 33% 6mph 30.34
10/24 4 3 yell/red 68 deg 41% 3mph 30.26
10/25 4 3 yell/red 72 deg 38% 7mph 30.19
10/26 6 9 org/red
10/27 8 11 org/red 64 deg 84% 3mph 29.96
10/28 13 13 org/red
10/29 11 7 orange
10/30 15 25 orange
10/31 23 6 orange
11/1 42 37 orange
11/2 240 215 orange 49 deg 89% 5mph 29.99
11/3 38 46 orange 47 deg 93% 6mph 29.98
11/4 150 125 orange 45 deg 85% 10mph 30.12
11/5 111 120 orange
11/6 20 90 orange
11/7 11 13 orange
11/8 7 8 orange 48 deg 71% 6mph 30.20
11/9 5 9 orange

Tree Name: Bert
Type of Tree: Locust
week Ph Nitrate Phosphorous
1 Close 8.5 1 50mg/l
1 Far 8.5 1.2 50mg/l
2 Close 8.5 1.4 50mg/l
2 Far 8.5 .8 50mg/l
3 Close 8.5 .9 50mg/l
3 Far 8.5 .8 50mg/l
4 Close 8 1.7 50mg/l
4 Far 8 1.0 50mg/l

Tree Name: Earnie
Type of Tree: Locust
week Ph Nitrate Phosphorous
1 Close 7.7 3.0 43mg/l
1 Far 9.0 1.0 50mg/l
2 Close 6.8 1.8 40mg/l
2 Far 8.5 2.0 45mg/l
3 Close 7.7 1.0 50mg/l
3 Far 8.2 2.1 50mg/l
4 Close 8 2.0 45mg/l
4 Far 8.5 1.7 50mg/l

Tree Name: Grover
Type of Tree: Locust
week Ph Nitrate Phosphorous
1 Close 8.5 .8 50mg/l
1 Far 8.5 2.0 49mg/l
2 Close 8 2.0 50mg/l
2 Far 8 1.8 50mg/l
3 Close 8.5 .9 45mg/l
3 Far 8 1.0 50mg/l
4 Close 8 .9 49.7mg/l
4 Far 8 1.0 50mg/l

Tree Name: Oscar
Type of Tree: Locust
week Ph Nitrate Phosphorous
1 Close 9 1.0 50mg/l
1 Far 8.5 .6 50mg/l
2 Close 9 .4 50mg/l
2 Far 9 .7 50mg/l
3 Close 7.5 .9 50mg/l
3 Far 8.5 .7 50mg/l
4 Close 8 1.0 50mg/l
4 Far 8 2.0 50mg/l

Analysis of Results:

All the trees followed pretty much the same trend. They started off losing a relatively low amount of leaves to losing high numbers of leaves, then back to a lesser amount, producing a bell shaped curve effect on our graphs. Between the 30th of October and the 5th of November large amounts of leaves fell from our trees. We yield this to increases in storms and wind, and deficiency of sunlight. pH was relatively consistent. Yielding basic to neutral readings. The Nitrate tests indicated to us that there were active levels of nitrate in the soil throughout the duration of our observations. The phosphorous test also indicated to us that there were highly active levels in the soil.


Restate Question : What are the environmental and or non-environmental elements that affect the falling of deciduous leaves.

Restate Hypothesis: Wind, Rain, Temperature, barometric pressure and elements in the soil all influence leaf fall.

From our data and our results we can conclude that the environment does affect the falling of deciduous leaves. The temperature, elements in the soil and the weather (sunlight, wind, and rain), as noted in the results, play a key factor as to when leaves fall. When the temperature and sunlight decreases and rain and wind increase the falling of deciduous leaves increases. The elements in the soil affect the falling of leaves through a process called photosynthesis where the elements in the soil, in our case nitrate and phosphorus, aid in this process. In the fall and winter season plants stop this food making process. The Chlorophyll goes away and the leaves change color because of this. These colors were always there, they were just covered up by the green produced by the chlorophyll.
From our research we have found that during the winter months when the leaves begin to fall that the days become shorter, the temperature decreases, that there is a decreases in sunlight intensity, there are shorter hours in the day. All these processes reduce the food making process. The shorter days also cause hormone changes in the trees. Materials from the environment are then called back into the leaves to aid in these hormone changes.

