Ecosystem degradation often involves the loss of topographic heterogeneity, a critical ecosystem property that declines as sediments fill in depressions, flatten surfaces and raise elevations. In southern California, coastal habitat that is highly valued for its support of endangered plants and animals has suffered catastrophic sedimentation, followed by altered species distributions and lowered biodiversity. When recovery is attempted, topographic complexity is typically ignored as sediments are excavated and restoration sites contoured by bulldozer. Insufficient vertical and horizontal heterogeneity might be a key constraint on the restoration of wetlands toward structural and functional equivalency with undisturbed sites. In this project, we will investigate how adding topographic heterogeneity might accelerate the progress of ecosystem restoration. The principal hypothesis is that adding vertical and horizontal pattern at to will facilitate the restoration of wetland structure and function. To test this hypothesis, an entire 8-ha tidal wetland restoration site within the Tijuana River National Estuarine Research Reserve (San Diego County, CA) was designed to support the large-scale, ecological experiment. The $3.1-million excavation was completed in February 2000 with the connection of the site to a main tidal channel, and we have monitored several attributes over the 22 months since tidal flushing was reinstated. We propose to take full advantage of the experimental treatments and examine the influence of (1) a vertical pattern of topographic heterogeneity, in the form of complex tidal creek networks, and (2) a horizontal pattern furnished by varying densities of planted salt marsh halophytes, on the diversity, abundance and composition of multiple response variables and trophic levels: geomorphology, algae, vascular plants, invertebrates, and fish. In addition to testing methods for recovering wetlands, the integrative work proposed herein will demonstrate the power of restoration experiments and contribute fundamental new insights into the relationship between topographic heterogeneity and the development of ecosystem structure (species composition and abundance) and function (e.g., foraging by fish).
Conservation and Restoration Biology (CRB).
