Boland (1981) found that six species of 

 shorebirds were abundant in his beach study 

 site. These included sanderling, willet, 

 marbled godwit, whimbrel, snowy plover, and 

 black-bellied plover. Additional species that 

 were not present on his beach site but are 

 commonly observed feeding in the intertidal 

 beach areas include the least sandpiper, 

 western sandpiper, and dowitcher. 



Belding's Savannah sparrows often forage 

 on the dunes, especially when an abundance of 

 kelp has washed ashore. The decaying kelp 

 harbors large numbers of insects, especially 

 flies. At Tijuana Estuary, several sparrows 

 nest in small patches of pickleweed and 

 saltgrass that are surrounded by dunes and 

 dune vegetation (White 1986). 



The dunes and beach habitats are dynamic, 

 and recent storm damage has altered the native 

 communities. In order to open the estuary to 

 tidal flushing, the sand that had blown and 

 washed into the estuarine channels was 

 dredged and replaced on the dunes in December 

 1984. A revegetation program designed to 

 stabilize the dunes and prevent recurrence of 

 mouth closure has been initiated (Jorgensen, 

 pers. comm.; B. Fink, SDSL), in prog.). This 

 program includes transplantation of native 

 species, e.g., primrose, sand verbena, and 

 dune ragweed, and comparisons of survival in 

 areas with and without dune fencing to reduce 

 trampling. 



3.9 RIPARIAN HABITATS 



Riparian vegetation is the plant 

 community that develops along the margins of 

 freshwater streams and lakes, where soils are 

 damp and sandy. Traveling upstream along the 

 Tijuana River towards the eastern boundary of 

 the NERR, one encounters noticeable changes 

 in the vegetation lining the channel, reflecting 

 a gradient of decreasing soil and water 

 salinity. Near the point where the river 

 enters the estuary, salt-tolerant species such 

 as pickleweed and salt grass are abundant in 

 the riparian understory. Further upstream, 

 mulefat scrub, dominated by dense stands of 

 Baccharis glutinosa and sandbar willow (Salix 

 hindsiana), occupies most of the floodplain. 



Eventually, the low shrubby vegetation is 

 replaced by magnificent stands of mature 

 riparian forest, characterized by a dense and 

 multi-layered canopy extending from the 

 ground to heights of 15-20 meters. Here, 

 cottonwoods (Populus fremontii), several 

 species of willows (Salix spp.), and mulefat 

 are among the most common plants. The 

 stretch of the Tijuana River that runs through 

 the reserve is contiguous with one of the 

 longest unfragmented riparian woodlands in 

 San Diego County. 



Although less than 10% of the NERR has 

 riparian vegetation, the value of this habitat 

 type to wildlife is high relative to its acreage. 

 Riparian habitats support more species of 

 birds than any other habitat type in 

 California; over 140 species occur there, 88 

 of which are obligate riparian species (Faber 

 et al. 1989). For the NERR and the adjacent 

 Tijuana River Valley, a total of 378 species of 

 birds have been recoreded (Jorgensen, pers. 

 comm.). 



Birds use riparian habitat for nesting, 

 wintering, or both. The mammalian commun- 

 ity is also diverse, with species that dwell 

 primarily in riparian woodlands, such as the 

 long-tailed weasel and bobcat, and species 

 from arid uplands that depend on the 

 availability of water, forage and thermal 

 cover for their survival. Insects are abundant 

 and play important ecological roles as both 

 predators and prey. Many species of fish, 

 reptiles and amphibians occupy riparian 

 habitat and contribute to its unparalleled 

 diversity. According to the Council on 

 Environmental Quality (1978, cited in Faber 

 et al. 1989), "no ecosystem is more essential 

 than the riparian system to the survival of the 

 nation's fish and wildlife." 



Part of the reason for the high diversity of 

 the riparian community lies in its structural 

 complexity, which allows for "niche 

 partitioning" among the many organisms 

 seeking food, nest sites, and cover. The 

 presence of tall trees and a dense, luxuriant 

 understory creates a microclimate that differs 

 from that of adjacent upland habitats in its 

 high humidity and cooler temperatures. 

 Insects thrive in this environment, and are an 

 abundant and dependable food source for many 



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