Section 4.2: Collecting 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 leave a mark. Depending on the time of year, the tree may fill the hole with sap to help with healing but regardless, coring does not alter the tree’s ability to grow and photosynthesize. It is like taking a blood sample from humans. We restock our supplies and continue to thrive.
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.
Tips for Sample Collection
Review the Preparing to Sample Collect Checklist for things to do before sampling.
Review the TREE Sampling Videos (available in English and French).
In order to get optimal data from MAD Lab and CLS, we need an optimal sample. Find a trembling aspen and inspect it (see Module 1.3 for more information).
We ask that you sample from a tree with at least 10 cm in diameter so as to prevent damage to the growth of the tree.
Have a plan for students. What will they be doing?
Make note of what season/time of year you are sampling:
Sampling when the ground is frozen can be challenging to collect soil samples. You may need additional tools (such as a pick axe) to collect soil. We recognize it may be difficult and encourage your group to do their best to collect.
Note that in the cold months, when you use the increment borer it may freeze inside the tree if you leave it stay there too long. Be sure to remove the borer in a timely fashion to prevent this. If it does get stuck, try your best to forcefully and carefully wiggle it out.
Sampling in hotter months may bring out bugs!
***MOST IMPORTANT IS TO BE SURE YOU HAVE PERMISSION TO COLLECT THE SAMPLES***
How Do You Core a Tree?
Locate a trembling aspen tree with at least 10 cm in diameter to sample from (this helps minimize tree damage). Use your DBH tape to measure before starting. Ideally sample from a vertical, healthy tree. NOTE: DO NOT use the spoon while you are boring into the tree. This is for extracting the core after! Putting it in before extracting (like while boring) could damage the spoon.
Ensure you have all the tools you need as well as your Sample Form nearby.
Grab the increment borer. Unscrew the spoon (thin and silver piece) from the increment borer (blue handle) of the corer. There should be a piece of flagger’s tape at the end of the spoon, to help ensure you do not lose the spoon on the ground. Pass this to someone to hold.
Remove core extractor (black piece) from the increment borer.
On the blue increment borer, there is a latch half way (silver part). Unlatch the increment borer by sliding the moveable piece out (see Figure 14).
Insert the square end of the black core extractor into the latch so a little bit is sticking out, as seen in Figure 14. Lock the piece in place by sliding the latch back into its start position. This should make a “T” shape with the increment borer.
To help aim toward the pith or centermost portion of the tree, line up the increment borer with a branch 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 (see Figure 15). Use your measuring tape to confirm. Remember, we need the pith of the tree to ensure all the tree rings are collected.
Place the borer tip at the location perpendicular to the tree. Firmly hold the increment borer while pushing it into the tree (Figure 16).
Begin to rotate the increment borer clockwise until the silver core extractor tip has entered the tree (may need one hand to help hold extractor in place while rotating). Note this will take effort/strength to have the grooves hook into the tree to start the boring process. You may have to push hard and remember, the spoon should be removed!
Once this silver grooves have entered the tree, use both hands to rotate the increment borer clockwise until the borer is about halfway in the tree. Again, this will take effort to complete.
Use the long silver spoon to measure how far you have cored into the tree (see Figure 17). Do your best to estimate how much of the borer is in. You need to bore just beyond the center/pith of the tree. Once there, stop and make sure the borer handles are level before next steps (Figure 17).
Removing the Tree Core Sample
NOTE: If you are coring during a cold month, the increment borer may freeze inside the tree if you leave it stay there long. Take a tree core sample in a timely fashion to prevent this. If the borer does get stuck, try your best to forcefully and carefully wiggle and move the borer out.
Insert the spoon so that the curved side is touching the top of the extractor. See the graphic to right.
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. If stuck, remove the spoon gently and try again.
As this is happening, have someone remove the wrapper from one straw and using the masking tape, tape one end of one straw closed.
3. Once in, leave the spoon in place, and place your hands on the blue metal handle. Rotate the increment borer 3 half rotations counter-clockwise.
4. Next, slowly remove the now upward facing spoon and carefully inspect your tree core (Figure 18). Those handling the tree core sample will put on gloves, as shown in Figure 18 and 19.
