Definition: A desert biome is a terrestrial biome which loses more liquid water by evapotranspiration than is supplied by precipitation and includes communities adapted to these conditions.
Comment: Preliminary definition. The semantics and definitions of "mediterranean", "subtropical", "tropical", "temperate", "polar", and similar climate types may be transferred to an "environmental condition" class once the semantics of this class have been established.
Definition: Gravel is an environmental material which is composed of pieces of rock that are at least two millimeters (2mm) in its largest dimension and no more than 75 millimeters.