HUC6 terrestrial core tiers is one of the principal landscape conservation design (LCD) products, and it is best understood in the context of the full LCD process described in detail in the technical document on landscape design (McGarigal et al 2017). This particular product was initially developed for the Connecticut River watershed as part of the Connect the Connecticut project (www.connecttheconnecticut.org) — a collaborative partnership under the auspices of the North Atlantic Landscape Conservation Cooperative (NALCC), and subsequently developed for the entire Northeast region as part of the Nature's Network project (www.naturesnetwork.org). HUC6 terrestrial core tiers represents a two-tiered, spatially-nested hierarchy of terrestrial core areas and supporting landscapes. These tiers in combination with the HUC6 terrestrial core-connector network (see terrestrial core area network document, McGarigal et al 2017) and the aquatic core areas (see aquatic core areas document, McGarigal et al 2017) spatially represent a tiered ecological network for the Northeast region. This ecological network is designed to provide strategic guidance for conserving natural areas, and the fish, wildlife, and other components of biodiversity that they support within the Northeast.
McGarigal, Kevin; Compton, Brad; Plunkett, Ethan; DeLuca, Bill; and Grand, Joanna, "Designing Sustainable Landscapes: HUC6 Core Tiers" (2018). Data and Datasets. 49.