If the spoon is stuck, insert back into the extractor gently and do more counter-clockwise rotations and/or gently wiggle the spoon free.
5. 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 19 to see an example of good samples (right image) and not so good samples (on the left).
6. 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 core in the spoon, especially if broken, 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 the left image of Figure 19), 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.
7. 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 or your CLS Education Team member. This image will provide a reference for the researchers when they are removing your core from the straw.
8. Have another student who is wearing gloves insert the tree core into the taped straw (refer back to Figure 18). Once the core is in the straw, tape the other end of the straw.
9. Label the sample immediately so that it does not get confused with any other sample. Labeling instructions follow.
You will need the Sample Code that was provided from the CLS Education Team. With your masking tape, create a tag of tape (as shown in Figure 20) around the straw which has your tree core secured in place. Write out the sample code on the tag with your marker. It may be helpful to write out the code on the tape before rolling it off the tape.
Your sample code for your tree codes will be in the format of: YYSK##T#a and YYSK##T#b, where YY is year, SK is province/territory you are from, and ## represent numbers associated with your sample set. Note that your first tree core sample you collect is “a” and your second tree core sample is “b”.
Removing the Increment Borer
Rotate the increment borer counter-clockwise until it has been removed from the tree.
Inspect the core extractor tip (end of black piece with grooves) to make sure it is clear of any debris. If there is any debris, clear it out using the wooden tee (include pieces in your sample).
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 (Figure 21). Rotating 90 degrees allows the researchers to obtain more representative images of the rings of a tree. In some cases, tree rings do not grow perfectly circular. For example, 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. Proceed to collecting your second tree. Be sure:
that it is an ideal sample,
take a picture of it,
place it in the taped straw, and
appropriately label it.
Disassemble the Borer
Once your tree core samples are collected, dissemble the borer:
Open the latch (refer back to Figure 19), remove the extractor, and close the latch.
Check inside the extractor to see if there are any remaining tree pieces. If debris remains, use the wooden tee to remove it and be sure to include this in your sample.
Now return the black extractor into the blue handle and then place the spoon in the handle as well, twisting it to secure the internal components.
Place your sampled cores in the bubble wrap and place these in the TREE Kit for holding.
Proceed to the next steps.
Measuring the Diameter of a Tree
The diameter at breast height (DBH) tape is used to measure the tree’s diameter and this measurement is necessary data for the MAD Lab’s science research. The DBH tape will be found in the black cloth case, along with the clinometer. When you pull out the DBH tape, notice that it has two sides:
The metre side is a regular measuring tape that will give you the circumference or the total distance around the tree.
USE THE METRE DIAMETER side for the diameter of the tree (shown in Figure 22). The diameter is a linear measurement of the center of a circle, from one side to the other. This side of the DBH tape 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: this is the recording we need for TREE.
Steps for Measuring Tree Diameter
Wrap the measuring tape around the tree, making sure you have the metre diameter side facing outward, and obtain the diameter of the tree. Make sure to wrap the tape far enough around that the numbers overlap with the zero point on the tape (as shown in Figure 22).
Record the DBH measurement on your Sample Form (this measurement is in cm).
Measuring the Height of the Tree
The MAD Lab Team would also like to know the height of the tree for their research. To obtain this measurement, you will need the clinometer from your sample kit (found in the small black cloth case with the DBH tape). When looking through the clinometer, note that it has two scales (see Figure 23):
The left scale is the inclination angle in degrees. This scale can be used with trigonometry to calculate the height of the tree, but there's a quicker way.
The right scale is an engineering percent, also known as a grade. You commonly seen grades indicated on signs before large hills in the road and it is the same as having the tangent calculated for you. We will use this side.
Obtaining the tree’s height will require at least two students. Follow the steps and/or check out our TREE Video 4 Part 2, covering the use of the clinometer in this part of the process.
Steps for Measuring Tree Height
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 and ideally, the student would be on level ground. Having a sloped ground will impact the accuracy of the calculations.
