Given the rich biological diversity in California and dramatic loss and modification of its habitats, populations, species, and ecosystems, a concerted effort has emerged to restore large areas of the state's public and private lands. Under these circumstances, ecological restoration represents an important element in the strategy to conserve numerous at-risk species and maintain vital ecosystem services. After reviewing the various motivations for ecological restoration, we identify some of the key challenges, both practical and theoretical, that are likely to affect the success of restoration efforts. We describe a shift in defining restoration success from a focus on recreating historic “pristine” ecosystems to viewing restoration in a dynamic landscape context in which realistic novel ecosystems are accommodated. These accommodations are necessitated by a broad array of challenges that include several global change factors. Finally, we argue that prospects for successful ecological restoration will be enhanced by emphasizing landscape-scale resilience and incorporating restoration into a regionally-coordinated, active adaptive management program.

Native perennial bunchgrasses have undergone steep declines across much of California but persist in sizable populations along the northern coast. The longer rainy season and less severe summer drought in this region are thought to facilitate bunchgrass persistence in the face of extensive invasion by exotic annual species. Changes in the seasonality and intensity of precipitation that accompany global climate change could critically influence efforts to conserve and restore these plants in California grasslands. We established a large-scale manipulation of rainfall in a protected Mendocino County grassland to investigate how predicted shifts in precipitation affect the performance of three native perennial bunchgrass species in exotic-dominated stands. We added seeds, plugs, and mature tussocks of Danthonia californica, Elymus glaucus, and Elymus multisetus into replicate plots of exotic annual grassland and subjected the plots to one of three experimental precipitation regimes: increased winter rainfall, increased spring rainfall, and ambient rainfall. Responses to rainfall addition varied widely by age class and species and depended heavily on seasonal timing of the increase. Establishment from seed was rare for all three species and showed little response to water addition, likely due to concomitant changes in the surrounding communities. Production of exotic annual grasses rose markedly following repeated extensions of the rainy season, and while established bunchgrasses benefited despite this change, new plants could not establish into thickening stands of exotic vegetation. In contrast, survival was high for transplanted plugs and tussocks of all three species across all three rainfall treatments, suggesting that plugs and tussocks can survive a wide range of climatic conditions and high local densities of exotic annual grasses. Restoration approaches focused on these life stages may be most robust to changing climate. Transplanted individuals can provide a continual source of propagules to surrounding areas that then recruit during years in which conditions in the physical and biological environment are amenable to seedling establishment.

There is currently a large regional effort to restore tidal marsh ecosystems in the San Francisco Bay-Delta Estuary involving the commitment of hundreds of millions of dollars and broad landscape-scale habitat manipulations. Although climate change has been on the horizon for many years, recent developments suggest that it must be taken seriously as a factor to be considered in future planning for marsh restoration efforts. Tidal marshes are vulnerable to changes in salinity and inundation rates, both of which will be affected by climate change. Restoration sites may be particularly vulnerable given unpredictable sediment inputs and newly established vegetation. Predicted shifts in snowmelt and altered runoff will change estuarine salinity patterns and could have large-scale impacts on marsh dominance, especially for freshwater marshes. Even relatively small salinity changes could lead to shifts in dominant species, with freshwater marshes being replaced by brackish marshes and brackish marshes converted to salt marsh communities. This will cause a reduction in overall estuarine plant diversity and productivity, with possible reverberations for the estuarine food web. Based on monitoring data from San Francisco Bay marshes, we predict that salinity will have a more immediate impact on tidal marsh vegetation than sea-level rise. However, sea-level rise poses a potentially greater long-term threat, depending on its rate, because the effects of inundation and a more persistent salinity regime could cause widespread marsh loss. If ice sheets in Antarctica and Greenland begin melting at rapid rates, inundation impacts could be catastrophic for coastal marshes. Given the magnitude of these potential changes, we urge the restoration and conservation management community to integrate these contingencies into adaptive management process and to join with the broader community in forging more flexible governance institutions that can respond effectively to large-scale uncertainties and trajectories as they unfold.

We investigated changes in vegetation composition of different grass buffer strips in a fragmented coastal agricultural landscape to evaluate the potential for native grass restoration of sites that receive agricultural runoff. Vegetative buffers bordering Elkhorn Slough, draining into Monterey Bay, California, were either seeded with a non-native annual grass (Hordeum vulgare) or with a mix of native perennial grasses (Bromus carinatus, Deschampsia cespitosa, Nassella pulchra), and above-ground biomass and cover of vegetation were measured over a 4-yr period. Based on preliminary results, we initiated a second, smaller-scale experiment to test establishment of native perennial grasses (Bromus carinatus, Elymus glaucus, Hordeum brachyantherum) at different seeding densities with combinations of non-native annual grasses (H. vulgare or Lolium multiflorum and Vulpia myuros) to optimize erosion control.

In the first experiment, plots seeded with non-native annual grasses had greater biomass than native perennial plots in the first year. Biomass and cover of seeded annual grass decreased each year, which resulted in these plots being dominated by unseeded non-native species by the third year. In contrast, seeded native perennial grasses increased in both biomass and cover by the second year, with little cover of non-native species; but, in the third year cover of non-native species increased. By the fourth year, unseeded non-native species provided nearly all plant biomass and cover in all treatments. In the second experiment, native perennial grass cover was low, but was greater when seeded alone compared to when seeded with non-native annuals. The seeded annual grass V. myuros invaded and provided the majority of cover in most plots by the second year. Our results suggest that some species of native perennial grass can establish on former agricultural lands, but long-term survival is difficult without extensive management.

Despite the biological, social, and physical challenges that exist in urban creek restorations, there are opportunities to effectively involve local residents in ecological rehabilitation projects. An urban riparian restoration project along Strawberry Creek (Berkeley, CA) began with the goal of removing exotic vegetation and restoring native plant coverage. However, through the involvement of local high school and college students, the project accomplished an additional goal of educating the local community about restoration and conservation. Undergraduate students at the University of California, Berkeley conducted pre-restoration vegetation surveys of species richness and cover in order to assess initial species composition at the restoration site. Berkeley High School students, under the guidance of UC Berkeley graduate student mentors, removed exotic vegetation from an 800 m² area of the riparian zone and replaced exotics with over 500 individual native plants. Post-restoration vegetation surveys found that this project succeeded in reducing the cover of exotic vegetation and increasing native species richness. A smaller area adjacent to the student plantings was more intensively maintained by the University of California, Berkeley Office of Environment, Health & Safety and had a higher survival rate among the natives planted. Student attitudinal surveys indicated that students' involvement in the restoration activities increased their awareness and appreciation of the creek's value and educated them about scientific concepts of restoration and conservation. In spite of the various challenges of coordinating several interest groups, the involvement of local students has the potential to increase the likelihood that the project will succeed in the long term, especially if such involvement signals greater appreciation for the creek habitat.