Losses have been significant. California native grasslands have been reduced to about one percent of their original extent, both through land conversion and degradation by exotic species invasions. Other seriously threatened ecosystems include wetlands and riparian woodlands, which have been reduced to 10 percent or less of their original area. Many of the animal species dependent on these habitats have declined as well.
Like California, the Elkhorn Slough watershed is rich with diverse habitats and animals. However, the watershed also faces many of the threats. For example, many of the Elkhorn Slough Reserve’s grassland and oak woodland understories are highly invaded by exotic plants; its freshwater springs have been almost entirely lost due to groundwater overdraft; and 75% of its historical salt marshes have been lost through conversion.
In order to preserve the important natural habitats that remain, the Elkhorn Slough Reserve’s stewardship program gives high priority to habitat protection within Reserve boundaries. In areas already degraded by past land uses, invasive species, or pollution, the stewardship program endeavors to sustainably restore at least some of the lost aspects of local biodiversity and natural processes.
Priority Topics
Protection of Intact, Native Habitats and Sensitive Species
The conservation of relatively pristine estuarine, freshwater, maritime chaparral, coastal prairie, coastal scrub, and coast live oak habitats is a high priority for the Elkhorn Slough Reserve stewardship program, as is the protection of sensitive species. In general, the protection of native species and assemblages relies on the removal of stresses that degrade or impair conservation targets. Several of these stresses can be addressed through strategies of prevention, early detection, and rapid response. For example, working together with the Elkhorn Slough Reserve education program, we are attempting to protect local coast live oak woodlands by preventing the introduction of the Sudden Oak Death pathogen, which has led to significant declines in other California coast live oak woodlands. We also work with Reserve researchers to adaptively manage freshwater habitats used by threatened and endangered amphibians. The stewardship program also works on early detection and eradication of newly introduced invasive species, and erosion control to protect sensitive species, oak woodlands, native grasslands, and wetlands from polluted runoff originating offsite.
Restoration of Degraded Conservation Targets
The Elkhorn Slough Reserve is the site of many degraded habitats. As a result, a large portion of the Reserve’s habitats are in need of restoration in order to recover at least some of the lost aspects of local biodiversity and natural processes. As much as possible, Reserve restoration projects are designed as restoration science projects, incorporating both existing knowledge and experimentation into the design, allowing us to focus on important questions about how to make a given project achieve its goals. Data from monitoring not only helps guide future projects on the Elkhorn Slough Reserve but information also is shared to help others better restore habitats throughout the region.
As part of restoration, the stewardship program oversees an exotic species control program. This program has been developed primarily to protect native habitats and threatened and endangered animals, but is also an important component of most upland restoration projects. Invasive species control is critical, because animal invaders can cause extinctions of vulnerable native species through predation, competition, and habitat alteration. Plant invaders can completely alter the fire regime, nutrient cycling, hydrology, and energy budgets in a native ecosystem, and greatly diminish the abundance or survival of native species. Furthermore, some non-native animals and plants can hybridize with native species. Therefore, controlling the abundance of and outlying populations of exotic species are important actions to take to protect and restore native species.
In support of restoration projects, the stewardship program also includes the maintenance and management of an on-site native plant greenhouse.
Habitat Management
Constraints sometimes preclude the true restoration of lost natural processes, habitats, and species. For example, Reserve stewards cannot restore natural freshwater seeps and springs with existing resources. Freshwater has been overdrawn, and saltwater intrusion is a problem. Instead, the Reserve has been supporting man-made guzzlers and ponds for wildlife. These waterbodies now support breeding populations of threatened and endangered amphibians. In these and other cases, Reserve stewards currently maintain man-made structures or management regimes instrumental in the upkeep of habitat. For example, Reserve stewardship staff maintains plumbing to guzzlers and selected ponds; maintains and manages tide gates at the Reserve’s North Marsh; and mows or oversees cattle grazing in selected grasslands in an attempt to decrease the impact of weeds and simulate grazing by now locally-extinct herbivores, such as the Tule Elk.
Historical Ecology
Historical ecology is the recovery and synthesis of diverse, underutilized, and diminishing historical data sources, in order to make sense of past and present ecosystems. It is an emerging field which, in Northern California, has been pioneered by the San Francisco Estuary Institute’s Historical Ecology program. Historical ecology can help us understand past and current conditions, including how natural ecological and physical processes have functioned over long periods of time, and how present-day conditions have developed. Furthermore, historical ecology can help guide science-based restoration and management decisions, by helping us understand the restoration potential of various sites, and using history as a restoration reference. Working collaboratively with the research program, the Elkhorn Slough stewardship program researches and acquires copies of original maps, journals, surveys, botanical collections, archaeological data, and geologic cores from a variety of sources, and synthesizes the information in documents and public presentations, in order to reveal the past and help inform the future.
