Restoring a Dynamic Ecosystem to Sustain Biodiversity

Abstract

Over three decades, Tijuana Estuary became highly modified by frequent storms and runoff events that acted synergistically with intensifying land use to deliver tons of sediment to the salt marsh and its tidal channels. The marsh plain became higher, drier, and more hypersaline, with fewer microtopographic features. The result was reduced biodiversity. Because an endangered sparrow continued to use the marsh plain, it was not permissible to remove sediment or recontour the site. Thus, restoration took on new meaning, and efforts shifted to excavation of disturbed uplands and the creation of novel conditions. When subsequent excavations also accumulated sediment, planning expanded to larger areas to be restored in modules over decades. Sedimentation will likely recur during future stormy periods due to the Pacific Decadal Oscillation and global climate change. Thus, biodiversity will best be sustained within an adaptive restoration framework involving large field experiments that show how to sustain all of the native species somewhere in the estuary, even if no single module can provide all essential habitats.