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Tree Ordinance Guidelines
Concepts: Mitigating for tree loss
Overview of mitigation tactics
Mitigation measures
Mitigation location
Use of in-lieu fees
Recommendations
Overview of mitigation tactics
Provisions that seek to protect either individual trees (provisions 30, 31)
or stands of trees (provision 32) normally require mitigation as a condition
for approving destruction of, or damage to, tree or woodland/forest resources.
Essentially all mitigation is based on the following two measures:
1. Protect existing
trees or woodland/forest resources
2. .Plant
new trees (this may include more general restoration
of woodland/forest ecosystems)
Relative to the parcel or project area where tree removal occurs, mitigation
measures can be implemented at one or both of the following locations:
A. On site
B. Off site
The basic mitigation measures and locations give rise to the four combinations
shown in the following table. Almost all mitigation tactics can be grouped into
one of these four categories. Although simple in concept, these four basic mitigation
tactics can be implemented in a wide variety of ways, each of which have different
consequences for the community forest. Some of the most common examples of each
mitigation tactic are listed in the table below.
| Mitigation measures and locations |
1. Protect existing trees or stands |
2. Plant new trees and/or woodland/forest
restoration |
| A. On site |
• Protect existing individual trees and/or stands through project
design:
- relocate structures or infrastructure
- utilize specialized construction methods to minimize damage to tree
roots
- set aside portions of project area as woodland/forest preserves
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• Plant new trees in landscaped portions of parcel to replace those
removed
• Plant new trees on portions of the project area set aside as woodland/forest
preserves
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| B. Off site |
• Purchase land with existing trees or stands by public agency or
land trust and set aside as permanent woodland/forest preserves
• Establish permanent conservation easements on individual trees
or stands on private lands to protect those tree resources from removal.
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• Plant new trees on approved public lands
- landscaped areas
- rehabilitation and reforestation of degraded natural woodlands / forests
- afforestation of lands that currently lack trees (usually former woodlands/forests)
• Plant new trees on approved private lands
- land trust holdings
- privately-owned woodland/forest preserves protected with conservation
easements
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Many ordinances allow for more than one form of mitigation. The permitting
authority selects and approves the specific option or combination of options
that mitigate appropriately for the impacts of a given project. In some cases,
a community can establish a general prioritization of possible mitigation tactics
(e.g., protection preferred over planting, on site preferred over off site).
However, because the constraints and opportunities provided by each situation
can differ, the permitting authority should have some flexibility in prioritizing
mitigation tactics.
Mitigation measures
Each mitigation measure (protection or planting) has advantages and disadvantages
with respect to various management objectives, as shown in the following table.
| Management
objective |
1. Protect existing
trees or stands
|
2. Plant new trees
or woodland/forest restoration
|
| 1.
Prevent net loss of tree canopy or forest type |
If some trees are
protected as a condition for removing other trees, net loss of canopy or
forest type always occurs over the short term. If mitigation trees are mature,
additional long term canopy loss is possible when the mitigation trees die.
The degree of loss is a function of the mitigation ratio (e.g., 1 for 1
mitigation could lead to 50% loss). |
Over the short term, canopy is normally reduced. Planting or afforestation
has the potential to prevent long-term net loss if:
(a) mitigation ratio is at least 1 successful new tree for
each tree removed;
(b) replacement species have similar mature canopy spread;
(c) replanting or natural regeneration maintains the mitigation
planting in perpetuity
|
| 2. Maintain
mature tree canopy |
Some mature canopy
can be maintained over the short term. Long term maintenance depends on
whether provisions have been made for natural regeneration and/or eventual
replanting. |
Loss of mature canopy
is not mitigated over the short term (i.e., not until new plantings mature). |
| 3. Maintain aesthetics
associated with existing trees |
Aesthetic impacts
associated with loss of mature trees can be partially mitigated, depending
on location of mitigation trees. |
Aesthetic impacts
associated with loss of mature trees are not mitigated over the short term. |
| 4. Maintain habitat
values |
Habitat values associated
with mature trees and existing woodlands/forests may be partially mitigated
over the short term, depending on:
(a) habitat elements provided by mitigation trees;
(b) the location of the mitigation trees with respect to other trees
or habitat elements;
(c) level of disturbance (both initial and ongoing) in the mitigation
area |
Loss of habitat values
associated with mature trees and existing woodlands/forests are not mitigated
over the short term. New plantings do have habitat values, but these typically
differ from those associated with mature trees and stands. |
| 5. Maintain species
diversity |
The degree of mitigation
provided depends on the species composition of protected areas. Locally
uncommon or rare tree species can be conserved at least over the short term.
Diversity of species other than trees (e.g., understory plants, animals)
may also be conserved. |
Depending on species
used in planting, tree species diversity can be increased or decreased relative
to preexisting tree or woodland/forest resources. The level of diversity
among non-tree species depends strongly on the plant community and restoration
/ management practices used. Undesirable nonnative "weedy" species
may be more prevalent in new plantings compared to existing woodlands/forests..
|
| 6.
Maintain age diversity |
Age diversity
can be maintained if a variety of age classes are represented in the protected
trees and stands. |
Age diversity
of forest or stand is usually reduced. Plantings typically give rise to
even-aged stands. |
| 7.
