Wood as an ecosystem component - An ecological study of wood as a material has to define two ecosystems of a different level of integration. The small-scale ecosystems are the dwelling houses, where a considerable amount of wood is used for several purposes. Positive effects of wood on the health of the inhabitants are reported. These effects establish the significance of the typical association wood-mankind. The large-scale ecosystem is the global ecosystem of the earth. Ecological diagnostics on this level have to take into account the Second Law of Thermodynamics. Forestry and intelligent use of wood are able to slow down entropy and heat accumulation in the atmosphere.