Student Questions

1a. What do you think is the biggest factor in the rate in which leaves fall?

A. Amount of water in the ground.
B. Outside conditions: Wind, rain, harsh weather.
C. wind
D. Temperature

1b. Why?

A. Water is part of chlorophyll, which strengthens leaves and keeps them attached.
B. Blows them off before they fall naturally.
C. Constant agitation of the leaves - like wiggling a tooth.
D. When it gets colder, the food is not able to make it to the stems/branches, therefore the leaves are cut off from their food supply. They eventually change color and fall off.

2a. Do you suppose that wind and the direction that it is blowing should be taken into consideration in the position of our 3x3 squares? Why?

A. Yes. if winds blow from the west and you put them on the west side you will not collect the leaves.
B. No. Wind is so random, it is difficult to apply.
C. wind definitely should be considered. Direction? Probably not.
D. No because the wind direction will switch directions so much, that the difference will be accounted for by taking the average of all directions.

3. Do you think that the temperature "talks" to the leaves and therefore determines when and how many leaves fall?

A. Yes
B. To a point - but results are constant due to different spaces.
C. Yes.
D. Yes, see answer #1

4. Knowing the effect that humidity has on people and the fluids in our bodies, what can you conclude about the affects of humidity as the trees shed their leaves.

A. Humidity makes them shed, as we sweat.
B. Large levels of water causes photosynthesis to stop.
C. Humidity increases - less leaves falling. Vice versa.
D. The more humid it is the more color the leaves have.

5a. How do you think sun rise and sun set affect the time of year the leaves fall.

A. The amount of sunlight for the chlorophyll.
B. Less sunlight during the winter season causes less photosynthesis to occur.
C. Not sure how, but the shorter days are in the fall when the leaves fall not in the spring, thus it definately must play a part.
D. What does that have to do with it? Less humidity in the winter?

5b. Why don’t the leaves change color and fall in the spring?

A. It gets warmer so that they grow in.
B. In the spring there is an decrease level of water/sunlight promoting photosynthesis.
C. Temperature, daylight.
D. Because its warming up in the spring, not cooling down. And cold produces leaf fall.

Reading Information:
These excerpts are ones that we found on the Internet. They give us, in some detail, an explanation to why leaves change color and fall during the autumn season. These excerpts may also be taken into consideration when comparing and contrasting our data.
From the web site:

Plants make their own food in the summer. They use water, a gas from the air called carbon dioxide, and sunlight. They get help from something called chlorophyll. The chlorophyll gives leaves their green color
Winter days are short and dry. Plants stop making food. In some leaves, the chlorophyll goes away in the fall. Then we see orange and yellow colors. These colors were there all summer, but the green covered them up.
Some leaves turn red. This color is made only in the fall, from food trapped in the leaves. Brown colors are also made in the fall. They come from wastes left in the leaves.

From the web site:


As the fall season marches on, the days become shorter. The decrease in sunlight intensity, shorter hours, and cooler temperatures reduce the growth and food-making processes that normally flourish during the spring and summer seasons.
Plants rely on sunlight for energy and nutrients. Each leaf contains chlorophyll, which absorbs sunlight energy to make sugar and carbohydrates (food for the plant) with CO2 and water through a process called photosynthesis.
A couple of weeks before the leaves change color, a hardened cell layer forms at the base of the leaf due to the decreased photosynthesis. This layer blocks nutrients and moisture flow to the leaf, inhibiting further production of chlorophyll.
The chlorophyll begins to break down as the tree absorbs the nutrients into the trunk and eventually, the roots. As this occurs, green color starts to diminish since chlorophyll reflects green wavelengths. The yellow, red and orange pigments existed in the leaf since spring but were not visible until this point because of the large amounts of chlorophyll.


xCO2 + yH2O à xO2 + C(H2O)y

Works Cited

Sargent, Charles Sprangue. Manual of trees of North America. Dover Publications, inc.. New York: 1965.

Feinlnger, Andreas. Trees. The Viking Press. New York: 1968.

Bell, C. Ritchie. Lindsey, Anne H.. Fall Color. Laural Hill Press. Chapel Hill,North Carolina: 1990.

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