ecotone
n.— «An ecotone is a term from the field of ecology. It is a place where landscapes meet—like field with forest, or grassland with desert. The ecotone is an area of increased richness and diversity where the two communities commingle. Here too are creatures unique to the ecotone…the so-called ‘edge effect.’» —Ecotone: Writing About Place , 2003. (source: Double-Tongued Dictionary)