Overview

The effort to include trees and forests as key components 

of green stormwater infrastructure has been championed 

by the State forestry agency, Vermont Department of 

Forests, Parks and Recreation, for a number of years. 

Starting in 2010, the State’s Agency of Natural Resources 

convened private and public stakeholders in a green infrastructure roundtable that resulted in strategic plans and 

initiatives to promote low impact development and green 

stormwater infrastructure (GSI) across State agencies, 

local governments, and professionals.

As a component of this effort, the State forestry agency 

secured a Federal grant that advanced several strategic 

actions, including hiring a green infrastructure coordinator within the State’s stormwater agency (Department of 

Environmental Conservation) who helped facilitate the 

adoption of new policies and practices. Through the grant, 

a consultant was also hired to complete a comprehensive 

review and set of recommendations on options to 

credit trees within the State’s stormwater management 

framework.

During this time, the upcoming revision of the State’s 

stormwater management manual provided a key window 

of opportunity to advance the green infrastructure 

recommendations into policy. The initial draft version of 

the manual included stormwater credits for reforestation 

(active and passive) but no credit for single tree plantings. 

In subsequent stakeholder meetings and public comment, 

support for a single tree credit was voiced; the State 

worked with partners to incorporate this into the final 

manual that was officially adopted in 2017. A complementary GSI Toolkit was developed to aid local governments in 

crediting trees and other GSI practices on smaller development sites that are not covered by the State’s permitting 

process (Vermont League of Cities and Towns 2017).

The science behind it

To establish a sound basis for establishing stormwater 

credits for trees, the State forestry agency contracted with 

Stone Environmental, Inc., to review existing research 

and policy examples and draft recommendations.

Stone Environmental, Inc., developed two white papers 

for the project. The first, describing the stormwater 

management benefits of trees (Moore and others 2014a) 

summarizes scientific knowledge about the tree processes 

that affect stormwater runoff (interception, transpiration, 

infiltration, and pollutant removal) and reviews considerations for maximizing stormwater benefits at the tree or 

site scale (soil restoration, engineered tree systems, tree 

selection, siting, and planting practices).

The second white paper (Moore and others 2014b) 

reviews examples from 12 States around the country that 

illustrate integrating tree retention or planting practices 

into stormwater programs. It also reviews over a dozen 

examples of green infrastructure crediting/incentives at 

the municipal scale, including examples from Seattle, WA, 

Washington, DC, and Nashville, TN.

U.S. Department of Agriculture

Stormwater Credits for Trees: 

Vermont Case Study

Where: State of Vermont

When: Adopted in 2017 in the Vermont Stormwater 

Management Manual Rule

What:

» Volume reduction credit in State stormwater 

permits. 

» Three tree Best Management Practice (BMPs): 

Reforestation (active and passive), single tree 

planting.

» Companion local crediting framework for 

smaller sites not covered by State permit.

Quick facts

Forest Service FS–1146c JUNE 2020
The findings from these reviews helped inform the 

credits that were adopted in Vermont, taking into account 

regulatory concerns and stakeholder input.

How the credits work—State credits

The Vermont Department of Environmental Conservation 

Stormwater Program issues permits for post-development 

runoff from impervious surfaces. Permits are required 

for new development and redevelopment projects that 

will include more than 1 acre of impervious surfaces after 

construction. The 2017 Vermont Stormwater Management 

Manual Rule sets forth the treatment standards that 

must be met and the approved methods for calculating 

treatment volume (Tv) credits for the suite of structural 

and nonstructural stormwater treatment practices (i.e., 

BMPs) used onsite (Vermont Agency of Natural Resources 

2017). Using the hydrologic condition method set forth 

in the manual, a suite of practices must be implemented 

to achieve the “hydrologic condition volume,” which is 

calculated as the difference between the pre- and postdevelopment site runoff for the 1-year, 24-hour storm. 

The three types of State tree credits established under 

the reforestation nonstructural practice are summarized 

as follows:

1. Active reforestation involves planting a stand or 

block of trees, or individual trees, at a project site 

with the explicit goal of establishing a mature forest 

canopy or distributed cover that will intercept rainfall, increase evapotranspiration rates, and enhance 

soil infiltration rates.

Tv credit = 0.1 inches x reforested area (i.e., 1 acre of 

reforested area = Tv credit of 363 cubic feet)

2. Passive reforestation consists of protecting a portion 

of a project site from mowing and allowing native 

vegetation to reestablish.

Tv credit = 0.05 inches x practice area 

3. Single tree planting involves planting individual 

trees on a project site.

Tv credit = 5 cubic feet per tree planted (Box 1)

How the credits work—local credits

Many smaller scale development and redevelopment 

projects do not meet the greater than 1-acre impervious 

surface threshold, and thus do not require a State permit 

or involve the standard treatment practice requirements 

and credits described above. Because these smaller 

projects are governed by local ordinances, the Vermont 

League of Cities and Towns worked with State agencies 

and stakeholders to develop a Green Infrastructure 

Toolkit for local use. The Toolkit features:

» GSI Sizing Tool spreadsheet.

» Set of GSI fact sheets covering credits and criteria for 

10 stormwater practices, including trees.

» Low Impact Development and Green Stormwater 

Infrastructure Bylaw Template (i.e., model ordinance) that can be used or adapted into local policy.

The crediting approach for retained and newly planted 

trees is based on an impervious area reduction credit, 

which in effect reduces the total volume of runoff that 

needs to be treated through other practices (Box 2). Box 3

shows how the credits are calculated. 

