Introduction
Tree growth takes place not only above the ground, but below. The nutrients necessary for plant growth are available under only very specific conditions for each tree species. Trees have adjusted after great lengths of time to very specific environmental conditions that existed long before humankind came on the scene. When we place a tree in an urban setting, we need to see that its needs are met. The site that a tree lives in will be modified by the tree, if the situation is not hostile. Our intent here is to determine the soil conditions around trees that are already planted and growing.

Soils differ widely over even a small area. Good soil will be composed of 45% mineral and 5% organic matter with the other portion equally divided between air (25%) and water (25%). Large populations of microorganisms, insects and arthropods, also occupy the soil and need air to survive.

Soils are generally composed of more than one layer or horizon. The soil color and compostion distinguish these layers. Using the enclosed resources, or your textbook, find out more about the structure of soil. Soil texture refers to the size of the particles that make up the soil. These five (from large to small) are large stones, gravel, sand, silt, and clay.

This exercise will familiarize you with the technique of soil sampling. Measuring different soil layers will aid in determining the soil composition in your area.

Question

1. Is the soil beneath our trees all the same?

Hypothesis
     Students should make their own before continuing.

Materials

21" soil probe	Plastic sample bags
Tape measure	Marking pen for bags
Notebooks and pencils	Small rulers (15 cm)
Bucket with replacement soil	Flags (stakes)
Field scale	Old newspaper & rolling pin

Procedure

DAY ONE

1. Before leaving the lab you should have prepared:
1. the mass of each of the labeled sample.
2. all the necessary data tables from examples below.
3. all the necessary equipment.
2. When you arrive at each tree, stop and observe the tree, noting any special conditions to be entered in the data table. (ie. driveways, power lines, sidewalks, construction nearby, damage to the tree itself, etc.).
3. At each tree, first determine which is the north and south side, and measure 0.5, 2, 4, 8, and 12 meters in each direction with the tape. (Note in the table wherever this is not possible).
4. At each spot, take a sample as deep as possible and then note the depth from the surface where the color changes. Record the maximum depth.

Collecting Samples:
1. Draw and label a picture of each sample collected in your "logbook". (length, horizon, size of each section, color)
2. Pop the sample out of the tube and cut off the top 5 to 8 cm including the grass roots. Place all the samples from the same side of the tree in the same bag marked with the tree number and direction of the samples, (ex. Tree #25 - south). Make sure the sample is kept in the bag, tied with a twist tie; record the mass when finished.
3. Weigh the bag with the moist soil inside.

Determining Soil Water Content:
6. Remove the sample from the bag and place it on newspaper to dry overnight.
7. The next day, replace the material in the bag to find the mass of the dried soil.
8. Calculate the % soil water content from Table B.

Determining Soil Constituents:
9. Crunch or roll out all the lumps of soil using a rolling pin or other large, clean metal object. All foreign matter like leaves, twigs and roots should be removed, with as little contact with your hands as possible.
10. Samples can be run through the soil sieves, if all the soil aggregates have been properly crushed.
11. Shake the sieves for about 10 minutes, then separate them, and the mass of the soil on each sieve determined. (remember to mass the bag before you put soil into it to be massed. (ex. total mass - bag mass = sample mass)
1. Calculate the total mass and the percentage of each type of soil by dividing each mass by the total.
2. From Table E take the three parts (sand, silt, clay) that apply to the soil texture triangle and find the textural class of soil in each sample.
13. Record the final results in Table E.

Table A:

Table B: SOIL FROM FIELD COLLECTION

Soil Sample Mass	Tree #_______	Side______	Side______
A. Mass of bag		________ g	________ g
B. Mass of bag & sample		________ g	________ g
C. B-A= mass of sample		________ g	________ g
DAY TWO
D. Mass of dried soil		________ g	________ g
E. Difference of A-B=mass water		________ g	________ g
F. % water = C/A x 100		________ g	________ g

Table C:

Table D:

Analysis of Results

Table E:

Discussion Questions

1. Did any of your trees have more layers of soil than others? Compared to your classmates? Which ones?
2. Is there a difference in the distance at which there is a color change? Between different sides of trees?
3. Do you think there is any correlation between soil layers and the type of tree you are sampling? Why?
4. Is there any difference in the sides of the trees and/or tree types
?
5. Which tree has the most gravel and stones? What reason, using data, can you give for this?

Conclusions

1. Which tree had the most moisture in your group? In your class?
2. Does the data support your hypothesis? Why or why not?
1. If your hypothesis is supported by the data what would you do next if you were a scientist / forester?
2. If your hypothesis was not supported by the data what would you do next?
4. What have you learned from this exercise about trees and soil? (be specific as possible)

Background Information
Tree growth and development is dependent on the soil below. The structure, texture, color, and condition of the soil all lead to successful tree growth. Poorly drained clay soils, that are usually found in new urban areas, require a different planting procedure from the dark crumbly type soils of a forest or older neighborhoods. To find the type of soil conditions trees require, consult the publications listsed in the references.

