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Declining Biodiversity: Why Species Matter and How Their Functions Might Be Restored in Californian Tidal Marshes

2001; Oxford University Press; Volume: 51; Issue: 12 Linguagem: Inglês

10.1641/0006-3568(2001)051[1005

1525-3244

Joy B. Zedler, John C. Callaway, Gary Sullivan,

Botany, Ecology, and Taxonomy Studies

S diversity is being lost in habitats that are increasingly diminished by development, fragmentation, and urban runoff; the sensitive species drop out and a few aggressive ones persist, at the expense of others. Alarmed by declining biodiversity, many conservationists and researchers are asking what happens to ecosystem functioning if we lose species, how diverse communities can be restored, which (if any) particular species are critical for performing ecosystem services, and which functions are most critical to ecosystem sustainability. In southern California, 90% of the coastal wetland area has been destroyed, and remaining wetlands continue to be damaged; even the region’s protected reserves are threatened by highway and utility-expansion projects. The fate of biodiversity in these diminished wetlands serves to warn other regions of the need for continual assessment of the status and function of both common and rare species, as well as the need for experimental tests of their importance—before they are lost. This article synthesizes data for tidal marshes of the Californian biogeographic region, which stretches from Point Conception near Santa Barbara south to Bahia San Quintin in Baja California. We focus on the broad marsh plain, which is dominated by eight species of halophytes (salt-tolerant plants; Figure 1). From regional censuses, we document the recent loss of short-lived species from several wetlands. From eyewitness accounts of tidal-exclusion events at Estero de Punta Banda and Tijuana Estuary, we link species loss to the interruption of tidal influence. And from experimental plantings of marsh halophytes in a bare restoration site, we document the difficulty of restoring plant diversity, demonstrate Joy B. Zedler, Aldo Leopold Chair of Restoration Ecology, Botany Department and Arboretum, 430 Lincoln Drive, University of Wisconsin– Madison, Madison, WI 53706, is a wetland ecologist who has studied southern California coastal wetlands for about 30 years. John C. Callaway, assistant professor in the Department of Environmental Science, University of San Francisco, San Francisco, CA 94117, conducts field research at Tijuana Estuary and San Francisco Bay; he is a wetland ecologist whose research focuses on sediment and vegetation dynamics in restored wetlands. Gary Sullivan is a wetland ecologist with experience in freshwater lakes and streams, estuaries, and salt marshes; his current focus is on restoring large wetlands along the Illinois River for a nonprofit organization, The Wetlands Initiative, Chicago, IL 60604-3703. © 2001 American Institute of Biological Sciences. Declining Biodiversity: Why Species Matter and How Their Functions Might Be Restored in Californian Tidal Marshes