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<br />002\:177 <br /> <br />The Alamar River: A River Corridor <br />with Outstanding N atmral Resources <br /> <br />With contributions by SDSU students Jennifer Davies and Rey Soto; ASU students <br />Melissa Barry and Allison Yerger; and UABC student Jorge Aramburo. <br /> <br />Introduction <br /> <br />When looking at the urbanized landscape today, it is easy to forget that at one time <br />riparian vegetation traced the entire length of numerous rivers in the Tijuana-San Diego <br />metropolitan region (Shapiro 1991: 20). For example, riparian habitats once flourished in <br />the Tijuana, San Diego, and Sweetwater river valleys. Today, most riparian vegetation <br />corridors have become concrete flood control channels. In Southern and Baja California, <br />few isolated regions of riparian vegetation exist and most of these are disturbed. <br /> <br />Even though the Alamar River riparian habitat is not pristine, its long, green riparian <br />corridor is "natural" compared to the intensely developed land that surrounds the river <br />and the concrete channelized Tijuana River (Zona Rio) downstream (see photograph 2, <br />page 21). The Alamar River forms the most extensive riparian corridor in the Tijuana <br />metropolitan region. It is a virtually unbroken line of riparian woodland and scrub from <br />Mesa de Otay to Tecate. Since so few riparian wetlands exist in California or Baja <br />California, the Alamar River's environment is vital to migratory bird species including <br />the endangered Least Bell's vireo. The benefits of the Alamar River's riparian areas for <br />people, plants, and animals include the provision of basic necessities such as clean water, <br />clean air, shelter for animals from temperature extremes, and food. In addition, wetlands <br />in riparian corridors are instrumental in flood control, groundwater recharge, and <br />improving water quality (Shapiro 1991). <br /> <br />A Biogeography of Riparian Habitat <br /> <br />Riparian habitats consist of riparian plant assQ(;iations (vegetation) that occur adjacent <br />to a channel of water and/or in river floodplains (Lowe 1964). Given the optimal <br />conditions of light, water, and nutrients, riparian corridors are extremely productive in <br />terms of plant biomass and biodiversity, or the number and variety of animal and plant <br />species present. Supervised by Jose Delgadillo, Director of the Herbarium at UABC, <br />Ensenada, the BorderLink 2000 research team conducted a riparian vegetation survey of <br />the Alamar River Corridor (see photograph 3, page 21). A summary ofthe plant survey is <br />provided in the Appendix. According to Delgadillo, the survey revealed three strata, or <br />layers, of riparian vegetation present in the Alamar River Corridor, and aquatic and semi <br />aquatic plants within the flow of the river. These layers are: <br /> <br />Arboreal or woodland vegetation. In Zones 1 and 2, willow woodlands are present, <br />dominated by native willow species (Salix gooddingii and Salix lasiolepis). Upstream, in <br />less disturbed and less polluted areas, mixed woodlands exist. These are characterized by <br />willows, native Fremont Cottonwood (Populus fremontii), and some California Sycamore <br /> <br />29 <br />