Lab Exercise: Forest and Trees
Intro to Environmental Science, ENVS 101
Forests are important to human well-being and to the health of the planet. They provide raw materials for
food, fuel, wood and medicines and other economic products, but the ecological services they provide are
vital and often undervalued. Healthy forest ecosystems are ecological life-support systems. Forests store
carbon, preserve soils, filter water and nurture a diversity of species. These non-timber benefits are known
as “ecosystem services.”
Lab Objectives:
At the end of this lab, students should be able to:
 Operate ecological field equipment such as an clinometer, soil thermometer, compass
 Measure the height of trees using a clinometer and basic trigonometry
 Estimate the age of trees using tree core samples (?)
 Explain important ecosystem services provided by forests, including contributions to the water cycle
and atmospheric chemistry
Field equipment and supplies
Field observations – each group should
have these supplies when we go outside:
Calculator
Clinometer
Soil color book
Compass
Thermometer
Tape measure
Clipboard
Graph paper
Classroom:
Tree core samples ?
Graph paper
Calculator
Ruler
Part 1: Field Survey
For this part of the lab, we will go outside to practice some field mapping techniques, including the
measurement of trees. Your group will produce a simple map that shows the location of trees (your
instructor will tell you how many and which trees to map). You will then take some measurements and
record your results in the field table.
☐
Orientation
Your base map is a rectangle that is a scaled representation of the outdoor
study area. Each 1 inch on the map corresponds to 10 feet in reality. In order
to locate the tree(s) in the proper location on the map, follow these steps:
A. You will start at the southeast corner of the field area. Each group will have
1-2 compasses to share. Practice using the compass to locate the
directions (north, east, south, west). Note that the base map has a north
arrow. When you map your trees, you will need to correct for magnetic
declination, the angle between magnetic north and true north at your
location on Earth. Magnetic declination is about 16 degrees in Gig Harbor.
Correct for this by adjusting each direction 16 degrees to the west
(counterclockwise). See the example at right for San Francisco where the
needle is pointing to magnetic north, 14 degrees east of true north.
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B. You will need to estimate the stride length for at least one student in your group. To do this, the
students will begin at some location (it doesn't matter where you start or which direction you walk)
and take 10 normal steps. Team members will measure, using the measuring tape, from the
beginning to ending mark, in feet. The average stride length for that student is measured by dividing
the measured distance by 10. Record the stride length in your field table. You can do this for all
members in your group if you wish, or you can do it for 1 group member that your group will
designate as the “strider”.
C. Starting in the southeast (SE) corner of the field area, one student (the “strider”) should use the
compass to walk north until they are abreast with the first tree that needs to be mapped. Note the
number of stride lengths in the north direction. The strider will then turn to the west and walk until
they reach the tree. Note the number of stride lengths in the west direction. For each direction,
multiply the number of strides by the strider’s stride length (measured in the previous step). Write
your results in your field table. When you return to the classroom, you will be able to make a mark on
your map to indicate the location of the first tree.
D. Repeat step C. for any other required tree(s). See your instructor for instructions on which trees to
map.
☐ Estimate the height of your tree. Complete these steps for each required tree. When doing an
ecological survey of forests or other sites that have trees, it’s often necessary to determine the height of the
trees. This is useful for determining biomass or carbon balance sheets, for example. This is a method that
can be used to determine the height of trees (or other tall structures) from the ground. The drawing below
shows a forester measuring a tree's height using trigonometry. Assuming that the tree is at a right angle to
the plane on which the forester is standing, the base of the tree, the top of the tree, and the forester form
the corners of a right triangle.
A. For tall trees, clinometer measurements are taken from a distance at which the top of the tree can be
seen. For the relatively short trees in our field area, you will make your measurements from a
distance of roughly 10 feet (?) from the tree. One team member will stand at this distance, facing the
tree. Other team members will use the tape measure to record the distance from the tree to the
observer. Remember to write all data in the field table.
B. The observer will hold the clinometer at eye height and line it up with line of sight to the top of the
tree. (Your instructor will explain how to use the clinometer at the beginning of the lab period.) Note
the angle (θ) and record in the field table.
C. Calculate height in feet as, y = x × tangent θ
D. Repeat steps B-C for all required trees.
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☐
Soil description
o
o
o
o
o
☐
Observe the soil. Is it similar on all parts of your site (at each tree location) or are there areas that
are much drier than others or areas with distinct soil differences?
Next, note whether the soil seems dry/dusty, moist or wet/waterlogged for each tree site.
Use your soil temperature probe to measure soil temperature at a depth of about 4-5 inches.
Use your soil color book to determine the color of each horizon.
Describe the soil texture as mostly sandy (coarse), silt or mostly clay (fine) particles.
Air characteristics
o
o
o
Record the air temperature with a thermometer (include units).
Look at the sky. Each student should estimate the percent cloud cover from 0-100%. Average these
and record on your paper.
Overall weather conditions (overcast, raining, sunny, humid, windy etc.)
☐ Other field descriptions. Complete the field table by noting all of the following.
o
o
o
Date and time
Your location (the name of the field area).
