Tree Identification: How To Use a Dichotomous Key

Overview

Source: Laboratories of Margaret Workman and Kimberly Frye - Depaul University

A dichotomous key is a tool that identifies items in nature, such as leaves. This method is based on the idea of choosing between two characteristics. The word dichotomous comes from two Greek words that mean “to divide into two parts.” In a dichotomous key for leaf identification, each pair of phrases describes different features of the leaf. Only one of the phrases correctly applies to the leaf being keyed out. The correct phrase leads to the next pair of phrases, or states the name of the tree from which the leaf came. Using a field guide to trees and the iTree National Tree Benefits Calculator helps to identify trees in a field investigation, which shows the significance of trees in terms of their environmental benefits, such as storm water management, increasing property value, energy efficiency, air quality, and carbon sequestration.

Procedure

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).

Pick a leaf, and starting at number 1 on the key, answer each of the questions.
Choose the statement that best describes the leaf in question.
The column on the right lists either the tree species or a number that lists the next set of statements to consider.
Continue until th

Results

Table 4 contains the correctly identified leaves for the identification of a set of 10 unknown species.

Results for the field investigation will vary depending on the samples collected. Representative results for trees found in the Chicagoland area (zip code 60031) can be found in Table 5.

The results for using the Tree Benefit Calculator can be found in Table 6. This calculator provides an estimation of the benefit

Application and Summary

Understanding the benefits trees provide for a community is important. Converting this benefit to a monetary value or ecosystem services value allows for a concrete understanding of exactly the role trees play in an ecosystem. Trees are important for health, the economy, and the environment, and once this is realized, a discussion about ways to protect the trees and increase their benefits can begin. As trees age and grow, their benefits increase. This provides a reason to protect mature trees (Figure 17