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
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
|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.
Plant new trees on approved public lands
Plant new trees on approved private lands
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.
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:
|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.
|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.|
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.|
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.
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.