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Box 1 Requirements for State Credits

Excerpts from the 2017 Vermont Stormwater 

Management Manual Rule:

REFORESTATION CREDITS

» The minimum contiguous area of active or passive 

reforestation shall be 2,500 square feet.

» The minimum width for reforested areas shall be 

25 feet. 

» The entire reforestation area shall be covered with 

an approved native seed mix covered with mulch 

to help retain moisture and provide a beneficial 

environment for the reforestation. 

» Active and passive reforestation areas shall not be 

maintained as landscaped areas. Forest leaf litter, 

duff, and volunteer sapling and understory growth 

shall not be removed.

» The manual lists additional requirements regarding 

tree species selection, soil, slope limitations, 

planting plans, protection from development, and 

other design issues.

SINGLE TREE CREDIT

» Trees planted for the single tree credit shall be at 

least 2 inches in diameter at breast height (dbh) for 

deciduous trees, or at least 6 feet tall for conifers. 

For full details on the State credits, see the 2017 

Vermont Stormwater Management Manual, Section 4.2.1 

(Vermont Agency of Natural Resources 2017). 
Box 2 Requirements for Local Credits

The Green Infrastructure Toolkit lists a number of 

requirements for credit, such as:

» The tree(s) must be on the development site and 

within 20 feet of new and/or replaced groundlevel impervious surfaces (e.g., driveway, patio, or 

parking lot).

» Trees must be retained, maintained, and protected 

on the site after construction and for the life of the 

development, or until any approved redevelopment 

occurs.

» Trees that are removed or die must be replaced 

with like species during the next planting season.

» See additional criteria regarding soil quality and 

volume and other design requirements.

RETAINED TREES

» Retained trees must be a minimum of 6 inches 

dbh. For trees smaller than this size that are 

retained, the newly planted tree credit may be 

applied instead.

» See additional guidelines for retained trees.

NEWLY PLANTED TREES

» New deciduous trees must be at least 1.5 inches 

diameter, measured 6 inches above the ground. 

New evergreen trees must be at least 4 feet tall.

» See additional tree selection, spacing, planting, and 

maintenance requirements.

For full details, see Fact Sheet #3 (Vermont League of 

Cities and Towns 2015).

BOX 3 Credit Calculation

How tree credits are calculated using Vermont’s GSI Simplified 

Sizing Tool:

BMP Tree Type Impervious Area Reduction Credit

Retained 

Tree

Evergreen

Deciduous

20% canopy area (min. 100 ft2 / tree)

10% canopy area (min. 50 ft2 / tree)

Newly 

Planted 

Tree

Evergreen

Deciduous

50 ft2 / tree

50 ft2 / tree

TOTAL GROUND LEVEL IMPERVIOUS COVER: ________ sq. ft.

RETAINED TREES:

Total evergreen canopy area: _________ sq. ft.

Evergreen canopy area  0.2 = _________ sq. ft. credit (min. 

100)

Total deciduous canopy area: _________ sq. ft.

Deciduous canopy area  0.1 = _________ sq. ft. credit (min. 50)

NEWLY PLANTED TREES:

Total new evergreen trees meeting requirements: _________

# of new evergreen trees  50 = _________ sq. ft. credit (min. 50)

Total new deciduous trees meeting requirements: _________

# of new deciduous trees  50 = _________ sq. ft. credit (min. 50)

TOTAL CREDIT: __________ sq. ft. 

(Max 25% of proposed impervious cover)

Source: GSI Simplified Sizing Tool Fact Sheet #3 (Vermont League of Cities and 

Towns 2015).

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References

Moore, J.; Macrellis, A.; Bailey, K. 2014b. Tree credits systems and incentives at the site scale. Montpelier, VT: Stone 

Environmental, Inc. 24 p. https://vtcommunityforestry.

org/sites/default/files/pictures/site_scale_tree_credits_2014_02_28_final.pdf. (12 November 2018). 

Moore, T; Barden, C; Galgamuwa, P.; Nooraei, A. [In 

press]. Predicting urban tree contributions to urban runoff 

budgets with statistical models. [Fact sheet]. Alexandria, 

VA: The Water Research Foundation.

Vermont Agency of Natural Resources. 2017. Vermont 

Stormwater Management Manual Rule. Montpelier 

VT: Vermont Agency of Natural Resources. 113 p. 

https://dec.vermont.gov/sites/dec/files/documents/

VermontStormwaterManagementManualRule_

Ch36_2017_Final_2016-12-20.pdf. (14 November 2018).

Vermont League of Cities and Towns. 2017. Green stormwater infrastructure toolkit. Montpelier, VT. https://www.

vlct.org/resource/green-stormwater-infrastructuretoolkit. (14 November 2018).

Vermont League of Cities and Towns. 2015. Vermont green 

stormwater infrastructure (GSI) simplified sizing tool for 

small projects fact sheets. Montpelier, VT. https://www.

vlct.org/sites/default/files/documents/Resource/2015_

GSI-Simplified-Sizing-Tool-Fact-Sheets.pdf. (14 November 

2018).

For more information on crediting trees in the context of stormwater management, refer to the 

suite of resources developed by the Center for Watershed Protection on Making Urban Trees Count. 

Adapted from: U.S. Department of Agriculture, Forest Service. 2020. Urban forest systems 

and green stormwater infrastructure. FS-1146. Washington, DC. 23 p.

https://www.fs.usda.gov/sites/default/files/fs_media/fs_document/Urban-Forest-Systems-GSI-FS-1146.pdf

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