Grade: Senior
Subject: Science

#59. Tree Bagging

Science, level: Senior
Posted Tue Sep 29 10:03:19 PDT 1998 by Ken Baxter (
Beall High School, Frostburg, MD 21532
Materials Required: tape (duct recommended), transparent bags, balances
Activity Time: 2-3 periods
Concepts Taught: Water Cycle, Photosynthesis, Transpiration, Rain Forest

Environmental Science Investigation
Tree Bagging to Explore
Evapotranspiration and the Water Cycle

The most poorly understood part of the water cycle is the process of evapotranspiration by which plants give off water from their leaves to the atmosphere. The process of transpiration, was greatly ignored in most introductory science courses and only lately is entering science curricula as rain forests, a major source of atmospheric water, continue to disappear at an alarming rate.
In this investigation, tree parts will be bagged and a water transpiration to biomass ratio will be calculated from the collected data.

Objectives: 1) Bag trees (technique will be demonstrated in class).
2) Determine mass of water given off.
3) Determine mass of tree part.
4) Calculate water mass to tree mass ratio (divide grams of water by grams of tree and label water mass/tree mass).

Procedure: Make a 'Data /Calculations' section on your paper and show all data recorded. In that section make a chart or table as shown below to place your data in. Make sure you use units on all numbers. Show your calculations.

1) Tree + Bag + Water + Tape __________ grams
2) Dried Bag + Tape __________ grams
3) Dried Tree __________ grams
4) Water = #1 -(#2 + #3) = __________ grams

1) Bag the trees after class demo. Make sure the tape is a snug fit and touches both the tree and bag all the way around. Allow the trees two or more days to photosynthesize if possible. Read the steps below and set up an appropriate data table.
2) Carefully collect the bagged tree parts so as not to lose any water. Keep the opening upward.
3) Mass the bag, tree parts, and water together.
4) Separate the tree parts from the bag and tape. The water may be poured out now.
5) Mass the dried bag and tape after waving in the air to dry.
6) Mass the tree parts after waving in air to dry. Pick up any leaves or needles that fall to include them.
7) By subtraction, determine the mass of water. (
8) Determine the ratio by dividing the water mass by the mass of the dried tree parts. ( #4 / #3)

Analysis: 1) If the area you bagged had a volume that was 1 ft3, how much water would you expect to see transpired for a tree that was 1000 ft3?
2) If there are 40,000 trees of the size in question 1 above in an area, how much water would they give off in the length of time that you had your trees bagged?
3) In six months, how much water would the 40,000 trees put into the atmosphere?
4) How and why would the following factors probably affect transpiration?
Length of Day
Time of Year
5) Look at your water to biomass ratio. Notice that it shows how much water is transpired for each unit of tree biomass. How long would it take the tree to put water equivalent to its entire mass into the atmosphere?

Conclusion : Write a short paragraph commenting on what you learned from this activity.