Before you begin the lesson, pass out the “Leaves” formative assessment handout and ask students to create groups for as many species as they think are represented. Ask students to share their answers. This is a great formative assessment prompt which will help you identify which students are knowledgeable about trees, and what similarities and differences students pay attention to when making groups. For example, some students may think that all the deciduous trees and coniferous trees are the same, while others may pay attention to the general shape of the leaves and not realize that there are several different species of maple, oak, pine, and aspen represented on the sheet. You do not need to tell students the “answers”; in fact, it is better for them to discover which trees live in their schoolyard on their own. You can hand out field guides to help students ID trees after doing the “Leaves” handout. Finally, make a class list of which species students were able to identify. Depending on your student comfort level with identifying trees, you may want to spend some time working on tree ID by using books or online resources listed in the Extend section of the lesson. You can also provide examples of bark and leaves for students to handle and classify, which will increase their confidence with identifying trees.
Using Google Earth, find your school and identify the main landscape features with your students. Have students make a simple map of the area or pass out a prepared map. Identify the locations where you will be setting up your forest plots, and have students mark the location(s) on the map. NOTE: This is a good break point if you are doing the lesson over two days. Before beginning the woodland plot activity, hand out the Tree ID worksheet. We suggest setting up at least two plots. You should also review safety procedures before going outside.
Once in the schoolyard, organize students into groups. It may be helpful to do the first plot as a class, so that students can observe the proper methods. There should be at least three people in each group, although more is fine. In their groups, students will set up the plots, record all the trees within the plot (a 30x10m rectangle), gather basic data about each tree (DBH, general health, canopy cover), and mark the tree’s location on the grid.
Remind students of some basic rules:
- Only measure trees that are larger than 10cm DBH.
- If a tree is more than halfway outside of the plot, do not count it.
- Do not measure dead trees.
- If a tree splits into two branches below the DBH line, measure each stem as if it were its own tree.
The plot should look something like this:
Once students have identified the starting point of a plot, they walk up and down the sides of the transect tape, measuring each tree that is within the 5m perpendicular from the tape. You end up with a rectangular plot.
Within the plot, students should mark the location of the trees on the accompanying grid in the worksheet. Remind students to label each tree with its tag #. You will use this information in the dispersal lesson (if applicable). Here is a sample of what this might look like:
Explain: The first step to understanding a forest ecosystem is knowing which trees live where, and calculating species richness, evenness, and other measures of biodiversity. Simple health measures such as how many trees are alive/dead etc. can also be performed. Then, using the basic information about the forest community that was collected (DBH of trees, health, location, and amount of sun), students can begin to understand more about the community. Below are some ways to delve more into different aspects of forest ecology after this initial investigation.
Have students calculate the species richness, evenness, and possibly the Shannon or Simpson’s diversity index for each plot. Then, ask students to compare the plots and provide explanations for the differences. Instructions for calculating biodiversity indices can be found in the “Biodiversity Index” handout.
One way to determine how many trees are in your plot is to simply count how many trees there are, and the next step would be to find the stand density, or the number of trees of each species. However, what these measurements don’t tell you is how large the trees in your plot are, and this means you can’t really tell much about their economic or ecosystem value. Basal area is one way to determine how much of your plot is actually covered by trees – literally, it is the area of trees in an area of land. To calculate the basal area of a tree, use the formula for the area of a circle (area=πr2). However, since you measured the diameter of the tree using the DBH tape, you have to first divide the diameter in half. Here is the formula:
Basal area = π x (diameter/2)2
For example, if the DBH of a black cherry tree is 21.9cm, its basal area is 377cm2. Most land managers report basal area in square feet per acre, but we’ll use metrics for our work. If you add up all of the basal areas for each species, the number provides you with a way to compare which of the species in your plot cover the most area. Then, you’ll need to divide by the size of your plot. Here are some data from a Cary Institute plot:
From these data we can see that black locust and sugar maple have the largest basal area. However, we don’t know if this is because of a few really large trees or lots of smaller trees. We can get a better understanding of the size of the trees by looking at the stand density, or numbers of trees in the plot:
A final way to look at these plot-level data would be to find the average diameter by species:
Biomass & Carbon storage
To get a measure of biomass and carbon storage, we need to know a bit more about the trees themselves. For example, some tree species are more dense than others, or tend to have more branches. You can calculate the biomass and carbon storage of the trees in your schoolyard plot by using the provided spreadsheet or equations list.
The Leafsnap app: http://leafsnap.com is a useful resource for identifying trees. To find out more about the ecosystem services provided by the trees on your school campus, try using the iTree program: http://www.itreetools.org/design.php . You’ll need to use the map feature to find your school. Next, add the boundaries of your school building using the drawing tools. Finally, add the trees in your schoolyard, including the species and size. This will allow you to find out how the trees are benefitting your school. Another option is to input the trees into the Hudson Valley Tree Guide on iNaturalist: http://www.inaturalist.org/projects/hudson-valley-tree-guide . You can add observations of the trees you have found in your schoolyard. Make sure to add at least one picture from your tree!
Evaluate: Using exit slips, ask students to answer the following: Name two tree species in your schoolyard, and describe the differences between these two species.