Again, the well-known action of earthworms may be said to be a biological work; but the resulting aeration of the soil causes edaphic differences; and earthworms are absent from certain soils, such as peat.
Finally, within any district of constant or fairly constant climatic conditions, it is possible to distinguish plant communities which are related chiefly to edaphic or soil conditions; and the vegetation units of these definite edaphic areas are the plant formations of some writers, and, in part, the edaphic formations of Schimper.
When a district like England is divided into edaphic areas, a general classification such as the following may be obtained:
Such groups are interesting in that they are vegetation units whose physiognomy is, in a broad sense, related more to climatic than to edaphic conditions.
Physical FactorsThese are frequently classified as edaphic or soil factors and climatic factors; but there is no sharp line of demarcation between them.