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<br />54 <br /> <br />the semiarid and arid parts of the world. Riparian zones often lack clear <br />deUni tion in other more humid areas. Struc:turally, all riparian <br />ecosystems have, at least three things in connnon: <br /> <br />1) "Topographically, individual ripa.rian ecosystems form linear <br />continua which, as part of a watershed, a.re branched (or <br />dendritic), with small branches joining lalrger ones t,) form <br />trunks or the main stem in a downstream direction. <br /> <br />2) ,They are part of surface or subsurface hyd.rologic systems <br />which supply the riparian ecosystems with water from remote <br />sources in excess of that available by pre,cipitation. The <br />additional water creates a mesl,,: or hydric: condition. <br /> <br />3) They have terrestrial soils con,taining high moisture levels <br />resulting from a high Iotater table, periodic overbank "ater <br />flows, or flooding. However, dparian ecc,systems are not <br />necessarily submerged for at least part of each year liS <br />wetlands and the soils are not necessarily' subjected to <br />waterlogging like wetlands. <br /> <br />s.,........... ---...., <br /> <br /> <br />'lllU'.'.Rip..'t/l"'on..~..ld.n!l".dl'>l.tI..p,.u..e.Qr..,.I" <br />'_I1'l.lr~""....IIo".~lIo1""CH'U"!lOV"....I"', <br /> <br />(Modified frolll IHCM"SlItl "I. 191~) <br /> <br />By definition, ripar1sn ecOsyste1lS are ~'etland ecosystems whie:h have a <br />high water table because of their proximity to an aquatic ecosystenl or <br />subsurface water. They usually occur as transitional zones or ecotones <br />between aquatic and terrestrial (upland) ecosystems, but have distInct <br />vegetation and soil characteristics. Aridit~, topographic relief, and the <br />presence of depositional soils most strongly influence the extent of high <br />water tables and associated riparian ecosystems. Riparian ecosyste:ms are <br />mo~t commonly recognized as bottomland or floodplain forests in the, eastern <br />U.S. and as bottomland, floodplain and,streambank vegetation in the western <br />U. s. Riparliifilcbayliteu are uniquely chsrac:terized by a combination of: <br /> <br />1. higb species diversity <br />2. ,high species 4ensity <br />3. ,high prodUCtivity, 'and <br />