University of Massachusetts Amherst

Conservation Assessment and Prioritization System

Conservation Assessment and Prioritization System

The Critical Linkages Project

Critical Linkages is a set of comprehensive analyses of opportunities for restoring connectivity by upgrading or removing infrastructure. Initiated in 2010, with support from The Nature Conservancy, the initial phase assessed each road stream crossing and dam in Massachusetts for the potential to restore aquatic connectivity by upgrading culverts and removing dams. An additional analysis assessed road segments throughout the state potential improvements in connectivity to be gained by installing road passage structures. A second phase of the project assessed potential longer-distance improvements in regional connectivity improvements from installing road passage structures. The road-stream crossing and dam analyses have been updated regularly as new data become available, and have been applied to 13 states in the Northeast as part of Designing Sustainable Landscapes.

We employ a “coarse-filter” approach in our assessment of connectivity; one that does not involve any particular focal species but instead holistically considers ecological systems. Because we were dealing with biodiversity in its broadest sense we distinguished two important scales for assessing connectivity, which we refer to as local and regional scales. Local connectivity refers to the spatial scale at which the dominant organisms interact directly with the landscape via demographic processes such as dispersal and home range movements. Regional connectivity refers to the spatial scale exceeding that in which organisms directly interact with the landscape. This is the scale at which long-term ecological processes such as range expansion/contraction and gene flow occur. Phase I of the Critical Linkages project focused on analyses of local scale connectivity while phase II focuses on assessing connectivity at the regional scale.

Phase I

Phase I of the Critical Linkages project built on the existing Conservation Assessment and Prioritization System (CAPS), a computer model that incorporates biophysical and anthropogenic data to compute an index of ecological integrity (IEI). Because CAPS provides a quantitative assessment for IEI as well as each metric used in ecological integrity models it can be used for comparing various scenarios. Scenario analysis involves running CAPS separately for each scenario, and comparing results to determine the loss (or gain) in IEI or specific metric units.

In Phase I of the Critical Linkages project we used the scenario testing capabilities of CAPS to assess changes in the connectedness and aquatic connectedness metrics for dam removal, culvert/bridge replacement projects and construction of wildlife passage structures on roads and highways. The connectedness metric is a measure of the degree to which a focal cell is interconnected with other cells in the landscape that are a potential source of individuals or materials that contribute to the long-term ecological integrity of the focal cell. Connectedness is based on a “resistant kernel,” introduced by Compton et al. (2007), which is a hybrid between two existing approaches: the standard kernel estimator and least-cost paths based on resistant surfaces.

North Shore connectedness

Connectedness metric for an area on the north shore of Massachusetts. Areas in darker colors are more interconnected with similar areas nearby than those depicted in lighter colors. White areas are developed land.

Aquatic connectedness functions much like connectedness but is constrained to move only along the centerlines of streams, rivers, water bodies and wetlands.

North shore aquatic connectedness

Aquatic connectedness metric for an area on the north shore of Massachusetts. This metric is applied only to wetland and aquatic communities. Areas in darker blue are more interconnected with similar areas nearby than those depicted in lighter color.

A baseline assessment of connectedness and aquatic connectedness provides a statewide base scenario for comparison of restoration options. Scenario-testing software was developed to efficiently assess restoration potential for large numbers of possible restoration projects and then applied statewide to dams, road-stream crossings and road/highway segments. Results of these analyses indicate that a relatively small proportion of culvert replacements or dam removals would result in substantial improvements in aquatic connectivity.

delta crossings colors

Results of culvert/bridge replacement scenario analyses for a portion of Massachusetts. Size of the circles is proportional to the change in aquatic connectedness that would be achieved by crossing replacement. The larger the circles the greater the improvement in aquatic connectedness.

linkages road with topo

Results of wildlife passage structure scenario analyses for a portion of Massachusetts. The color of the lines is proportional to the change in connectedness that would be achieved by the construction of a wildlife passage structure. The darker the color the greater the benefit of using a passage structure at that location.

Critical Linkages for Cold Water Streams

A special application of Critical Linkages focusing on cold water streams was developed and implemented as part of a project funded by a USFWS Hurricane Sandy Recovery and Mitigation grant. In this analysis cold water streams defined by various mean summer temperature thresholds (16°C, 18°C, 20°C and 22°C) were identified using The Nature Conservancy’s stream temperature data (see Stream Temperature settings variable, McGarigal et al. 2017). For each temperature threshold, Critical Linkages was used to evaluate crossings and calculate the effect of crossing upgrades or replacements on aquatic connectivity for cold water streams. Effect is calculated as the change in aquatic connectedness for cold water stream reaches multiplied by the IEI values for those stream reaches. All crossings were included in the analyses because it is conceivable that a stream reach that does not meet the definition of cold water (based on chosen temperature thresholds) might still be important for linking together various cold water stream reaches, though crossings far from coldwater streams (where delta = 0) were dropped from the analysis. A separate shapefile is available for each of the four temperature thresholds.

Data and Documentation

Critical Linkages has been rerun for road-stream crossings and dams several times since the initial completion of this project, both for Massachusetts as part of the CAPS project, and for 13 states in the Northeast as part of Designing Sustainable Landscapes (umassdsl.org). As more data from crossing surveys coordinated by the North Atlantic Aquatic Connectivity Collaborative (NAACC) become available, the Critical Linkages analyses become more reliable. The current Critical Linkages report applies to the most recent updates of Critical Linkages for both Massachusetts (Massachusetts CAPS) and the Northeast (Designing Sustainable Landscapes):

DSL_documentation_critical_linkages.pdf

Use links in the report or below to download results of Critical Linkages Phase I analyses for Massachusetts.

