What Effects Do Trees Have On The Environment?

Introduction
The environment affects trees, but trees can also affect the environment. A tree needs water, minerals, carbon dioxide, and sunlight. The pH, moisture content, type of soil, competition, and mankind all affect tree growth. This experiment is designed to help us understand how trees affect the environment around them.

Many other factors are now being investigated for trees the same way that they are for people. The forest is much different than an urban area. While taking measurements of these environmental factors, consider what other factors you could measure. Which of these factors do you think are important to a homeowner / forester?

Question

  1. Does the soil moisture, soil pH, soil temperature and humidity vary from tree to tree?

Hypothesis
     Students are to write their own before continuing.

Materials
Air thermometer Soil thermometer
Sling psychrometer pH meter/pH paper
Moisture meter Meter sticks
15 cm rulers Plastic bags

Possible option:
    Balances / scales
    Distilled water

Procedure

  1. Students will work in groups to prepare the appropriate data tables.
  2. Take the first set of air and soil temperatures at the base (bole) of the tree, and the second set at the drip line (measure the distance from the trunk). The final set should be taken at least 5 meters from the tree in full sun.
  3. The pH should be measured using the pH meter at the same distances as the temperatures. If pH is to be tested, collect a soil sample, place in a plastic bag, and return it to the laboratory. In the lab, add an equal amount of distilled water to the soil sample, and then in three to five minutes (when the soil has settled) use the pH paper.
  4. Measure the soil moisture with the meter at the same locations.
  5. Measure the humidity in the same approximate locations.

Results
The data for your group's work should be checked with the teacher before it is entered in the class data table. Make sure of the units you are using and the number of places in your calculated results. The table should be labeled Table A with an appropriate key for any abbreviations.

The following abbreviations are used in data Table B to conserve space:

AT - air temperature
H - humidity
SM - soil moisture
ST - soil temperature
pH - acidity of soil

Combine data from at least three other groups (or as your teacher directs) in the Class Data Table B.

Table A:

STUDENT GROUP DATA

TREE #_____
SPECIES:_________________________________

. Air Temp. Soil Temp. Humidity pH Soil
Moisture
Base . . . . .
Dripline . . . . .
Outside . . . . .

Table B:

CLASS DATA

Tree No. Species Base
AT ST H pH SM
Dripline
AT ST H pH SM
Outside
AT ST H pH SM
. . . . .
. . . . .
. . . . .
. . . . .
. . . . .

Discussion Questions

  1. Which tree had the greatest difference in temperature between the base and the area outside the tree? Which tree had the least difference? What was the difference?
  2. Was the difference in humidity between the base of the tree and the open area outside surprising to you? Explain.
  3. Which trees had the greatest soil moisture at the base? at the drip line? Is there a difference? Why?
  4. Do you believe that the pH difference is due to the species of tree? Explain your answer.

Conclusions

  1. Does the data support your hypothesis? Why or why not?
  2. What does the results of this experiment tell you about trees as a homeowner / forester?
  3. What experiment could you design to learn more about the effects of trees on the environment?
  4. How are the conditions under a tree different from outside its influence?

Background Information
While the micro-environment required by an organism may not seem important to the untrained observer, the micro-environment above and below ground can have a tremendous impact on all organisms. In the last 30 years, the availability of more sophisticated techniques are increasing our awareness of the micro-environment. We have been manipulating the macro-environment without realizing how the micro-environment is also being altered.

The chemistry of the soil and the tree are now being studied intensively by scientists. Scienctific journals are now availabe that specifically address the health and productivity of trees. The three factors chosen for this exercise can be measured and compared easily. Since trees live for many years, student data on the same tree can be compared over time. The trees we plant and take care of today can be here for many generations to come.

Target Group
     High school or middle school level

Timeline
Day 1 -- Students should discuss their ideas on the macro- or micro-environment of a tree. This should include how far away from a tree we can measure the effect of the tree. The students need to discuss what factors are needed in their data tables. The students should then make their hypothesis by group and this should be checked before going out in the field. Demonstration of the equipment and its proper use are needed for accurate data recording. The student data table design should be checked, along with their equipment lists. The class data table should be a summary by groups.
Day 2 -- Students should go out to their two trees and gather the data. When finished, return to the lab and assimilate the class data. Work on calculations and discussion questions.
Day 3 -- Conduct a question and answer session after the class data has been collected and checked. Use a graphing program or have each group gather data from two other species of trees and make a graph for comparisons.

Placement of Lab in Curriculum
This exercise is part of the unit on trees and can be done once the preliminary work of organizing the science class has been accomplished.

This exercise would fit in an environmental or higher plant unit. The exercises are more effective as a coordinated unit over a two to three week period.

Student Learning Objectives

  1. Recognize that one organism will have an effect on other plants in an urban setting.
  2. Understand that the interaction among trees, soil and people is becoming increasingly important in the urban environment.
  3. Understand that data reflects the accuracy of the measuring devices.
  4. Apply quantitative observational methods to accumulate precise data about the trees at their site.
  5. Analyze the results of the experiment.
  6. Evaluate the interpretation of data collected during the experiment.

Preparation and Teaching Tips
The preparation for this experiment is the same as the preceding exercises in this unit. The need to prepare the area for the tree key exercise is the prelude to all the experiments. Once the field work of setting up the tree identification has been done by map or tree tag number, trees can be assigned to students. It is suggested that each group collect information on two trees. If there is time, or need, additional trees can be assigned. Remember that too much data is as confusing as too little.

Students should prepare a data table for the two trees they are going to study. The class data table should be the same format, so computer analysis can be done later.

The lab exercise can be done by one or two groups while other groups are doing the other labs in this packet. Plan ahead so that all the photocopied materials are prepared, and the students have prepared the proper tables and equipment lists for the exercise.

The data tables for the students are meant as an example that can either be used as is, or as a suggestion of how to set up a table. Since the organization of the data table used in the field is not important to the class, it may be prudent to let students design their own to gain experience with this process.

Blowouts

  1. Compare and contrast the north side to the south side of the tree. East vs. west.
  2. Compare different tree species.
  3. Compare different aged trees of the same species.
  4. Compare trees that have been mulched extensively to those that are surrounded by grass, or are in median strips of parking lots.

References

  1. Biology: Living Systems. Alexander, P., et al. Prentice Hall Inc. 1989.
  2. Field Biology for Secondary Students. Voss, Burton, editor. Unpublished. University of Michigan Biological Station. 1987.
  3. Tree Maintenance. Pirone, P.P., 5th edition, Oxford University Press, N.Y. 1989.

Discussion Questions Answers
To accurately answer these questions the students have to review all the class data and examine all the possibilities. The answers will vary for all the groups, and the work should be designed so it is done as a group. Any type of indepth answer will suffice with the use of pictures or diagrams to support their positions. A final report to the class on each experiment could enhance their motivation to examine one area in detail.

Table B:

example 1

-- °C --

Tree No. Species Base
AT ST H pH SM
Dripline
AT ST H pH SM
Outside
AT ST H pH SM
1 Silver maple 21 21 83 6.5 5 24 24 85 7.5 4 27 31 65 8.0 1
3 Pin oak 20 20 85 6.0 5 24 22 80 7.0 3 26 30 62 8.0 1
. . . . .

example 2

-- °F --

Tree No. Species Base
AT ST H pH SM
Dripline
AT ST H pH SM
Outside
AT ST H pH SM
1 Silver maple 71 70 83 6.5 5 77 77 85 7.5 4 80 87 65 8.0 1
3 Pin oak 69 69 85 6.0 5 77 74 80 7.0 3 80 86 63 8.0 1
. . . . .


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