Section 4.2: Time to Collect Samples!
Identify what a tree core and soil sample is and what can be learned from them.
Examine how to properly and safely core a tree and collect soil samples and apply this knowledge in the field.
Demonstrate an understanding of how to measure the diameter of a tree.
Demonstrate an understanding of the Pythagorean theorem concretely, pictorially, and/or symbolically by solving for the height of the tree.
What is a Tree Core Sample?
A tree core sample is a cylindrical section of tree that has been drilled and removed from the tree (see Figure 11). Cores start at the bark of a tree and go into the center, or pith, of the tree. The length of the tree core depends on the thickness of the tree and how far past the pith you drill to. Please note that coring a tree does not harm it. The sampling process creates very small holes that do not inhibit the growth of the tree. They will leave a mark and the tree will fill it with sap but it does not alter the tree's ability to grow and photosynthesize.
What Can a Tree Core Tell Us?
Tree cores contain annual growth rings, which show the growth pattern of the tree each year and the scientific study of these tree rings is called dendrochronology. Before any measurements can be taken, those who study dendrochronology, or dendrochronologists, must mount the tree cores on boards and sand them down to make a flat surface. Having a flat surface makes the tree rings incredibly easy to see and allows dendrochronologists to measure the position of each ring and how the ring thicknesses changes with time.
By knowing how ideal trees should grow (see Section 6.1: Dendrochronology for more), dendrochronologists can account for the natural decrease in ring thickness to see how the tree's average growth compares from year to year. This information can be used to study the changing environmental conditions surrounding the tree throughout its life, giving insights into the climate history of the area.
Dendrochronologists are also able to determine the age of the tree by counting back in time along with the tree rings. This level of information can be used to settle historical arguments regarding the trees' or areas' age and history. If a core came from a dead tree, such as when wood is used in construction or from an artifact such as railing from the Titanic, it must be referenced to a master chronology.
A master chronology is a large set of chronologies of tree data from an area that extends far back in time and contains many key markers which help when comparing against a sample. Dendrochronologists compile these chronologies and use them to determine the approximate time when the plank or piece of wood was in a tree, giving an approximate time for when structures were built in the past. This is the subfield of dendrochronology, called dendroarchaeology.
Preparing to Collect Your Samples
Before you go out and collect your tree core and soil samples, be sure to take the time to review the videos that go through this procedure and make sure you have all the equipment you need. Remember that the TREE kit sent out by the CLS contains most of the equipment you need. Teachers can also to the students about giving back to the environment before collecting (see Module 2.4 for more information). We encourage students to use the TREE Student Field Book or bring a notebook with them as there are lots of observations and information they need to make note of when in the field.
***MOST IMPORTANT IS TO BE SURE YOU HAVE PERMISSION TO COLLECT THE SAMPLES***
When you are out in the field, remember that in order to get optimal data from the CLS and MAD Lab, we need an optimal sample. Find a trembling aspen and inspect it (see Module 1 for more information). Does it appear to be healthy? Are there any signs it is rotten? Are there any cankers or fungi growing on the tree? If there are mushrooms growing at the bottom of the tree, that is a sign the tree could be potentially rotting on the inside. Are there any scars or disfigurations on the tree? Do your best to identify a healthy tree and know that it may still be sick or rotting if it appears healthy on the outside.
As well, there are multiple tasks that need to be done during sample collection. It may be best to divide the following tasks up among students: collecting tree core samples, collect soil samples, measure diameter of the tree, measure the height of the tree, and collecting notes and observations from the environment.
How do You Core a Tree?
Please note that if you are coring during a cold month, the increment borer may freeze inside the tree if you leave it stay there long. Read over the instructions and use another person to help extract the core and remove the increment borer in a timely fashion to prevent this. If it does get stuck, try your best to forcefully and carefully wiggle and move the borer out.
TREE Student Field Book
Information in this section will help you fill out your Student Field Book when you are collecting your samples.