The original Critical Linkages final report is available for the detail it provides, but included links are no longer active, as the original results have been superseded by more recent runs.

Legacy document: Critical-Linkages-Phase-1-Report-Final.pdf

Phase II

In Phase II of the project we used a hybrid of the resistant kernel estimator approach (used in phase I) and a graph theoretic approach to assess connectivity at a regional scale. We created a hybrid system that maintained the spatial realism of the resistant kernel estimator approach and capitalized on the computational efficiencies of the graph matrix representation. Results of the phase II regional-scale analysis for Massachusetts are available in the final report for the project:

Critical-Linkages-Phase-II-Report.pdf

Although Critical Linkages II has not been updated since its original completion in 2013, its approach provided the foundation for assessing regional connectivity in Nature’s Network, as well as recent and ongoing connectivity projects.

Critical Linkages Phase I Results

Critical linkages results for Massachusetts (based on data downloaded from NAACC on October 19, 2023) are available in the following shapefiles:

Road-stream crossings (updated December 7, 2023):

https://landeco.umass.edu/web/masscaps/cl_crossings.zip

Coldwater road-stream crossings (contains 4 shapefiles, one for each temperature threshold of 16 C, 18 C, 20 C, and 22 C; updated December 7, 2023):

https://landeco.umass.edu/web/masscaps/cl_coldwater.zip

Dams (updated December 7, 2023):

https://landeco.umass.edu/web/masscaps/cl_dams.zip

Culvert upgrades shapefile — Point shapefile including the attributes listed below for each road-stream crossing. The most commonly-used fields are in boldface.

Field Description
FID, shape Fields used internally by GIS software.
id A unique numeric crossing ID.
crosscode For surveyed crossings (and some unsurveyed crossings), the crossing code used in the NAACC database.
survey_id The unique ID of the NAACC survey (for surveyed crossings only).
x_coord, y_coord The coordinates of the crossing after it has been moved to an appropriate raster cell.
moved 1 = the crossing did not need to be moved; 2 = the crossing was moved from the original to an adjacent cell to ensure it falls on a road-stream crossing in our data.
oldx, oldy The original vector based coordinates of the crossing.
surveyed 1 if the aquatic crossing score is based on a survey, 0 if not.
database The source database for surveyed road-stream crossings.
group Group ID for grouped crossings (multiple nearby crossings when a stream crosses a divided highway).
groupsize Number of crossing in group.
bridge 0 = non-bridge; 1 = bridge (based on NAACC surveys for surveyed crossings; modeled otherwise)
bridgeprob The modeled probability that the crossing is a bridge.
bsurveyed 1 if the bridge status is based on a survey, 0 if not.
no_cross For surveyed crossings this is 1 if the location is not actually a crossing even though it was predicted to be one by intersection of roads and streams GIS data.
aquatic The aquatic passability score (modeled or directly from NAACC surveys), ranging from 0 to 1 with higher values being more passable.
aquaLCI, aquaUCI The lower and upper confidence interval on the aquatic score.
base The sum of aquatic connectedness in the neighborhood of the focal road-stream crossing for the current condition (i.e., before culvert upgrade).
alt The sum of aquatic connectedness in the neighborhood of the focal road-stream crossing for the altered condition (i.e., after culvert upgrade).
delta The difference between the altered and base aquatic connectedness, multiplied by 1000 to make the numbers more tractable. This represents the potential improvement in aquatic connectedness from upgrading the crossing.
effect The restoration potential index, defined as IEI × delta, representing the potential improvement in local aquatic connectedness weighted by IEI (Index of Ecological Integrity). Note that as of 2021, effect uses a version of IEI that omits aquatic connectedness in order to avoid depressing scores for crossings that have low aquatic connectedness due to stream crossings.
effectln The logarithm of effect, for display on maps.
loss Log-transformed delta, rescaled from 0-1.
restore Log-transformed effect, rescaled from 0-1.
rank Rank of effect. Lower numbers indicate higher restoration potential.
percentile Percentile of effect.
ADT The estimated average daily traffic rate over the crossing structure.
roadclass The road or train class associated with the crossing.

Dam removals shapefile — Point shapefile including the attributes listed below for each dam.

Field Description
FID, shape Fields used internally by GIS software.
dsl_id A unique ID for each dam, based on neac_id. When duplicate dam points were added to cover multiple flowlines existing an impoundment, a letter was appended, e.g., “MA_MA00068_a.”
x_coord,
y_coord The coordinates of the dam after it has been moved to an appropriate raster cell.
height The Structural height of dam (m), from the NEAC “height” field. Missing values and zeros were replaced with 5.5 m, the mean dam height in the Northeast.
base The sum of aquatic connectedness in the neighborhood of the focal dam for the current condition (i.e., before dam removal).
alt The sum of aquatic connectedness in the neighborhood of the focal dam for the altered condition (i.e., dam removal).
delta The difference between the altered and base aquatic connectedness, multiplied by 1000 to make the numbers more tractable. This represents the potential improvement in aquatic connectedness from removing the dam.
effect The restoration potential index, defined as IEI × delta, representing the potential improvement in local aquatic connectedness weighted by IEI (Index of Ecological Integrity).
effectln The logarithm of effect, for display on maps.
loss Log-transformed delta, rescaled from 0-1.
restore Log-transformed effect, rescaled from 0-1.
rank Rank of effect. Lower numbers indicate higher restoration potential.
percentile Percentile of effect.

The Critical Linkages project was funded by and The Nature Conservancy and the Federal Highway Administration via a contract with the Massachusetts Department of Transportation. Information on this web site was prepared in cooperation with the Massachusetts Department of Transportation Office of Transportation Planning and the United States Department of Transportation, Federal Highway Administration. The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official view or policies of the Massachusetts Department of Transportation or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation.