Terrestrial and Wetland Core-Connector Network, Northeast U.S.

Apr 26, 2017 (Last modified Jul 13, 2017)
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The Terrestrial Core-connector Network is one of a suite of products from the Nature’s Network project (naturesnetwork.org). Nature’s Network is a collaborative effort to identify shared priorities for conservation in the Northeast, considering the value of fish and wildlife species and the natural areas they inhabit. This product consists of two components: core areas and connectors. A number of additional datasets that augment or complement the Core-connector Network, including road-bounded natural blocks that surround the cores areas and a set of grassland bird core areas, are available in the Nature’s Network gallery: https://nalcc.databasin.org/galleries/8f4dfe780c444634a45ee4acc930a055.

Terrestrial and wetland core areas are intact, well-connected places that, if protected, will support a diversity of fish, wildlife, and plants, and the ecosystems they depend upon. Each core area contains important or unique features, including intact, resilient examples of each major ecosystem type in the Northeast and Mid-Atlantic. Core areas contain widespread ecosystems, such as hardwood forests, rare natural communities, such as bogs, and important habitat for a variety of fish, wildlife, and plants. By design, they encompass approximately 25% of the landscape of the region.

Core areas are linked together by a network of connectors. The connectors are designed to enable the movement of animals and plants between core areas and across the landscape into the future. A detailed technical guide to the Terrestrial Core-connector Network is available at: http://jamba.provost.ads.umass.edu/web/lcc/DSL_documentation_tCoreNet.pdf.

Core areas are also embedded within road-bounded natural blocks. These blocks are natural areas that surround and help support the integrity of core areas. They maintain ecological processes and foster the movement of animals and plants across the landscape. By following the boundaries between natural and developed areas, they also provide practical units for conservation action.

This set of products also includes a network of core areas for grassland birds. They are intended to represent the most suitable breeding areas for grassland birds, consisting of large and intact grasslands, pastures and hayfields, as of the time of the analysis. Due to their unique association with habitat that has been created and maintained for human use, grassland birds are treated separately from wildlife that use habitat such as forests and wetlands, which are not as dependent on intensive management. Grassland bird core areas therefore represent an important complement to terrestrial and wetland core areas.  A detailed technical guide to grassland bird core areas is available at: http://jamba.provost.ads.umass.edu/web/lcc/DSL_documentation_grasslandCores.pdf.

Together with aquatic core areas and buffers, the terrestrial core areas and connectors provide the primary network of resilient and ecologically intact habitats that will support biodiversity under changing conditions in the Northeast and Mid-Atlantic region.  These areas represent a “coarse-filter” approach to biodiversity conservation and provide strategic guidance for conserving natural areas and the fish and wildlife that they support. They are complemented by the “fine-filter” approach of the Habitat Importance Condition for Imperiled Species.

Intended Uses:

  • Identify the best places to begin land and water protection
  • Sustain natural resources on private lands by promoting stewardship with private landowners
  • Inform strategic acquisition of parcels by public or nonprofit organizations
  • Set local conservation priorities with a regional perspective
  • Protect biodiversity by understanding the ecological importance of individual areas
  • Identify important natural areas vulnerable to future development
  • Determine which areas in the network remain unsecured from development
The Terrestrial Core-connector Network can serve as a starting point for a regional conservation network that can be used in combination with other sources of information to direct action. You might explore it in combination with:
  • Other data layers to identify additional areas of high ecological value. Layers to consider include: 1) aquatic cores and buffers, 2) index of ecological integrity, 3) The Nature Conservancy's (TNC) terrestrial resiliency index, 4) individual species landscape capability indices, and 5) habitat condition for imperiled species. 
  • The secured lands layer to identify the places in the network that remain unsecured from development, and thus could represent priorities for land protection.
  • The probability of development layer and regional vulnerability layers to identify places in the Core-connector Network that are relatively vulnerable to future development, and thus could represent priorities for land protection.
  • Resource priorities identified at the state or local level, but that are not available across the entire region (e.g., from State Wildlife Action Plans, towns, and land trusts), to further rank areas for land protection.

Description and Derivation

The Core-connector Network is based on GIS analyses designed to assess the physical and biological value of resources across the Northeast and Mid-Atlantic, and to identify the most important places and connections for them. Core areas integrate four components:

High integrity examples of more than 90 terrestrial and wetland ecosystem types across the Northeast and Mid-Atlantic. Ecosystem locations have been mapped through a partnership of The Nature Conservancy and the Northeast state fish and wildlife agencies.  Their integrity has been assessed using the Index of Ecological Integrity developed by the University of Massachusetts Amherst.
Terrestrial sites assessed as having the greatest potential to be resilient over the long term, as identified by The Nature Conservancy.
Rare natural communities identified and mapped by state natural heritage programs.
High quality habitat for 27 terrestrial and wetland wildlife species carefully selected to represent the habitat needs of a large number of species that share many of the same habitats. These habitats have been mapped by UMass Amherst.

Core areas were built from focal areas (“seeds”) with high value based on one or more of the attributes listed above. These "seeds" were expanded to encompass surrounding areas that provide additional ecological value and resilience to both short- and long-term change. These surrounding areas are typically of high to moderate ecological value. To maintain a coherent shape and size, in some cases core areas contain low-intensity development and minor roads, but high-intensity development and major roads are excluded. Collectively, terrestrial core areas encompass 25% of the area of the region, as decided by the partnership. Core areas range in size from 3.6 to 107,996 ha, with an average size of 794 ha. The total number of disjunct core areas is 20,358, encompassing 16 million ha.