Ensure you have everything you need (view previous section to see what is and is not included in your TREE kit).
Remove wrapper from one straw and tape one end of one straw closed.
Unscrew the spoon (thin and silver piece) from the increment borer (blue handle) of the corer.
Remove core extractor (black piece) from the increment borer.
Unlatch the increment borer.
Insert the square end of the core extractor into the latch from the opposite side of the latch (see Figure 14). Lock the latch.
To help aim toward the pith or center most portion of the tree, line up the increment borer with a branch (see Figure 15) and use your finger to trace the branch location down the tree trunk until you have reached 1.3 meters or the chest height average. Use your measuring tape to confirm this.
Place the borer tip at the location and with one hand, firmly hold the core extractor while pushing it into the tree (Figure 16)
With the other hand, rotate the increment borer clockwise until the silver core extractor tip has entered the tree. At this point, use both hands to rotate the increment borer clockwise until the corer is halfway in the tree.
Use the long silver spoon to measure how far you have cored into the tree. You only need to go to the center of there tree. Once there, stop and proceed to the next steps.
Removing the Core
Remember, if you are coring during a cold month, the increment borer may freeze inside the tree if you leave it stay there long. Remove the increment borer in a timely fashion to prevent this. If it does get stuck, try your best to forcefully and carefully wiggle and move the borer out.
Insert the spoon concave down (meaning the bottom of the curve is facing up, just like a bowl), while pressing it against the top of the increment borer as you advance the spoon.
Press the spoon as far as you can into the increment borer but be gentle as you reach the end of the spoon. Jamming the spoon in quickly may result in bending of the spoon.
Once in, leave the spoon and place your hands on the blue metal handle. Rotate the increment borer 3 half rotations counter-clockwise.
Next, slowly remove the now upward facing spoon and carefully inspect your tree core (Figure 17). Those handling the core need to be wearing gloves as shown in Figure 17 and 18. When inspecting your core, considering the following questions.
Do you have all of your core? Is it broken anywhere?
Is the core rotting anywhere?
View Figure 18 to see an example of good and not so good samples.
If the core has broken in a couple areas but is healthy, insert the pieces in the order they leave the tree at. Make sure to take a picture of the broken core in the spoon before you put the core into the straw.
If however, you find your core is unhealthy or there are too many broken pieces (as shown in Figure 18), return the core back to the hole and try sampling another trembling aspen tree. Remember that the CLS and MAD Lab need ideal samples to provide optimal data.
Once you have an ideal tree core, take a picture of the tree core in the corer (before placed in the straw) and either print it off to send back with the samples or email it to email@example.com. This image will provide a reference for the researchers when they are removing your core from the straw. Have another student who is wearing gloves insert the tree core into the tapped straw (refer back to Figure 17). Now tape the other end of the straw. Label the sample immediately so that it does not get confused with any other sample. Labeling instructions below.
Removing the Increment Borer
Rotate the increment borer counter-clockwise until it has left the tree.
Inspect the core extractor tip to make sure it is clear of any debris. If there is any debris, clear it out using the wooden tee.
Repeat for a Second Core Sample from the Same Tree
Repeat the above process for the second tree core sample (from the same tree) but this time go 90 degrees around the tree and above or below the first core site (see Figure 19). Rotating 90 degrees allows the researchers to obtain a more representative images of the rings of a tree. In some cases, tree rings do not grow perfectly circular (sometimes on one side of the tree, the rings can be large and wide, while on the other side they are can be small and narrow). Collect your second tree core and be sure that it is an ideal sample and take a picture of it before placing it in the taped straw.
Tape the two straws together with tape and have enough extra tape sticking out so you can label the samples (see Figure 20). Your label should have your school name (can use abbreviations if you tell us somewhere what the abbreviations stand for), number of the sample (1 or 2), and put the latitude and longitude coordinates on there. Don’t forget to fill in your TREE Sample Form with the acquired information and tree observations.
