Examining Short-Term Tree Growth and Environmental Variables near Philadelphia, Pennsylvania

Laura Guertin, Penn State Brandywine
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Initial Publication Date: August 8, 2014 | Reviewed: December 14, 2014


The Smithsonian Institution's Global Tree Banding Project is a citizen science program that contributes to research about tree biomass by tracking how trees respond to climate. Students around the globe are monitoring the rate at which their local trees grow and learn how that rate corresponds to Smithsonian research as well as comparing the work to other students worldwide.

But at Penn State Brandywine, we are going beyond the requirements of the Smithsonian project. Instead of only taking two measurements in the spring and two measurements in the fall, undergraduate researchers are taking measurements every two weeks. We started taking measurements of ten trees on campus April 3, 2012, and we will continue until each and every tree outgrows its tree band. As a result, we have a rich database that not only contributes to scientific research but can serve as a foundation for student inquiry-based projects. The data is available for download in Google Spreadsheets for students to examine changes in tree diameter within one or between growing seasons, supplemented with temperature and precipitation data.

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The setting up of the tree bands and subsequent data collection can be conducted by students in middle grades through the university level. Analysis of the data can be carried out within the same grade levels, pending the depth at which the student wishes to work with the data. The exercise as presented here has been used in an introductory-level geoscience course for non-science majors, with gap width measurements taken on trees banded at the Penn State Brandywine campus, located 15 miles outside of Philadelphia.

Skills and concepts that students must have mastered

Students must know how to work with data in spreadsheets - specifically, how to plot data in Google Spreadsheets or MS Excel. Students should have a basic understanding of how scientists predict current, rising CO2 levels are impacting tree growth.

How the activity is situated in the course

The activity (processing the collected data) is conducted during class time, and can be completed in one laboratory period or two lecture-only classes. If a final analysis/report is requested from the students, this would be completed outside of class time. This exercise is part of a collection of exercises students complete relating to climate science (such as the Mauna Loa CO2 exercise at http://serc.carleton.edu/introgeo/interactive/examples/co2.html). This exercise will typically be the final exercise in a climate unit, as it deals with the most recent record in the local area.


Content/concepts goals for this activity

The overarching goal is to provide students an authentic data set, collected by students from their own campus environment, that documents local environmental changes that can be compared to global data. Students will have already learned about the global CO2 record over time from previous lectures/in-class exercises. This exercise will show students local data from a much shorter timescale.

Higher order thinking skills goals for this activity

Analysis of data - including plotting, generating plots of data across different scales, and examining multiple data sets (gap width, temperature, precipitation)

Other skills goals for this activity

Ability to examine geographic distribution of data with different tree species; ability to make future predictions and design a similar experiment on their own campus; report writing (if part of the final assignment outcomes)

Description and Teaching Materials

Dendrometer (tree) bands were placed on ten trees at the Penn State Brandywine campus in 2012. Students have been taking measurements every two weeks of the gap in the bands with digital calipers to establish a baseline for growth. The background information and tree measurements for the trees at Penn State Brandywine can be found at: http://sites.psu.edu/treebanding/.

There are many variations of this activity an instructor can implement, depending upon the grade level, mathematics background of students, and time available.

  • Instructors can provide students a blank x-y graph (x axis as time, y axis as total gap width) and ask students to draw a line of how they predict the trees on campus have grown over time. Ask students if there is a difference in how much a tree grows over time across different species, depending upon location on campus, and why they believe so.
  • Instructors can provide a Google Spreadsheet to students for one tree along with a pre-set x-y axis for plotting, or require students to generate their own scales for the axes. Ask students to define the growing season for the tree species and how much total growth has occurred. Ask students if the same amount of growth has occurred from one year to the next and why the growth has been the same or not. Ask students to make predictions of what they will see with other tree species and if the gap width data over time will be the same for all ten trees on campus. *Note this can be set up as a jigsaw, where teams of students can each get a different set of tree data, and then the groups compare.
  • Instructors can provide students just the gap width measurements (Column B in the spreadsheets) and have students calculate the total gap width growth over time before plotting.
  • Instructors can ask students to examine the temperature and precipitation data over the same time periods and see if there is a connection between the growth season, amount of growth within a season, and change over multiple seasons.
  • Instructors can ask students to predict what future measurements might be in the next month, next six months, next year, etc.

Questions for students:

  • On the website of The Smithsonian Tree Banding Project, they state: "At the minimum, we would like two measurements in the spring and two in the fall to help us monitor the growing season." Is two measurements each in the spring and fall enough to accurately record the growth pattern of these trees? Why/why not?
  • Is increasing CO2 in the atmosphere impacting tree biomass? Can that be determined from these data? What other factors might impact tree biomass?
  • Some of the trees have outgrown their existing tree bands. What might be a future direction for this project? Should the tree bands be re-established on the same trees, or what other data can/should be collected? Which trees would you place tree bands on at your campus, and why?
  • Would the trees at Penn State Brandywine grow at the same rate and during the same times as trees on your campus? Why/why not? (Can the same trees be found in your location?)

Teaching Notes and Tips

This exercise presents an opportunity to teach students about the differences between a line graph, scatter graph, bar graph, etc., and how best to represent the data for the research question being asked.

As stated above, instructors may want to download and modify the existing Google Spreadsheets to challenge the students more when working with the data (one suggestion is to remove the Interval Gap Growth and Total Gap Growth column, and have students compute this data themselves using formulas in Spreadsheets/Excel).

Instructors may also want to show students NBC Learn's Changing Climate: Survival of Trees for some background on CO2 increase, the impact on plant growth, and how scientists are looking at records further back in time with tree ring data.


The assessment will vary, pending the initial objective for having students work with the existing data set (plotting data from one tree, comparing tree data, examining one season versus across multiple seasons, bringing in temperature/precipitation data, etc.). Grading for this assignment can be based upon the accuracy of working with the data in the spreadsheets, generating graphs that plot the correct data points in the correct format for interpretation, interpretation of the data, and/or suggestions for future directions of the research.

References and Resources

Penn State Brandywine Tree Banding website: http://sites.psu.edu/treebanding/

Smithsonian Institution's Global Tree Banding Project website: https://treebanding.si.edu/

Curriculum resources (K-12), newspaper and journal articles: https://treebanding.si.edu/Resources/

Related modules found on the SERC website include: