Tree Replacement Guidelines

Trees are routinely lost from publicly owned and maintained areas for many reasons, including infrastructure maintenance and new construction. When private development affects trees within rights-of-way, the removal or replacement of those trees is governed by provisions within the County Code, site plan conditions, or other County policies and/or procedures.

Street Trees

A number of street trees will be designed into each County street improvement project to reforest or afforest the appropriate sections of the right-of-way based on spacing and other conditions, regardless of the number of trees removed. Appropriate species, quantities and sizes will be suggested by the Department of Parks and Recreation (DPR) in accordance with Administrative Regulation 4.3 or its addenda.

An evaluation of potential tree loss will be made prior to removals to determine if this reforestation or afforestation represents reasonable compensation for the total value of the lost resources. To assist in that evaluation, the following criteria will be used:

• As a minimum, trees with a caliper of 10 inches or less that are removed from the rights-of-way will be replaced on a one-for-one basis.
• Significant trees (caliper greater than 10 inches) will be replaced at a rate derived from a formula of the International Society of Arboriculture.

Replacement Tree Types and Equivalents

The number of replacement trees shall be planted according to the below ratio. View the Recommended Tree List for more information about the best types of trees to plant, and corresponding sizes of trees. Consult with your urban forester if a tree proposed is not listed.

• One-for-One Basis: One Medium, Medium-Large, or Large tree will fulfill the replacement requirement of one replacement tree per the tree replacement calculations.
• Three-to-One Basis: Three Small or Small-medium trees will fulfill the replacement requirement of one replacement tree per the tree replacement calculations.

Where the right-of-way does not offer enough space to replace the required number of trees within the project limits, the trees that cannot be accommodated will be provided to the Tree Canopy Fund in a monetary amount of at least $2,400 per tree, coordinated with the Department of Parks and Recreation (DPR).

Parks, Open Spaces and Other Public Properties

The guidelines are identical to the ones above, with two exceptions. First, shrubs and groundcover will also be designed into the reforestation. Second, replacement trees that cannot be placed at the project site will go back into parks, open spaces or other public properties (as opposed to rights-of-way) from a Department of Parks and Recreation (DPR) priority list.

Private Property

Trees removed from private property as part of a project will be replaced in accordance with the Chesapeake Bay Preservation Ordinance.

Tree Replacement Formula

Definitions

• Condition: rating from 0 (dead) to 100 percent (perfect); expressed as a percentage of 100 (e.g., 100 percent = 1; 60 percent = .6, etc.)
• Diameter: trunk diameter at 4 1/2 feet above the ground
• Species: all tree species are given a value from 1 to 100, which is expressed as a percentage of 100 (e.g., 40 = 40 percent = .4). This is a value assigned to a species according to a number of factors, including longevity, durability and appropriateness to the growing zone. Ranges of species ratings are available from the 2021 MAC-ISA Species rating guide, available here: https://www.mac-isa.org/images/pdfs/Speciesratings2021.pdf

   

Procedure

Scoring is determined by the multiplication of diameter, species and condition. Shown below are three applications of the formula.

1. A 10-inch American holly is automatically replaced with one tree, according to the above policy.

2. A 40-inch silver maple (species rating of 40), rated at 60 percent condition, is scored as 40 X .4 X .6 for a total score of 9.6.

3. A 36-inch white oak (species rating of 80), rated at 70 percent condition, is scored as 36 X .8 X .7 for a total score of 20.16.

Application to Replacement Policy

Trees are replaced at the following rates, based on the overall scores:

• 1-4.9 = one tree
• 5-9.9 = two trees
• 10-14.9 = three trees
• 15-19.9 = four trees
• 20-24.5 = five trees
• 25+ = six trees

In the examples above, the American holly is replaced with one tree, the silver maple with two trees and the white oak with five trees.

The formula should only be used by qualified individuals, like professional arborists, with the knowledge of tree condition determinations and species factors.

Practical Examples

Example 1

Note: The diameters with an asterisk (*) denote trees with 10 inches diameter at breast height (DBH) and smaller, which are automatically replaced at a rate of one-for-one according to the policy.

In this example, 18 trees are lost (1,173 caliper inches), and 20 replacements planted, since two of the trees being removed warrant greater than one-for-one replacements. However, a 36-inch sycamore is also at risk; if it dies, it will be replaced with four trees:

Example 2

Note: The diameters with an asterisk (*) denote trees with 10 inches DBH and smaller, which are automatically replaced at a rate of one-for-one according to the policy.

In this example, 11 trees are lost (209 caliper inches), and 17 replacements planted, since four of the trees being removed warrant greater than one-for-one replacements. However, the trees listed below are also in the project area and are considered to be at risk; if they die before construction is completed, they would be replaced as follows:

Note: The above examples are for illustrating the application of the formula and do not necessarily represent an actual project.