How do You Measure the Diameter of a Tree?
The Diameter at Breast Height (DBH) tape is used to measure the tree's diameter and this measurement is helpful data for the MAD Lab. Recall that the DBH has two sides:
The metre side is a regular measuring tape that will give you the circumference (the total distance around the tree).
The metre diameter side will give you the diameter of the tree (a linear measurement of the center of a circle, from one side to the other). This side has been divided by the number pi (3.14159), so that by wrapping this side around the tree, you get the diameter of the tree.
Steps for Measuring Tree Diameter
First, using the metre side, wrap the measuring tape around the tree and obtain the circumference (in cm). Wrap the measuring tape around the tree. Make sure to wrap the tape far enough around that the numbers overlap with the zero point on the measuring tape. Record the circumference.
Next, flip the tape over to the metre diameter side and obtain the diameter of the tree (see Figure 21). Remember, this measurement is still in cm as well. You will use these measurements in the Human or Tool: Who's More Accurate? Activity (lesson in the next section) and the MAD Lab will need it as part of their data analysis.
How do You Measure the Height of a Tree?
The clinometer has two scales (see Figure 22):
The left scale is the inclination angle in degrees. Use this scale as it enables the researchers to use the Pythagorean theorem to calculate the height.
The right scale is an engineering percent, commonly seen before large hills in the road. Do not use this scale.
This will require at least two students to complete.
Both students are to use the large measuring tape to measure 10 meters away from the tree in the direction of least brush/trees, where student 1 will stand. Ideally, there would be a clearing for the student.
Student 1 will hold up the clinometer and line up their eye sight to the top of the sampled tree. Record the inclination angle from the degrees scale within the clinometer.
Another student may need to shake the tree to make it easily distinguishable from the surrounding tree canopies.
Student 2 will measure the height of the clinometer using the measuring tape while student 1 is measuring the inclination angle (see Figure 23). Record the clinometer height.
From here, the students can calculate the height of the tree when time permits. Use the inclination angle, some trigonometry, and clinometer height offset to calculate the height of the tree, and then fill in the Sample Form.
What is a Soil Sample?
A soil sample is a collection of soil from a specific location that has been placed in a container. Your soil samples are to be taken from the middle of the A and B soil horizons.
What Can a Soil Sample Tell Us?
Soil samples contain the chemical composition and texture of the soil horizon. By studying how the chemical composition and texture of the soil change from horizon to horizon, scientists are able to determine how useful the soil is for plant use. For example, if all of the vital nutrients for plants washes away after each rainfall, the ground will not be useful for crop growth. However, if the nutrients stay near the top horizons, the soil will be useful. Understanding the chemical composition of the soil helps to determine the nutrients available to the trees growing in the soil. If we see a large quantity of a particular element in the soil, we would expect to see a large quantity of that element within the tree.
How Do You Collect a Soil Sample?
Find a location close to your tree but far enough from large roots and trails.
Lay the tarp out close by to dump dirt from the pit.
Before digging the pit, mark out a perimeter around you that is roughly 50 cm in diameter.
Carefully remove the topsoil and vegetation in as large of chunks as possible.
Dig the pit at least 30 cm deep, placing all of the dirt onto the tarp (see Figure 24).
Using a flat spade, flatten one side of the pit to display the soil horizons.
Smooth this flat surface with the hand trowel if you have one.
Using the measuring tape, measure the depth of the pit as well as the start and end of each soil horizon.
8. Use the hand trowel to fill the canisters with soil from the A and B horizons (see Figure 25). Fill one canister per horizon. Label each canister with the horizon type and the start and end measurements of the horizon.
9. Refill the pit with the soil from the tarp (see Figure 26).
Regularly pack the soil down by stomping on it.
10. Replace the vegetation and topsoil back on top of the pit and pack it down.
11. Fill in the Sample Form with the acquired information and observations of your soil.