Tree Identification: How To Use a Dichotomous Key

1. Identification of a Set of 10 Unknown Samples

Use the dichotomous key (Table 1) to identify the 10 unknown leaf samples (Figures 6-15).

1. Pick a leaf, and starting at number 1 on the key, answer each of the questions.
2. Choose the statement that best describes the leaf in question.
3. The column on the right lists either the tree species or a number that lists the next set of statements to consider. 
4. Continue until the key lists the name of the tree from which the leaf sample came, and fill in the blank table supplied (Table 2).

2. Field Investigation

Collect leaf samples from 5 trees, properly identify the trees using a field guide to trees, and record on a data sheet (Table 3).

1. Select a tree to be identified.
2. Collect one representative leaf sample from the tree. 
3. Glue it to a herbarium sheet with regular glue.
4. Note whether the leaves have an alternate or opposite arrangement on the stems. 
5. Record this on the herbarium sheet and the data sheet.
6. Measure the diameter at breast height (dbh) of the tree in inches.
   1. This is done by measuring the circumference of the tree at 4½ feet above the existing grade. The diameter of the tree is calculated from the circumference using the formula d = C/Π. Record the circumference and the diameter on the data sheet.
7. Note on the data sheet what type of land use is nearest to the tree: single family residential, multi-family residential, small commercial business, industrial/large commercial business, or park/other vacant land.
8. Repeat steps 2.1 – 2.7 for 4 additional trees. 5 total leaf samples should be collected.
9. Using a field guide to trees of choice, identify the leaf samples.  Record the species on the data sheet.

3. National Tree Benefits Calculator

Using this software, the benefits of street-side trees can be calculated. This includes a tree’s annual benefits for storm water management, property value, energy efficiency, and carbon sequestration.

1. Open up the iTree for education software tool found at http://www.treebenefits.com/calculator/ created by the USDA Forest Service, which means iTree tools are in the public domain.
2. Using the National Tree Benefits Calculator (Figure 16) and the data collected on the trees, calculate the environmental benefit of each tree.  
3. Record the results.

Figures 6-15. Unknown leaf samples.

Figure 16. National Tree Benefit Calculator.

1	Is the leaf needlelike or scalelike? Is the leaf a broadleaf?				Row 2 Row 3
2	Is the leaf scalelike? Is the leaf needlelike?				Red Cedar Scotch Pine
3	Is the leaf simple? Is the leaf compound?				Row 4 Row 5
4	Is the leaf lobed? Is the leaf unlobed?				Row 6 Row 7
5	Is the leaf once compound? Is the leaf twice compound?				Green Ash Honeylocust
6	Is the leaf pinnately lobed? Is the leaf palmately lobed?				Bur Oak Row 8
7	Does the leaf have teeth on the margin? Does the leaf NOT have teeth on the margin?				Row 9 Redbud
8	Does the leaf have 3 – 5 deep lobes with opposite leaf arrangement? Does the leaf have 3 – 5 shallow lobes with alternate leaf arrangement?				Silver Maple Sycamore
9	Does the leaf margin have double teeth, elliptical shape and asymmetrical at the base? Does the leaf have a single teeth margin?				American Elm Cottonwood

Table 1. Tree Identification Dichotomous Key.

Unknown Sample	Species
1
2
3
4
5
6
7
8
9
10

Table 2. A blank table to fill out tree species for each unknown leaf sample.

Tree Sample Number	Leaf Arrangement (opposite, alternate, or whorled)	Circumference at 4½ feet above grade (inches)	Diameter at 4½ feet above grade (inches) *calculated	Land Use	Species	Notes
1
2
3
4
5

Table 3. A blank data sheet to fill out leaf arrangement, circumference, dbh, land use, species, and notes.