Another major factor that controls the distribution of vegetation within the Everglades is the hydrologic pattern, which is defined by the depth, timing, and duration of inundation (flooding) as well as the quality and salinity of the source water. The flat topography, temporal distribution of rainfall, and proximity to the coast all interact to determine the hydrologic regime. Surficial geology and overlying soil type also influence the composition and abundance of plant species. Disturbances, both natural (including fire, freezes, hurricanes, etc.) and human-caused (such as altered fire regimes, drainage, development, and introduction of exotic pest plants), also impact vegetation patterns.