Conserve local tree genetic resources |
Conservation of germplasm
from local tree populations and populations of other woodland/forest organisms
is possible if a sufficient number of individuals are protected. However,
maintaining a few widely scattered individuals of outcrossing wind-pollinated
species (e.g., many oaks) might not permit seed set and would effectively
eliminate regeneration. |
Local genetic resources
may be conserved if seed or other propagules from local populations are
used. Use of non-local planting stock in woodland/forest plantings may be
a source of "genetic pollution" and may accelerate the loss of
genetic traits associated with local adaptation. |
For plantings, several additional factors must be considered, as summarized
below.
|
Factor
|
Options
|
Comments
|
| Planting date |
During or after construction of applicant's project |
Delaying the planting relative to the applicant's project
activities may allow for better seasonal timing of the planting. However,
it may be useful to set a time limit (e.g., within 1 year after applicant's
project is completed) to avoid developing a backlog of unplanted trees. |
| Selection / purchase of planting stock |
City / county, contractor, or applicant |
Applicant fees may be collected by the city/county to purchase
planting stock, or applicant may buy stock directly. The city/county should
set and enforce strict standards for planting stock quality. |
| Installation |
City / county, contractor, or applicant |
Installation by the city/county or its contractors is funded
from applicant fees. Plantings by the applicant or contractors should be
subject to strict standards, monitored, and bonded for performance to ensure
quality. |
Mitigation location
Many management objectives can be met equally well with on-site and off-site
mitigation. However, the location of the mitigation has an impact on several
management objectives as noted below.
|
Management objective
|
A. On site
|
B. Off site
|
| 1. Mitigate for
local effects of tree removal |
Local
effects of tree loss can be at least partially mitigated. |
Local
effects of tree loss may not be mitigated if receiver site is distant from
the site of tree removal. |
| 2. Maintain habitat
value |
Ability to maintain
contiguous stands that conserve habitat value may be severely limited, especially
on small parcels. Level of disturbance may also degrade habitat value. |
More opportunities
may exist to maintain stands that are large, contiguous with other stands,
and relatively undisturbed, thereby maximizing habitat value. |
| 3. Conserve local
tree genetic resources |
Conservation of germplasm
from local tree populations and populations of other woodland/forest organisms
is possible. |
Local genetic resources
may not be conserved if the receiver site is distant from the site of tree
removal. |
Several other issues that should be considered when choosing between on-site
and off-site mitigation are summarized below.
|
Issue
|
A. On site
|
B. Off site
|
| Area
and/or tree resources available for mitigation |
May be limited, especially
in small parcels or for projects that occupy a large proportion of the parcel. |
Generally
not limiting, but availability of potential mitigation sites close to the
project site may be limited. |
| Location
of mitigation area |
Relatively few options
for location, especially on small project sites. |
Potentially
more flexibility on location of mitigation area, but depends on the availability
of suitable public or private receiver sites. |
| Ownership
of mitigation area |
Normally owned by
applicant. Applicant may be required to dedicate the mitigation area or
a conservation easement on the area to the city / county, other public agency,
or a land trust. |
Normally
not owned by the applicant. Mitigation area is usually owned by a the city
/ county, a government agency (e.g., state parks), or a land trust. Privately-owned
mitigation areas are possible if the receiver sites are protected with permanent
conservation easements. |
| Maintenance
responsibilities |
Applicant typically
maintains trees if they retain ownership of mitigation area. City / county
has monitoring and enforcement responsibilities to ensure that tree resources
are maintained. If dedication of mitigation areas is required, local government
or land trust maintains trees. |
Mitigation
site landowner, who is generally not the applicant, maintains trees. City
/ county has monitoring and enforcement responsibilities to ensure that
tree resources are maintained. |
| In-lieu fees |
Generally not necessary. |
Commonly used. |
Use of in-lieu fees
When off-site mitigation is required, many jurisdictions allow the applicant
to pay fees to the local government in lieu of completing the actual off-site
mitigation. In many jurisdictions, in-lieu fees are the only option provided
for off-site mitigation. In most cities and counties in-lieu fees are deposited
into a dedicated account which is used for tree planting and maintenance and/or
the acquisition of woodlands/forests through direct purchase or the purchase
of conservation easements. Such accounts are sometimes referred to as "tree
banks".
The main advantage of using in-lieu fees is the relative simplicity of this
approach. Rather than requiring each applicant to negotiate for off-site land
purchases or conservation easements, the local government handles all of the
off-site mitigation arrangements. Consequently, the local government must have
the organizational structure necessary to ensure that mitigation trees are planted
and will survive over the long term, and/or that reserves on public or private
lands are managed to perpetually sustain forest resources. Fees that are collected
must be sufficient to pay for the direct and indirect costs associated with
the mitigation tree planting, maintenance, and monitoring programs.
Furthermore, if trees planted or preserved as mitigation are to be maintained
in perpetuity to offset tree loss, sufficient reserves must be available to
establish an endowment to pay for eventual replanting. If in-lieu fees only
support a single generation of trees and natural regeneration is not a possibility
on the receiver site, net canopy loss will occur over the long term. This is
especially the case for trees planted in horticultural situations (e.g., roadsides
or parks), which typically have a relatively short life span.
A related problem is that in-lieu fees should be specifically restricted to
additional mitigation plantings that are above and beyond the community's regular
planting programs. If in-lieu fees are used only as a replacement for tree planting
previously supported by the local government's general fund, the total amount
of funds available for tree planting might actually be reduced, and public tree
planting would be insufficient to mitigate for tree loss in both public and
private lands.
Recommendations
1. Allow for the full range of mitigation options (on and off site, protection
and planting, in-lieu fees) to provide flexibility to deal with a range of
different permit situations.
2. Permitting authority should have the option to select and/or approve appropriate
mitigation options (including a combination of tactics) based on the local
government's management goals and priorities, and the particular circumstances
of each project.
3. Trees or woodland/forest resources maintained by the applicant will need
to be monitored by the local government to ensure and enforce compliance.
The ordinance should expressly provide this authority.
4. Fees charged should be sufficient to provide for ongoing monitoring and
maintenance, including eventual replanting. If direct mitigation by applicant
is allowed, additional fees may be necessary to provide for monitoring, maintenance,
and enforcement.
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