The Minnesota Tree and Woodland Carbon Capture Challenge is a friendly competition for Minnesotans to learn about the role of trees as a natural climate solution.
Participants will take measurements at the beginning and end of the 2021 growing season to determine how much carbon their trees capture from the atmosphere. This is a family-friendly activity to help explore your woods.
Trees and climate change
Trees are a natural climate solution, absorbing carbon from the atmosphere and storing it as wood. This means that healthy growing trees increase carbon sequestration and help offset greenhouse gas emissions.
According to recent estimates in the United States, forests remove about 11% of total carbon dioxide (CO2) emissions from the atmosphere. This is a motivation for keeping healthy trees and forests on the landscape.
Minnesota woodland owners own 40% of the state’s forests or about 6.8 million acres. The American Forest Foundation estimates that across all forest ownerships, private woodland owners have the greatest opportunity to mitigate the effects of future climate change through storing and sequestering carbon in their trees and woodlands.
In Minnesota, this is especially true. Our diverse forests from the North Woods in northern Minnesota to the Blufflands in southeastern Minnesota present a rich opportunity to contribute to natural climate solutions.
There are two categories in the Minnesota Tree and Woodland Carbon Capture Challenge: Single Trees and Woodlands. You can enter one or both categories. There is only one entry allowed per team per category.
For both categories you need to measure the same tree(s) at two points in the growing season:
- Measure at the start of the growing season. Measurements will not be accepted after May 31, 2021.
- Measure at the end of the growing season. Measurements will not be accepted after October 1, 2021.
In this category, you will select a single tree and measure it at the beginning and end of the 2021 growing season.
Here are the steps:
- Select a tree. The tree can be growing in a yard, along a street or in a woodland.
- Identify the species of the tree and measure the tree’s diameter at breast height, measured 4½ feet above the ground. Record the species and diameter in a notebook or digital device.
- At the end of the growing season, measure the same tree again.
- Report your species and diameter at the beginning and end of the growing season.
Tips on how to measure a tree’s diameter at breast height
Always measure the tree at 4½ feet above the ground.
A diameter tape is the best tool for measuring diameter. It converts linear distance to diameter measurements on one side of the tape, making it easy to read the tree's diameter.
If you don’t have a diameter tape, you can measure the circumference of a tree at 4½ feet above the ground with a piece of yarn or string, then do a little math to find the diameter. Here is the formula for determining a tree diameter from its circumference:
Tree diameter = Circumference / 3.14
You’ll recognize that 3.14 is pi, the mathematical constant. There’s a lot of math involved in measuring trees!
You might have a tree that is shaped oddly or is growing in an odd position. Generally, you should always measure a tree on the uphill side (see example A), above any tree defects or deformities (example B), and perpendicular to the orientation of the tree (example C). In the case of example C, two stems that originate from the same stump would be considered two separate trees.
Example: Carbon in a single tree
You measure the diameter of a sugar maple tree at the start of the growing season to be 10.5 inches. The tree stores 436 pounds of carbon.
You remeasure the same tree at the end of the growing season to be 11.1 inches. The tree now stores 510 pounds of carbon.
Importantly, the tree sequestered 74 pounds of carbon during a single growing season. This amount is equivalent to:
- The greenhouse gas emissions from 306 miles driven by a typical passenger vehicle
- The CO2 emissions from 13.9 gallons of gasoline, and
- The CO2 emissions from charging 15,735 smartphones.
In this category, you will measure many trees in a woodland at the beginning and end of the 2021 growing season.
Here are the steps:
- Select a woodland. The woodland should be at least one acre in size.
- Find a representative spot in your woodland and identify a plot center. Mark the plot center with a post or stake.
- You will revisit this same spot at the end of the growing season, so make sure you mark it so that you’ll be able to find it again later.
- Set up a 1/20th acre fixed-radius circular plot from your plot center. This plot will have a radius of 26.3 feet.
- Measuring all of the trees in an acre is too time-consuming, so foresters will typically measure a 1/20th acre plot to get a representative sample of the trees.
- In the 1/20th acre sample plot, identify all trees that are greater than five inches in diameter at breast height.
- The number of trees will vary depending on your woodland, but you will likely measure between 5 and 30 trees.
- Identify the species of each tree and measure each tree’s diameter at 4½ feet above the ground (see above).
- Remember to only measure the trees that are greater than five inches in diameter at 4½ feet above the ground.
- Record the species and diameter in a notebook or digital device.
- At the end of the growing season, measure the same trees again.
- Report your species and diameter measurements here at the beginning and end of the growing season.
Tips on how to measure a woodland
Watch this video by UMN Extension (up to minute 3:00) to see what measuring a 1/20th acre fixed-radius plot looks like. In the example video, we counted 8 trees in our 1/20th acre plot:
Also, you might make a mark on each tree at the spot where you measure the diameter at breast height. This could be done with a small piece of chalk or nail on a small portion of the bark. This will make it easier to re-measure the trees consistently at the end of the growing season.
Example: Carbon in a woodland
You measure the diameter of eight trees in your measurement plot at the start of the growing season. These trees included both oaks and pines. Here’s the data:
Measurements of trees at the start and end of the growing season
|Tree number||Species||Diameter at BEGINNING of growing season (inches)||Diameter at END of growing season (inches)|
At the beginning of the growing season, the woodland stored 17,768 pounds of carbon per acre. At the end of the growing season the woodland stores 19,066 pounds of carbon per acre.
Importantly, the woodland sequestered 1,298 pounds of carbon per acre during a single growing season. This amount is equivalent to:
- The greenhouse gas emissions from 5,356 miles driven by a typical passenger vehicle
- The CO2 emissions from 243 gallons of gasoline.
- The CO2 emissions from charging 275,297 smartphones.
Whether you choose the Single Tree or the Woodland category:
- Complete your pre-growing season measurements before May 31, 2021.
- Before the end of May 2020, Extension forestry specialist Matt Russell will email you an estimate of how much carbon is stored in your tree or woodland.
- Complete your after-growing season measurements before October 1, 2021.
- After all measurements are collected, Extension forestry specialist Matt Russell will email you an estimate of how much carbon your tree or woodland sequestered throughout the growing season.
- Winners of the Minnesota Tree and Woodland Carbon Capture Challenge will be announced in the October 2021 My Minnesota Woods newsletter. (Winners will be notified in advance).
Win a prize!
The team that sequesters the most carbon will win a cribbage board made from reclaimed urban wood. One cribbage board will go to the winner of the single tree category and one to the winner of the woodland category.
Last year, the tree that sequestered the most carbon was a silver maple in Ramsey County. This tree stored nearly 5,000 pounds of carbon and was 27.9 inches in diameter at chest height.
The woodland that sequestered the most carbon was located in Hubbard County. This woodland had a diversity of species, including aspen, basswood, sugar maple and bur oak. It stored 35.9 tons of carbon per acre and sequestered an additional 1.3 tons of carbon per acre during the growing season.
Carbon and climate
- The chapter on Climate Change and Your Woodland: Assessing Risk and Adapting to Change from the Woodland Stewardship book, written by Stephen Handler, Kris Tiles and Jennifer Teegarden, outlines practical ways that woodland owners can assess risk and adapt their woodland to future changes.
- UMN Extension’s Carbon in Minnesota’s Trees and Woodlands has a number of useful facts on forest carbon.