Student 1 will look through the clinometer with one eye (usually the dominate eye) while keeping both eyes opens. You should be able to see the scale, tree, and cross-hair line all at the same time; much like a type of optical illusion (see Figure 24).
A third student may need to shake the tree to make it easily distinguishable from the surrounding tree canopies.
The number on the right side of the scale is the one being used. Notice the plus and minus signs in between them (see Figure 24). Student 1 should look at the very top of the tree and align the cross-hair line with it. Read the number from the right-side as accurately as you can and record it as TOP.
Next, Student 1 will look at the point where the trunk meets the ground and record this number as BOTTOM (Note: this number may be negative so be sure to record the sign as well!).
Now calculate the true percent slope by subtraction:
TOTAL = TOP - BOTTOM
The height of the tree can now be found with this formula:
Height (m) = TOTAL / 100 * 10 m
Record the height on the Sample Form.
An example for calculating the height is shared in Figure 25.
Return equipment back into kit.
Human or Tool: Who’s More Accurate Lesson
Compare the accuracy in human measurements vs. tool measurements to do calculations. Lessons can be downloaded and adapted from the link: https://bit.ly/3DdJggV
Complete the Sample Form
Be sure to record your measurements in your Sample Form, plus:
Obtain the GPS coordinates (in decimal degrees) and elevation of your sampling location. Some compass apps on smartphones display this. You can also check Google Maps (helpful explanation link here) or download smartphone apps from your app store to assist.
Obtain the distance to the closest tree from the one you sampled. Grab the long measuring tape!
Observations of the sampling location, tree, and soil need to be recorded. For more detail on what we are looking for, check out our Sample Form Instructions.
Take a picture of your tree and send it either by email to your CLS Education Team member or along with your kit.
What is a Soil Sample?
MAD Lab’s research requires soil samples from two different depths, called Horizon A and Horizon B, from a pit that is dug near the base of the tree you are sampling from. These samples are placed in the canisters provided in your TREE kit (see Figure 26).
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. Module 3 covers more detail on nutrient cycles in the soil and basic soil knowledge (i.e. soil horizons). Our TREE Video 5 demonstrates how the soil sample is collected.
Note that having horizons A and B in your sampling location will vary across Canada. Check out Section 3.2 to learn more and do your best to collect what you can.
How to Collect a Soil Sample
Note that during cold months and depending on your location in Canada, the ground may be frozen when you are trying to collect your soil sample. You may need additional tools aside from your shovels to collect the soil. We recognize this may be difficult but encourage you to do your best. Have your students work on problem-solving!
Dig the Soil Pit
Find a location close to your tree but far enough from large roots and trails.
Lay the tarp out close by to dump soil from the pit.
Before digging the pit, mark out a perimeter that is roughly 50 cm in diameter. A good approach to this is making a large square with your shovel (two shovels widths per side). See Figure 27.
Creating this square will make it easy to remove the topsoil and vegetation in one large chunk and decrease the amount of disturbing the soil.
Carefully remove the topsoil and vegetation in as large of chunks as possible (Figure 28).
5. Dig the pit at least 30 cm deep or until you can clearly see the A & B horizons – the depth will vary depending on your location in Canada. Place all of the displaced soil (the dirt) onto the tarp.
6. Using a flat spade, flatten one side of the pit to display the soil horizons (see Figure 29).
Smooth this flat surface with the hand trowel if you have one.
7. Using a measuring tape, measure the depth of the pit as well as the start and end of each soil horizon. Record these numbers on the Sample Form.
Use the hand trowel to fill the canisters at least half way with soil (see Figure 30). Fill one canister per horizon and check off the appropriate soil horizon on the soil labels. If your kit did not come with soil canister labels, using the masking tape and marker will work. Be sure it is clear which sample is in which canister.
Make observations of the soil and record on the Sample Form. What does the soil look like? What is the texture? Is it dry or wet? Any smells? For additional information, check out our Sample Form Instructions or Module 3.1 for soil characteristics.
Place soil samples back into kit.
Once you have your soil samples, refill the pit with the soil from the tarp (see Figure 31).
Regularly pack the soil down by stomping on it.
Replace the vegetation and topsoil back on top of the pit and gently pack it down.