Patterned vegetation is a vegetation community that exhibits distinctive and repetitive patterns. Examples of patterned vegetation include fir waves, tiger bush, and string bog. The patterns typically arise from an interplay of phenomena that differentially encourage plant growth or mortality. A coherent pattern arises because there is a strong directional component to these phenomena, such as wind in the case of fir waves, or surface runoff in the case of tiger bush. Patterns can include relatively evenly spaced patches, parallel bands, or some intermediate between those two. These patterns in the vegetation can appear without any underlying pattern in soil types, and are thus said to "self-organize" rather than be determined by the environment.