Teacher Directions for Tree Inventory Exercise

This exercise will introduce you to tools and procedures used to identify tree species and to assess a tree’s height, diameter, growing conditions, and overall health. As you complete this exercise you will become more familiar with identifying trees and assessing their attributes. This data will be entered into GIS and used as an input for the models in CITYgreen.

The tree inventory is typically conducted by a combination of students and a teacher or someone knowledgeable about trees that can provide assistance with species identification and proper data collection techniques. Evaluate the first two trees as a class allowing the students to ask questions and become familiar with the process. Then split the students in groups and give each group a clipboard with inventory sheet and similar field map, pen/pencil, tangent height gauge, tape measure, worksheet for evaluating tree condition, and a tree identification guide. Assign the students a group of trees to identify and assess.

Use one evaluation sheet for each tree. Enter name, location of inventory, and date and the evaluation form. Make sure to write down the correct tree id # of the tree you are evaluating. This information is found on your field map.

Tools needed to complete the tree survey:

• Clipboard
• Map of inventory area
• Inventory collection sheet
• Tree ID guide
• Tape measure
• Tangent height guage or a clinometer
• Pen/Pencil

1. Locate all the Trees in your Inventory Area

To begin the inventory you should have a printed map of the inventory area with all the trees labeled with a unique number. In the field, locate each tree on the site map. If a tree is not shown or is mapped incorrectly, draw its canopy and estimate its approximate canopy width and height. Assign a unique identification number to the newly drawn tree (i.e.do not assign a number that is already being used by another tree within that study area).

2. Identifying Tree Species

This dichotomas tree guide is intended to be used as a field guide to assist you in identifying trees by their leaves. Other tree guides can be used as well. Examine several leaves or needles from the same tree Beginning on page 6 with Box 6a in the dichotomas tree guide, there is a series of questions about leaves and other tree parts. Each answer leads to another question until the identity of the tree is discovered.

3. Understory Cover

Take note of the gound cover under the tree canopy.

1 = Forest Litter Understory (leaves, twigs, flower, fruit and other natural tree droppings).
2 = Grass/Turf Understory (including other vegetative groundcover).
3 = Impervious Surfaces (including all paved and unpaved surfaces (concrete, asphalt, bare soil, and compacted gravel) and whether they drain to sewer or open ditches).

4. Measuring the Diameter at Breast Height (DBH)

Measure the trunk diameter at 4.5 feet above the ground using a regular tape measure. If the tree is located on a slope, measure 4.5 feet from the uphill side. If the tree has a multi-stem trunk, measure the largest stem. Convert the circumference measurement using the formula: Diameter=Circumference/Pi (pi=3.14)

5. Calculating Tree Height Using a Tangent Height Guage

Stand far enough away from the tree so you can comfortably see the top of the crown and the base of the trunk. Do your best to stand on level ground with the tree. If there is a slope that can’t be avoided, try to stand beneath the tree rather than above it. Using the tangent height gauge locate the top of the object through the sight. Keep the level bubble centered. This creates a 45 degree angle from the tree. Measure the distance in feet from you to the base of the tree = (D). Measure your height to eye level in feet = (H). Height of Tree = D + H. Determine which height class the tree is in and record that input for CITYgreen. 1 = <25 feet 2 = 25-25 feet 3 = >45 feet

Note: If you don't have a tangent height guage you can also use a clinometer

6. Evaluate Overall Health

Evaluate overall tree health by inspecting the tree’s crown, trunk, and roots. Look for exposed roots, missing bark, decay, dead or dying branches, regrowth from previous topping or line clearance (defined as a poor pruning practice where the branches are cut back to a specific height without regard to the tree’s form or cutting back to an individual branch node), exposed tree cavity, or unbalanced foliage as signs of an unhealthy tree.

Use the Worksheet for Evaluating Tree Condition found at the end of the lesson to assist with the assessment. One worksheet is used for each tree. The evaluation criteria are divided into categories representing all aspects of a tree. Each criterion is weighted with a point value. Review all the criteria assigning points based on relevance. Following the evaluation, total the points to reveal a health rating.

Use the standard evaluation system that rates trees using a 1-5 health rating:
5 = Excellent
4 = Good
3 = Fair
2 = Poor
1 = Dead

7. Growing Condition

A tree’s growing condition generally links a tree’s ability to reach full mature size to its site characteristics, helps to predict its future size and overall viability. A forest or park tree growing in clay loam with no obstructions and minimal competition will certainly fare better than the same tree found next to a large building in compacted nutrient-poor soils. Make a determination of growing condition based upon your knowledge of the site characteristics and the individual tree’s growth preferences (if known). Things to consider are: soil type(clay loam best; pure sand or clay worst), available light (appropriate for species’ needs), nutrients, and water(not too much or too little); competition with other trees and/or woody plants; and potential for physical damage (e.g. next to a curb, in a parking lot, under low wires, growing into building etc.).

3 = Good
2 = Fair
1 = Poor

Click here to download a pdf of the Tree Inventory Exercise (pdf 2MB)
Click here to download a pdf of the Tree Inventory Data Sheet (pdf 500kb)

Contact Mike Lehman for details