Ecosystem
The term ecosystem was first used in 1935 in a publication by British ecologist Arthur Tansley. Tansley devised the concept to draw attention to the importance of transfers of materials between organisms and their environment. He later refined the term, describing it as "The whole system, ... including not only the organism-complex, but also the whole complex of physical factors forming what we call the environment". Tansley regarded ecosystems not simply as natural units, but as "mental isolates". Tansley later defined the spatial extent of ecosystems using the term ecotope.
Ecological land classification
American geographer Robert Bailey defines a hierarchy of ecosystem units ranging from micro-ecosystems (individual homogeneous sites, in the order of in area), through meso-ecosystems (landscape mosaics, in the order of ) to macro-ecosystems (ecoregions, in the order of ).