The Grasslands

Ecology & Conservation

Overview:

The San Joaquin Basin is 80 miles long and covers 2,900 square miles.  It extends from the Stanislaus River in the north, to the San Joaquin River in the south. The basin is bordered on the west by the California Aqueduct and on the east by the foothills of the Sierra Nevada.  Major tributaries to the San Joaquin River include the Chowchilla, Merced, and Tuolumne Rivers.  Most private wetlands as well as several federal and state managed areas in the San Joaquin Basin are located in the Grassland Resource Conservation District (GRCD) on the western side of the basin. 

Habitat Description:

Wetlands in the Grasslands include freshwater marshes, riparian woodlands, and vernal pools.  The rivers and sloughs support vast freshwater marshlands dominated by aquatic and emergent vegetation―rushes, bulrushes (tules), sedges, and cattails―and fringed with willows, cottonwoods, and a variety of shrubs.  Riparian wetlands include rivers, creeks, and streams and their plant communities, most notably woody vegetation.  Vernal pools form where natural depressions occur in non-porous soils and are seasonally flooded by winter rains.  When the rains stop, the water eventually evaporates. These ephemeral wetlands remain flooded long enough to prevent typical grassland vegetation from taking hold, resulting in a unique assemblage of plants and animals, some of which are found nowhere else.  

Upland areas adjacent wetlands also provide forage, loafing areas, thermal cover, and nesting habitat for a variety of migratory bird species.  Upland habitats include not only native grassland and alkali scrub, but grain and hay crops, and grazed or ungrazed pasture.  Some harvested cornfields are intentionally flooded to provide waterfowl and waterbird habitat.

Shorebird Highlights:

Common shorebird sightings in the Grasslands include: black-necked stilts and killdeer year-round; greater yellowlegs, long-billed curlews, least sandpipers, dunlin, and long-billed dowitchers from autumn through spring; American avocets and Black-bellied plover during the cool, wet winter and spring; and lesser yellowlegs and Wilson’s snipe in the fall and winter.  Western sandpipers are common, while whimbrels and short-billed dowitchers are occasionally seen during fall and spring migrations.  Rare sightings include solitary sandpipers, willets, spotted sandpipers, marbled godwits, pectoral sandpipers, Wilson’s and red-necked phalaropes. 

Other Important Wildlife:

The Grasslands is the winter home for large portions of the Pacific Flyway populations of many species of waterfowl, waterbirds, raptors, and songbirds.  The majority of Aleutian cackling geese winter here as well as thousands of greater white-fronted geese, snow geese, and Ross’s geese.  Quantities of northern pintails, wood ducks, and sandhill cranes are among the more notable sights. 

It is also the year-round home of a number of endangered, threatened, and candidate species, unique endemics, and other species of special concern, including the riparian brush rabbit, San Joaquin Valley kit fox, tule elk, Fresno kangaroo rat, San Joaquin pocket mouse, giant garter snake, San Joaquin whipsnake, Pacific pond turtle, tri-colored blackbird, yellow-billed magpie, Nuttall’s woodpecker, western yellow-billed cuckoo, yellow-breasted chat, Valley elderberry longhorn beetle and a number of unique vernal pool species of fairy shrimp and tadpole shrimp. 

Impacts and Disturbance:  

Agricultural and urban development have destroyed or modified more than 95% of the historic wetlands and over 90% of all riparian habitats in the Central Valley, Two thirds of those remaining wetlands are in private ownership.

Virtually all Central Valley habitats have been altered.  Over 526 species of introduced plant species are known from California, and many of these occur in the Central Valley’s Grasslands.  In most habitats native taxa comprise less than 1 percent of the standing grassland crop. Introduced annual grasses now dominate grassland habitats.  Agricultural development, urban expansion, alteration of hydrologic regimes and channelization, grazing by domestic livestock, fires, and introduced plants and animals have all contributed to the pervasive destruction of native habitats. 

