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Gardena Willows Wetland Preserve
The Gardena Willows Wetland Preserve occupies of land owned by the City of Gardena, in Los Angeles County, California. The preserve has of wetland and of upland.〔Jones & Stokes Associates, Inc. (1999). A Plan for the Gardena Willows Wetland. March (JSA 99-013). Sacramento, CA.〕 The wetland acres have a natural depression where water remains for such a significant time that plants and animals not adapted to water and saturated soils cannot survive. The upland, which remains dry outside of the rainy season, supports plants which thrive with these drier conditions. The preserve is the last intact remnant of the former Dominguez Slough, an important vernal marsh that once covered as much as of this area, known as the South Bay region of Los Angeles County. The Slough is a part of the Dominguez Watershed, 96% of which is now covered with concrete and man-made structures. It is believed that prior to the arrival of concrete, the Tongva, the native people of this region, were able to commute by canoe, not car, around much of the South Bay.〔Baldwin, Randy (2010) Gardena Willows Wetland Preserve, documentary. Randy Baldwin of RB Media Werks.〕 Tongva villages were located throughout much of what is now Los Angeles and Orange Counties as well as islands just off the coast.〔http://www.tongvatribe.net/〕
In 1918 a drainage canal off the Los Angeles River was the first construction project which ultimately led to the end of the Dominguez Slough. After the completion of this canal, during the next fifty years the Slough was filled for various construction projects of the growing megalopolis of Los Angeles County.〔 The Dominguez Channel was built in the 1920s to replace natural drainage provided by the Slough; today the Channel drains about 62% of the area of the former Dominguez Watershed, focusing water into the Los Angeles Harbor.〔〔Map of Dominguez Channel: http://dpw.lacounty.gov/wmd/watershed/dc/DCMP/docs/Dominguez%20Front.pdf〕 In the 1970s, two young Gardena residents became concerned about the mass destruction of willow trees they had witnessed during their short life-times. They sought a way to protect the remaining willows and ultimately contacted the United States Army Corps of Engineers. The Corps recognized the area as a waterway under their jurisdiction and provided federal protection against further destruction of the wetland and the upland immediately surrounding it.〔 Today, eight of the preserve’s wetland acres remain under jurisdiction of the Corps while all 9.4 of the wetland acres are under California Department of Fish and Game jurisdiction. The hydrology, soils and native vegetation of the preserve determine these jurisdictional markers.〔 The preserve was federally protected from exploitation by environmental laws of the 1960s and 1970s specific to the protection of wetlands.〔 These environmental laws, such as the Clean Water Act, enacted in 1948 and substantially revised in 1972,〔http://www2.epa.gov/laws-regulations/summary-clean-water-act〕 reflected growing awareness of the unique ecology and environmental significance of wetlands.
== Ecology ==
The preserve, a remnant wetland of a once-great watershed, is now surrounded by urbanity: 2 major freeways, 2 major boulevards and a large strip mall define its southern and eastern boundaries. A large residential area, 2 Senior housing complexes and a city park hug its northern and western boundaries. Today the Dominguez Watershed is a complex system of storm drains and flood control channels.〔(【引用サイトリンク】 title=Water Damage Restoration division Los Angeles )〕 The preserve’s wetlands are now fed by these storm drains, as well as by urban runoff and rain. It is possible that urban runoff, from activities such as excessive landscape irrigation and car washing, now brings water into the preserve in greater quantities and with greater regularity than occurred naturally. These factors may be favoring the growth of the "willow dominated riparian forest" (p I-8)〔 and moving the preserve away from being a vernal marsh. Conversely, with this high density of urban markers, storm drains and urban runoff entering the preserve bring in nutrient-rich water, perfect for aquatic invasive species, such as water primrose (''Ludwigia''), a management challenge. If allowed to continue to invade the preserve, water primrose will soak up the water in the wetland and ultimately destroy the willows. Storm drains, boulevards and parking lots also bring in trash, which volunteers regularly clear out. In return, the native plants and soil of the preserve clean the storm drained water before sending it on to the Dominguez Channel which feeds to the Los Angeles Harbor and the Pacific Ocean.〔
The preserve's host three vegetative communities: willow riparian forest, freshwater emergent marsh and transition zone. Three species of willows are native to the preserve: Goodding's black willow (''Salix gooddingii''), which provides important canopy habitat, as well as arroyo willow (''Salix lasiolepis'') and narrow leaf willow (''Salix exigua''). On the , coastal prairie and scrublands are the native communities. With this much needed native vegetation, the preserve provides valuable habitat for various insects, amphibians—such as Pacific tree frogs, and reptiles—such as alligator lizards.〔 It also provides a beacon for birds. At the 2010 Christmas Bird Count, a total of 315 birds representing 32 species were identified, including mallards, a peregrine falcon, a red-shouldered hawk and a downy woodpecker.〔 While bird counts remain strong, any birds nesting at or near ground level at the preserve risk losing young to raccoons, nonnative squirrels and semi-feral cats. These predatory ground mammals may also reduce populations of amphibians and reptiles.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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