This version of terrestrial core areas is based on stratifying the ecosystem and species inputs by large watershed (HUC 6 level) such that core areas comprise 25% of the landscape of each watershed. This ensures that core areas are well-distributed and well-connected across the landscape. However, this also means that some of the highest quality examples of ecosystems and habitats from a regional perspective are not included in core areas, where their inclusion would otherwise result in more than 25% of the area of a watershed being assigned core areas. A complementary version of terrestrial core areas that is not stratified by watershed is also available as part of the Nature’s Network  package (naturesnetwork.org).
Core-to-core Connectors represent “corridors” that could facilitate the movement of plants and animals (i.e., ecological flow) between terrestrial core areas. These connectors increase the resiliency of the core area network to uncertain land use and climate changes. They are wider where more movement between cores is expected because of larger and closer core areas and a more favorable natural environment exists between them. Connectors primarily link adjoining core areas where there is the greatest similarity in ecosystems; they do not necessarily represent travel corridors for any individual species. Connectors may traverse through areas of low-density development and cross roads of all classes, but they do not include high-intensity development. Connectors are not identified between core areas that are greater than 10 km apart. Collectively, connectors encompass an additional ~17% of the Northeast area. Note: an additional connectivity component (Regional Flow, Anthropogenic Resistance (Simplified Categories), Eastern U.S. and Canada) is available in the Nature’s Network package which represents the permeability or connectivity of the landscape for animals and plants without regard to the location of the terrestrial core areas.

Road-bounded natural blocks are natural areas that contain any part of a terrestrial core area and that are bounded by roads, development, agriculture, barren land, and large open-water bodies.

Attribute Information and Field Definitions

The attributes listed below are available for each polygon (note, the connector polygons contain values for only the first four attributes listed below):
FID = ESRI assigned unique number for each polygon.

Shape = ESRI assigned feature type = “polygon.”

type = indicator designating the polygon as: “t1core” or “connector.”

coreID = connectors all have an ID of 1, each core has a unique ID > 1.

areaCount = size of the core area in number of cells (30 x 30 m); this includes any developed cells.

areaHa = size of the core area in hectares; this includes any developed area.

rareCom = percentage of the core comprised of S1-S3 rare communities as defined and mapped by the state Heritage Programs. 

system1, system2, system3 = The top three terrestrial or wetland ecological systems for which the core is particularly important. In other words, for these systems the cumulative ecological integrity of the system within the core is greater than expected (from a statistical perspective) given its distribution across the entire core area network. Note, the systems listed here reflect the systems for which the core is especially important, but are not necessarily the most abundant systems in the core.

species1, species2, species3 = The top three representative species for which the core is particularly important. In other words, for these species the cumulative landscape capability index within the core is greater than expected (from a statistical perspective) given its distribution across the entire core area network. Note, the species listed here reflect the species for which the core is especially important, but are not necessarily the species with the highest total landscape capability in the core.

ecoURL = contains links to the Ecosystem tables* for each core area.

sppURL = contains links to the Species tables* for each core area.

*The Ecosystem and Species tables contain additional detailed composition statistics, and more information about relative importance, for each core area. See the technical documentation for more information (http://jamba.provost.ads.umass.edu/web/lcc/DSL_documentation_tCoreNet.pdf).

Known Issues and Uncertainties

As with any project carried out across such a large area, the Terrestrial Core-connector Network is subject to limitations. The results by themselves are not a prescription for on-the-ground action; users are encouraged to verify, with field visits and site-specific knowledge, the value of any areas identified in the project. Known issues and uncertainties include the following:

  • The results do not incorporate important social, economic, or feasibility factors.
  • Users are cautioned against using the data on too small an area (for example, a small parcel of land), as the data may not be sufficiently accurate at that level of resolution.
  • The mapping of ecosystem locations and development is known to be imperfect, which consequently affects the mapped values for ecosystem integrity and species habitat. While the ecosystem mapping is anticipated to correctly reflect broad patterns of ecosystem occurrence, errors in classification and placement do occur, as with any regional GIS data. In addition, errors in mapping and alignment of development, roads, traffic rates, and a number of other data layers can affect the model results.
  • It is not possible to map all factors affecting ecosystem integrity and species habitat across the Northeast, and the omission of such factors can be anticipated to create pose some limitations in the results. An example is the limited ability to map the regional impact of invasive species.
  • Not all locations of rare natural communities have been mapped by states and therefore may not be components of core areas. The current version of core areas does not reflect rare natural community data from Rhode Island.
  • The habitat needs of the representative species used in the project do not fully reflect the habitat needs of all species with which they co-occur; some specialized habitats may be missed entirely.
  • The identification of core areas is predicated on the assumption that biodiversity is best supported by intact, well-connected landscapes. While this assumption is soundly grounded in conservation biology theory and findings, it is recognized that many species of conservation concern may depend on habitat currently existing in a less intact state or otherwise missed by core areas. The Core Habitat for Imperiled Species product, in particular, is intended to complement the core areas by focusing on such areas.
  • Because of the difficulty in distinguishing grasslands and pastures from other types of agricultural land using remote sensing, and because suitability to grassland birds can change relatively frequently with farmland abandonment or differing management regimes, caution is warranted in interpreting the accuracy and value of individual grassland bird core areas.
Data Provided By:
University of Massachusetts Amherst Landscape Ecology Lab
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University of Massachusetts Amherst
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Administration account for the Northeast Conservation Planning Atlas.