A general description of your field area (near the road, hillside, behind a building, open space…)
You can do the calculations and complete the map as a group when you return to the classroom.
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Part 2: Understanding Ecosystem Services Provided by Forests
For this part of the lab, you will use the explanations and diagrams provided below to answer the following
questions. You can work individually or with your group to discuss answers, but each person will turn in their
own answer sheet for this part of the lab.
Tropical Forests: a Source or Sink of carbon? From The Carbon Cycle (from NOAA esrl.noaa.gov).
Carbon is exchanged or “cycled” among Earth’s hydrosphere, atmosphere, biosphere and geosphere. All
living organisms are built of carbon compounds. It is the fundamental building block of life and an important
component of many chemical processes. It’s present in the atmosphere primarily as carbon dioxide (CO 2),
but also as other less abundant but climatically significant gases, such as methane (CH4).
Figure 1. Summary of Carbon Cycle.
Sources and Sinks
Because life processes are fueled by carbon compounds which are oxidized to CO2, the latter is exhaled by
all animals and plants. Conversely, CO2 is assimilated by plants during photosynthesis to build new carbon
compounds. CO2 is produced by the burning of fossil fuels, which derive from the preserved products of
ancient photosynthesis. The atmosphere exchanges CO2 continuously with the oceans. Regions or
processes that predominately produce CO2 are called sources of atmospheric CO2, while those that absorb
CO2 are called sinks.
Why is the Carbon Cycle important?
While CO2 is only a very small part of the atmosphere (0.04%), it plays a large role in the energy balance of
the planet. CO2 in the atmosphere acts like a blanket over the planet by trapping longwave radiation, which
would otherwise radiate heat away from the planet. As the amount of CO2 increases, so will its warming
effect. CO2 is the largest contributor (currently 63%) to this effect by long-lived gases and its role increases
each year. The additional burden of CO2 in the atmosphere will remain for a very long time, of the order of
thousands of years, if we have to rely on the natural mechanisms of erosion and sedimentation to process
the added CO2.
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What do we know about the Carbon Cycle?
Owing primarily to the burning of fossil fuels and secondarily to changes in land-use, the amount of CO2 in
the atmosphere has been increasing globally since the onset of the Industrial Revolution. Based on 50 years
of direct observations of the atmosphere, it is clear that this trend continues and is accelerating. From
observatories and cooperative sampling sites around the world, NOAA measures global greenhouse gases
and works with partners to improve the accuracy and reliability of these measurements in order to improve
our understanding of the sources, sinks, and trends of this important gas and to improve our predictive
capability. This continuing record is critical to understanding the potential evolution of global climate as well
as aiding or verifying international management strategies.
Figure 2. Atmospheric CO2 fluctuations. The dashed red line (fluctuates periodically) represents the monthly
mean values, centered on the middle of each month. The black line with the square symbols represents the
same, after correction for the average seasonal cycle.
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Figure 3. The location of tropical rainforests.
Figure 4. This map shows the amount of carbon absorbed by plants (both on land and in the ocean) per square
kilometer, called net primary productivity, in 2002. The Amazon Rainforest is a major reservoir of stored
carbon. The Amazon accounts for 10% of the carbon consumed by land vegetation, even though it is only 5%
of the land area. (Image by Reto Stöckli, based on data provided by the Modis Science Team)
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Part 2 Lab Questions.
1. Look at Figure 2. Atmospheric Carbon Fluctuations. Why are there fluctuations in atmospheric
CO2? What is the period of fluctuation (what is the length of time between successive peaks)?
What do you think is the cause of this?
2. Approximately what percentage of Earth’s land surface is covered by tropical forests?
(estimate from figure 3)
3. Look at figure 3 and figure 4. Make a statement that compares location of tropical forests to
primary productivity rates. Explain what this means.
4. Based on this observation, how does the reduction of forested area affect the carbon cycle?
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Now we’ll take a closer look at ways that forests are involved in the Carbon cycle.
5. On the line next to each of the processes listed below, write “source” if carbon is released by
forests during the process, or “sink” if carbon is taken in by forests during the process.
__________ photosynthesis by forest trees and other producers
__________ respiration by forest trees and other producers
__________ decomposition of dead organisms in forest
__________ forest fires
__________ soil erosion (soil removed from the forest)
__________ deforestation
__________ diffusion by streams in forests (CO2 dissolved in or released by water)
6. How are forests affected by climate change? List impacts that can result as temperatures warm
and climate is affected in other ways.
7. How do forests affect climate?
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Field Table for Part 1 of Lab. Record your observations, measurements,
calculations and notes here.
Group Members:
Stride length (ft):
Location of Tree 1
(relative to SE
corner)
Distance north (ft):
Distance east (ft):
Location of Tree 2
(relative to SE
corner)
Distance north (ft):
Distance east (ft):
Height of Tree 1:
Observer’s
distance to tree
(ft):
Angle to top of
tree (degrees):
Calculated height
of tree (ft):
Height of Tree 2:
Observer’s
distance to tree
(ft):
Angle to top of
tree (degrees):
Calcualted height
of tree (ft):
Soil characteristics:
Air characteristics:
Other observations:
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