Soils in most urban or recently developed suburban areas have been changed dramatically from what they were before towns were built. The original soil, could have been anywhere from three to six feet in your area, and was most likely scraped off. Plants must grow in soils that are much less than adequate. Even if soils were not removed, the number of trucks or vehicles that moved across your property while the house was being built, may have compacted the soils. Soils piled into big mounds until they can be spread over the landscape have again changed chemically and biologically, more so with the passage of time. Without the proper ratio of water and air in the soil, trees will not grow well.

As sidewalks, curbs and streets are installed, the gravel and chemicals used also cause changes in the soil conditions. Trees have to overcome these changes to survive. Limestone driveways raise the soil pH. Compaction of soil slows water infiltration. Water runs off some areas and puddles in others, like the large holes just dug for the trees. Landscapes are designed to move water away from foundations, and plants may need extra watering. Soils are important to tree survival and we can even see that some trees will change the soils.

Soils differ widely in their characteristics and soil science is the study of soils. Most soil studies related to plant growth has been related to farming: grains in the midwest; citrus trees in Florida; cotton in the south; and fruit trees. The work with urban trees is just beginning, and relatively few people have spent careers working on Urban Forestry or its related fields.

A ringed or spiral notebook collection of tree related stories collected from magazines or newspapers should be kept yearly for class reference. The sources of information from the daily local newspaper will astound students. The local agricultural extension service, or city library, has books on trees and even more on gardening that can be useful resources. Landscape contractors in your area, or the city forester, could provide information for students. Hardware stores can also provide information if students look at resource books in the gardening sections. The variety of resources available are numerous.

Target Group
Ninth through twelfth grade students are the intended audience. Slight modifications can be made to increase the difficulty of data analysis, or simplify it for other groups.

Timeline
The amount of time needed to accomplish this particular project will depend on the number of trees and the number of times you wish to have data for trees reported. The exercise is intented for five days of work; one day of preparation, two days of field work, and two days of laboratory data analysis.

With groups of four, this exercise can be done in conjunction with other projects in this unit. Students need one day to collect data and another to calculate and check on other student groups. The student data work-up and the conclusion should be checked by other groups for comparison. A one day field trip would be good if it served as a culminating activity for all of these exercises.

Placement of the Project in the Curriculum
This can be placed in the ecology or plant section of your units; but ideally the entire Urban Forestry unit should be used together.

Student Learning Objectives
Students will be able to:

1. Understand the interaction among trees, soil and people.
2. Use equipment properly to gather data.
3. Accurately record gathered data.
4. Draw conclusions about the nature of soil at different sites for tree growth.
5. Evaluate each site for future tree growth.

Preparation and Teaching Tips

1. The previous exercise on labeling and mapping of your school site should have been completed.
2. Trees and shrubs at your school site should be tagged with an inventory number.
3. Review procedures for how many trees to use, how the data is recorded, what units to use, what level of accuracy is required, and how each of the tools is to be used.
4. Check with a school maintenance official to see if there is any buried cables to avoid. (cable TV is usually shallow)
5. Realize that for each class, and each time you go outside, it is a different teaching situation.
6. Use a checklist of materials, so students can check out all of their equipment.
7. Make sure each group of students is prepared and has written their hypothesis(es).

Expected Results
Results will vary with sampling site. See attached class data table examples.

Blowouts

1. Use a soil auger and take deep soil profiles for chemical analysis.
2. Dig a large soil pit 3' wide x 6' long x 5' deep so root structure and soil change is easily visible.
3. Measure the depths of soil horizons and compare to data for different types of natural environments, or with their own homes.

Discussion & Conclusion Question Answers
To accurately answer these questions the students will have to compare their results with other groups. A large classroom data table on butcher paper would open up many more avenues of discussion. There are no specific answers for these questions, they are all of higher order. The simple direct questions are on the pre- and post-quizzes.

1. Groups should have differences by specific types of trees.
2. The sample farthest away from an older tree should be more dramatic than for a newly planted tree in a field.
3. This question is asked if there is a field planted tree as compared to a group planted tree (forest) sample that was used.
4. There should be a difference between north and south.
5. The tree with the most gravel can tell about the construction techniques at your school site.
6. The same species of tree should show similarities.
7. Answers will vary. Important to the development of scientific thinking in students.
8. Same as above only they must use their data to support analysis.
9. Answers will vary and is a good place to also ask questions.

References

1. Selecting & Planting Trees. The Morton Arboretum, Lisle, IL. 1990.
2. Understanding Soils. VAS (Vocational Agriculture Service) Bulletin 4052, College of Agriculture, University of Illinois.
3. Soil Structure. VAS Bulletin 4028. College of Agriculture, University of Illinois.
4. Soil Color. VAS Bulletin 4029. College of Agriculture, University of Illinois.
5. Soil Texture. VAS Bulletin 4030. College of Agriculture, University of Illinois.
6. Oakfield Soil Samplers. Instructions, 1990.
7. Screen Sieves. Bulletin 0008752. Hubbard Inc. 1991.
8. Field Biology for Secondary Students. Voss, B.E., editor, Unpublished UMBS. 1988.