Intensive agricultural development has left few freshwater marshlands, and those that are left are generally degraded and heavily managed for duck production, water impoundments, or runoff and effluent storage. Dams, channelization of rivers, and pollution continue to threaten the unusual and productive freshwater biodiversity of the region.

Out of 416 km2 of remaining riparian woodland, only about 40 km2 or 1% percent of original riparian woodlands can be considered intact. Channelization, dams, clearing for pasture, flood control, alien plants, overgrazing by domestic livestock, fires, and logging have all taken their toll. 

An estimated 11,310 km2 (2.8 million acres or 66%) of vernal pools have been destroyed, with the most intact pools left on the higher terraces. Agriculture, conversion to pastureland, water diversion and channelization, and draining have all taken their toll on these unique habitats. The USFWS has just begun an ecosystem recovery plan for over 40 species dependent upon vernal pools. 

Remaining patches of relatively undisturbed native habitats are severely fragmented and isolated.  Loss of habitat linkages are likely to be most significant for species that rely on contiguous riparian woodlands for dispersal corridors, such as migratory warblers, cuckoos, reptiles, and amphibians.

Shorebirds in the Grasslands currently rely on a variety of habitats to meet their food energy needs, including evaporation and sewage ponds which may expose them to concentrated contaminants like selenium, or increase the probability of disease transmission.

Threats to Habitat:

The Grasslands is threatened with loss of habitat quantity and quality by urban encroachment, conversion to intensive agriculture and industry, water availability, pollution, alteration of hydrologic regimes, channelization, fires, invasive species, high operation and maintenance costs, and threats to eliminate waterfowl hunting which supports wetland habitat.  Populations of the tri-colored blackbird are declining precipitously due to loss of breeding habitat and changes in agricultural practices. Many amphibian species show dramatic declines associated with habitat loss. Extensive riparian forests and woodlands have been destroyed by decades of tree-cutting, channelization, and flood-control projects. Salinization, toxic runoff, and erosion from ecologically-unsound agricultural practices increasingly degrade habitats. 

Water availability is the #1 concern; without water there is no wetland.  The Central Valley Project Improvement Act approved by the U.S. Congress in 1992 provides some of the Grasslands with a reliable water supply. However, the long-term status of this legislation is threatened by other interests.  Additional threats to the Grasslands water supply and management includes competition with municipal water providers and proposed restrictions to wetland restoration and water uses.  Securing firm, reliable water supplies for managed wetlands in the Central Valley will become even more challenging in the future.  Demand for limited water supplies continues to increase with continued population growth in California, and wetlands compete for a legitimate allocation to meet wetland-dependent resource needs. Some of the most significant barriers to acquiring future water supplies for Central Valley wetlands include: Delta export and pumping constraints; increasing competition to purchase limited water supplies; timing of water use on shared conveyance systems; increasing regulation of managed wetland water discharge; capacity limitations of existing water delivery systems; lack of balance between supply and demand; cost of acquiring annual and long-term water supplies; current and future, state, federal, and private budget shortfalls that impact acquisition efforts;  the State of California’s ability to meet their 25% cost-share obligations under the CVPIA; unreliable quality and quantity of groundwater supplies; increasing groundwater pumping costs; and annual and long-term water transfers that may adversely affect managed wetlands and fish and wildlife resources.  Groundwater issues including access, poor water quality, overdraft, and subsidence.  Soils on the western side of the San Joaquin Basin are derived from marine sediments that are high in salts and trace elements. Post-harvest irrigation was formerly used to leach these substances from the upper soil, and return flows were used as a wetland water source. Selenium concentrations in this tailwater proved damaging to a wide range of birds and consequently, use of this water has been greatly restricted.  Stricter RWQCB standards for wetland discharges into the San Joaquin River are pending (e.g., boron, methylmercury, salinity, dissolved oxygen and selenium).

