CRB:Manipulation of Vertical and Horizontal Heterogeneity in a Large-Scale, Restoration Experiment

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0212005ZedlerEcosystem degradation often involves the loss of topographic heterogeneity, a criticalecosystem property that declines as sediments fill in depressions, flatten surfaces andraise elevations. In southern California, coastal habitat that is highly valued for itssupport of endangered plants and animals has suffered catastrophic sedimentation,followed by altered species distributions and lowered biodiversity. When recovery isattempted, topographic complexity is typically ignored as sediments are excavated andrestoration sites contoured by bulldozer. Insufficient vertical and horizontalheterogeneity might be a key constraint on the restoration of wetlands toward structuraland functional equivalency with undisturbed sites.In this project, we will investigate how adding topographic heterogeneity mightaccelerate the progress of ecosystem restoration. The principal hypothesis is that addingvertical and horizontal pattern at to will facilitate the restoration of wetland structure andfunction. To test this hypothesis, an entire 8-ha tidal wetland restoration site within theTijuana River National Estuarine Research Reserve (San Diego County, CA) wasdesigned to support the large-scale, ecological experiment. The $3.1-million excavationwas 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 wasreinstated. We propose to take full advantage of the experimental treatments andexamine the influence of (1) a vertical pattern of topographic heterogeneity, in the formof complex tidal creek networks, and (2) a horizontal pattern furnished by varyingdensities of planted salt marsh halophytes, on the diversity, abundance and compositionof multiple response variables and trophic levels: geomorphology, algae, vascular plants,invertebrates, and fish.In addition to testing methods for recovering wetlands, the integrative work proposedherein will demonstrate the power of restoration experiments and contribute fundamentalnew insights into the relationship between topographic heterogeneity and thedevelopment of ecosystem structure (species composition and abundance) and function(e.g., foraging by fish). Conservation and Restoration Biology (CRB).