California’s rivers and estuaries have been dramatically transformed over the past ca. 250 years by human activities such as channelization, urbanization, dredging, and dam construction. Many of these systems are currently the focus of significant restoration and ecosystem management efforts. However, fundamental questions about the ecological structure and functions of these systems under more natural conditions remain unresolved, and locally appropriate restoration targets are often far from clear. This uncertainty is compounded by projections of future climate scenarios, which suggest the likelihood of greater frequency and/or severity of floods, droughts, and high temperature extremes. Past ecological changes coupled with anticipated shifts in climatic drivers raise questions about how restoration, conservation, and management targets and strategies should be identified, in particular regarding the relevance of historical information about how landscapes functioned in the recent past.
Over the past 20 years we have conducted detailed, extensive local studies on the historical ecology of numerous California rivers and estuaries to assess the role of history in informing restoration. We have integrated diverse sets of historical cartographic, textual, and photographic data to reconstruct the former ecological and hydrogeomorphic characteristics of systems statewide, develop spatially explicit landscape reconstructions of past conditions, and assess landscape change.
Results/Conclusions
A wide range of riverine and estuarine system types were historically present, including substantial seasonal variability and diversity of forms, physical characteristics, and biological communities. Estuarine habitats ranged from the freshwater tidal wetlands of the Sacramento-San Joaquin Delta to the hypersaline salt flats of intermittently closed lagoons at the mouths of small creeks, while rivers included perennial rivers that supported broad riparian forest and intermittent streams that supported riparian and alluvial scrub. In each place, historical ecology studies reveal forgotten aspects of landscapes, identify features that have been persistent over time, and analyze changes in physical drivers. Further, they illustrate how California landscapes naturally provided diverse ecological functions while still buffering extreme seasonal and inter-annual climatic variability. Many mediterranean-climate systems were were adapted to low/variable rainfall, and could be appropriate models for future environmental management with predicted shifts in local climate. This analysis of historical context and trajectories provides a key perspective on current management issues and insight into how to design resilient, climate-adaptive future landscapes, suggesting that a strong regional understanding of landscape history will be a valuable tool for ecosystem management in a time of global change.