The spatial structure of a plant community or an ecosystem is understood as a part of the total structure of the community (or ecosystem). The distinction between the space heterogeneity of the environment and that of the biotic component of the ecosystem is emphasized. The heterogeneity can be evaluated on different levels (using different scales). A whole system of space-structure units can be formed, encompassing the landscape complex of ecosystems or of communities, the local complex of ecosystems or of communities, the ecosystem or community, the microcoenosis and the structural group of species. There are several definitions of ecotones but their applicability is often limited.