Habitat Protection Measures:

Protection is provided to 76% (132,241 acres) of the Grasslands by virtue of federal and state ownership and by private lands with perpetual conservation easements. Of the existing wetlands in the Central Valley, about two thirds are privately owned.  Ensuring that water supplies are attached to the property when protecting managed wetland habitat is a priority.  Federal, state, and private landowner organizations―including the California Waterfowl Association, Ducks Unlimited, Grassland Water District, Grassland Resource Conservation District, California Department of Fish and Game, USDA Natural Resources Conservation Service, and the U.S. Fish and Wildlife Service―have identified critical areas that need protection to preserve the wildlife habitat values of the Grasslands. These organizations have developed biological justification documents for establishment of an agricultural buffer zone between the Grasslands and expanding urban areas. 

The Central Valley Joint Venture (CVJV) is one of 17 Joint Venture partnerships in the United States, established under the North American Waterfowl Management Plan, and funded under the annual Interior Appropriations act. The CVJV brings together conservation organizations, public agencies, private landowners and other partners interested in the conservation of bird habitat within California’s Central Valley.  The mission of the Central Valley Joint Venture is to work collaboratively through diverse partnerships to protect, restore, and enhance wetlands and associated habitats for waterfowl, shorebirds, waterbirds, and riparian songbirds, in accordance with conservation actions identified in the Joint Venture’s Implementation Plan.  The 2006 Central Valley Joint Venture Implementation Plan (2006 Plan) allows the Central Valley Joint Venture and its individual partners to examine the habitat needs of various bird groups in the nine basins within the Central Valley, and to formulate and prioritize activities to meet those needs.

Strict protection and restoration of the last remnants of native communities is needed for all valley habitats. 

Management Activities and Priorities:

The Grasslands is intensively managed for wildlife.  The area has a very sophisticated system for water delivery and management. Nearly 90% of all wetlands are managed on a seasonal basis.  Managed wetlands are broadly categorized as seasonal, semi-permanent or permanent. Seasonal wetlands are typically flooded in the fall, with drawdown usually occurring between March and May. Semi-permanent wetlands are usually flooded from early fall through early July, while permanent wetlands are flooded year-round.  

Th e Joint Venture’s assessment of habitat conditions in the Central Valley suggests that shorebird needs may be met by: (1) managing wetlands and agricultural habitats to provide foraging depths <10 cm; and (2) adjusting flooding and draw down schedules of wetlands to meet the needs of wintering shorebirds, especially during July and August.

Population objectives are highest in April, with shorebird numbers reaching a minimum in July. Seasonal wetlands provide the majority of foraging habitat.  Conservation objectives for managed seasonal and semi-permanent wetlands for the San Joaquin Basin are that nearly 66% of the seasonal wetlands present in this planning region (40,130/61,013 acres) must provide foraging depths <10 cm during some portion of the wintering period if seasonal wetland objectives for shorebirds are to be met.

Management of the Grasslands has improved significantly since the inclusion of the Grasslands as an international shorebird reserve. The implementation of the Central Valley Project Improvement Act in 1993, the purchase and restoration of about 2,000 acres of wetlands by the U.S. Fish and Wildlife Service and California Department of Fish and Game, the implementation of the California Waterfowl Habitat Program on 7,447 acres of private lands, continual acquisition of perpetual conservation easements from willing sellers via the USDA Natural Resources Conservation Service and the U.S. Fish and Wildlife Service, annual marsh management workshops sponsored by the Grassland Resource Conservation District for private landowners, and technical assistance provided to private wetland owners by the U.S. Fish and Wildlife Service, California Department of Fish and Game, and the Grassland Water District are some of the programs that continue to improve wetland management in the Grasslands.

Research:

The Grasslands hosts a myriad of graduate, doctoral, federal, state, and non-governmental organization research projects on a wide variety of subjects, including wildlife, botany, ecology, contaminants, and management.  

Documents and References:

Central Valley Joint Venture 2006 Implementation Plan