Explanation of experiment and development of hypotheses (40 minutes)
Collecting data (45 minutes per tree, depending on how much experience students have with measurement techniques)
Interpreting data (1 hour)
Preparing write-up (30-45 minutes depending on experience)

Students will discover some effects of plants on the environment in their vicinity; students will collect, analyze, and interpret data.

The environment affects trees, but trees may also affect the environment. A tree needs water, minerals, carbon dioxide, and sunlight to grow. The soil pH, moisture content, type of soil, level of nearby competition from other plants, and human activities can all influence tree growth.

Air thermometer	Soil moisture meter
Soil thermometer (optional)	Small spades or trowels
Soil pH kit or pH paper	Psychrometer (optional)
Meter sticks or 100' tape	Small bottles of distilled water
Beakers	Compass

 

Students may work in small groups to collect data from one or two species of trees in a particular setting (e.g. full sun, close to a building, close to other trees).

Each set of measurements should be taken in three places:

1. immediately at the base of the tree
2. at the dripline of the tree (the distance to the edge of the canopy, this distance should be measured by students and will vary from tree to tree)
3. at least 5 m from the tree in full sun

Air and soil temperature measurements should be made at all three locations. Soil pH tests can be done by making an approximately 1:1 soil:water mixture in a small beaker and dipping the pH paper in the water after the soil has settled out (3 to 5 minutes), or by using a soil pH kit. These measurements should also be made at all three locations. If the appropriate equipment is available, students can measure soil moisture levels and relative humidity of the air at all three locations as well.

Each group of students should prepare a summary table of their findings using the worksheet. Depending on the number of student groups, the class may be able to compare measurements made on trees in different settings, or measurements made at three points moving in different cardinal directions from the base of the tree (e.g. north vs. south, or east vs. west). Discuss the results using the questions on the worksheet as a guide.

 
This exercise may be used in a unit on higher plants, or an environmental science unit. The student learning objectives include recognizing the effect of different organisms on the environment and on each other, understanding data collection, summarization, and comparison, applying quantitative measuring methods to test their hypotheses, analyzing data, and interpreting the results. Selecting trees in vastly different settings will amplify the differences-i.e. trees on islands in parking lots vs. trees in lawns, trees near buildings vs. those in the open. Results may also be amplified at certain times of year, for example, during early fall when nighttime temperatures contrast with daytime, or spring, soon after leaf expansion. Trees must be in leaf for this experiment to work.