2 KudoZ points awarded for this answer. Comment: "Gabrielle's support for the whole "core" idea gave me the confidence to go with the idea of a "noyau de biodiversité" described here: http://developpementdurable.revues.org/document1754.html La trame verte a pour vocation de créer une base de concertation à partir d’un dispositif régional environnemental, dont l’objectif est le maintien d’espaces dédiés à la biodiversité. Cette réflexion est développée autour des notions de « cœurs de nature » (ou « noyau de biodiversité ») remarquables par la présence d’espèces faunistiques et floristiques exceptionnels et de « corridors écologiques » devant favoriser la biodiversité aux échelles régionale et européenne. The following definition of a "biodiversity hub" seems to fit in nicely with the description of a "coeur de biodiversité" given in the link posted by Rachel: http://www.wcs.org/media/file/CHBP_lo-res.pdf Biodiversity hub—These ecological units serve as potential “source” habitats, meaning that biodiversity within them can help to replenish the biodiversity of nearby “sink” habitats. Therefore, if connectivity with other habitats is maintained these hubs may help to sustain biodiversity outside of their borders, throughout the Croton-to-Highlands towns. Key properties of a biodiversity hub include (1) adequate acreage (at least 1,000 acres) to support species that require large expanses of habitat; (2) relatively high quality, non-degraded habitat conditions; and (3) linkages to other landscape units, enabling movement among them (dispersal, migration). Hence my choice of "biodiversity hubs". Many thanks to all who helped me reach this answer."