Below are a series of quick links to the information in the summary tables based on the solution type.
Table 3: Connectivity Solutions
Table 4: Patch Solutions
Tables 3 and 4 present a list of mitigation solutions developed from the interviews with transportation agencies, reports and literature. Table 3 lists mitigation solutions specific for connectivity, and Table 4 lists mitigation solutions specific for patch. Because the table reflects projects that, for the most part, have been constructed and have demonstrated effectiveness through monitoring, the solutions are considered to have immediacy of implementation, are cost-effective for specific situations, and have been accepted by resource agencies as mitigation measures. Each mitigation solution included has at least one project example.
The tables are organized by types of solutions. Table 3 lists solutions to address connectivity impacts and Table 4 lists solutions to mitigate for patch impacts. Within each table, the mitigation solutions are further listed by size of structure followed by the species group that it serves. Each solution is also supported by one or more project examples with the corresponding reference. Design considerations, mitigation cost and other relevant factors are included when available.
As described previously, the review and selection of potential mitigation solutions for habitat fragmentation should be preceded by an analysis of potential project impacts, or in the case of some reconstruction and rehabilitation projects, opportunities to restore connectivity due to past impacts. With an understanding of the type of fragmentation impact (connectivity or patch) and the target species that the mitigation solution should serve, practitioners can quickly find and review information pertaining to one or more mitigation options. Further evaluation to address the project-specific feasibility and effectiveness of any mitigation solution is required prior to advancing the mitigation solution into project design plans.
A brief description of the main components of the table and relevant information sources are provided below.
Type of Solution:
The tables are organized by the type of solution for either connectivity (Table 3) or patch (Table 4). As noted, the solutions represent mitigation solutions that have been implemented before and are supported by examples. For connectivity (Table 3) the solutions are organized into three general approaches: 1) Shift Alignment; 2) Install structure; and 3) Retrofit structure. Each addresses different approaches to facilitate wildlife passage. Under Install Structure further divisions are made to present more specific approaches based on type and size of structure.
In Table 4, Patch solutions are more direct, though fewer examples were identified by DOTs and in the literature. The list of solutions includes:
Project examples were not available for each of these approaches; however, some elements that represent avoidance and minimization measures are common practice and included though not specific examples or project information is available.
Species Group:
The wildlife species group or target species that may utilize or benefit from a solution is presented with the corresponding solution. This is perhaps the second most important consideration in evaluating suitable habitat fragmentation solutions for a project. Many of the solutions address a wide range of species, though project examples that discuss specific species are also presented. It should be noted that many species have specific behavioral traits that influence their use of a passage or overpass and the selected design needs to address these species-specific needs.
Region:
The region/State to which the approach or example project is suitable is provided. Most solutions can be applied throughout the nation to address common species such as deer, though certain species (i.e. cougars, moose) have well defined ranges that restrict the regions in which the solutions would be applied.
Mitigation Type:
The mitigation solution has been classified based on its anticipated type of mitigation, i.e. avoidance, minimization or compensation. In some circumstances, the solution can be a minimization or compensation action depending the location (on-site = minimization; off-site location = compensation).
Timing of Solution/Evaluation:
The evaluation and adoption of a solution can occur at different stages in the project development and this section suggests the appropriate timing to adopt a mitigation solution. Mitigation solutions that are avoidance and minimization approaches should be considered at the project planning stage, whereas compensation solutions can be considered at the project development/permitting stage. Exceptions occur such as efforts to identify advance mitigation opportunities for projects that are in keeping with the FHWA Ecological approach.
Impact Reduction Benefits:
This section summarizes some of the expected benefits of the mitigation solution that addresses habitat fragmentation impacts. Most connectivity solutions are expected to reduce wildlife-vehicle collisions and maintain biodiversity and genetic exchange within the target species population. While the expected effectiveness of the solution can be stated for WVC reduction based on on-going research, actual results are dependent upon site specific variables.
Cost Estimates for Mitigation Solutions:
This section presents available cost information for the construction of mitigation solutions. The values sometimes include maintenance cost. Through the interviews and literature search it was clear that data for design, construction and maintenance cost for mitigation solutions is not readily available. Only a few states have started tracking environmental mitigation costs for stormwater, noise abatement, wetlands and streams separately from construction costs. A survey of state tracking methods for environmental mitigation by Wisconsin DOT in 2008 revealed that several states had initiated programs to better track project investments in environmental mitigation (WisDOT and CTC Associates, 2008). Since 2003, Washington State DOT has conducted surveys of environmental mitigation costs for a sample of projects every three years (WSDOT 2009).
Huijser et al. (2009) used estimated construction and maintenance costs in 2007 dollars for 13 large ungulate mitigation measures to determine cost benefit values. This data utilized project construction and maintenance cost data summarized from various sources and was presented in Appendix I of their report. This data was incorporated into Table 3 for connectivity solutions. Other data was included as available.
Mitigation solutions for patch impacts due to habitat fragmentation were similarly lacking project specific cost information. Habitat enhancement and restoration cost information was derived from related wetland mitigation and other habitat improvements. These cost range widely depending upon the site location, land cost, type of restoration activity and many other factors. The cost of mitigating for wildlife habitat impacts was addressed by the Environmental Law Institute (ELI) in 2007 (ELI 2007) and served as a source for cost information for some measures.
ELI gathered cost information for wetland compensation projects that include preservation, enhancement, restoration, creation, in-lieu-fee programs and wetland bank credits from a variety of sources for a target year of 2003. ELI estimated average wetland compensation costs reported by Corps Districts ranged from a low of $15,000 to a high of $150,000 per acre in 2003 (ELI 2007). In-lieu-fee and wetland bank credit costs varied widely across the nation. In-lieu-fee costs ranged from a low of $3,000 to a high of $129,000 per a
Design Considerations:
This section presents information relevant for the design, placement and effectiveness of the mitigation solution obtained from the source information for the referenced project. This section is not expected to address all of the design considerations for the implementation of a mitigation solution.
Sources:
Information sources for the project examples are presented along with internet links to the papers or document referenced.