California Central Valley grasslands
California's Central Valley grasslands represent a unique and historically significant prairie ecosystem that once spanned approximately 13 million acres. Once teeming with diverse wildlife, including large herds of ungulates and numerous bird species, these grasslands have drastically changed since the 19th century due to human activities. Urban development, agriculture, and drainage of wetlands have transformed the landscape, with over 94% of natural wetlands lost, leading to the dominance of non-native plant species. Despite these challenges, pockets of native flora and fauna still exist, particularly in isolated areas like the Carrizo Plain, which serves as a crucial habitat for endangered species such as the San Joaquin kit fox.
The region experiences a Mediterranean climate, characterized by hot, dry summers and cool, rainy winters, which influences its ecological dynamics. Vernal pools, a unique feature of this grassland, create specialized habitats for various plants and animals adapted to seasonal flooding. However, ongoing threats from habitat destruction and climate change, including increased temperatures and altered precipitation patterns, pose significant risks to this ecosystem. Conservation efforts are underway, with various organizations working to protect and restore these vital grasslands, seeking to preserve their ecological integrity for future generations.
California Central Valley grasslands
- Category: Grassland, Tundra, and Human Biomes.
- Geographic Location: North America.
- Summary: Once the most widespread habitat in California, the Central Valley grasslands constitutes a unique prairie. A highly altered habitat, it still harbors diverse native plants and animals.
Few ecosystems in the world would be as unrecognizable to a 19th-century naturalist as California's Central Valley grasslands. Once a North American Serengeti, where perennial grasslands teemed with herds of ungulates and expansive marshes that were covered in millions of ducks and geese, today there are cities, rice paddies, orchards, and cotton fields. Despite this, there are some isolated pockets of what once was so naturally abundant.
Geography and Climate
California's Central Valley spans an area of 60 or more miles (97 kilometers) wide by 400 miles (644 kilometers) long. The area has a Mediterranean climate, with hot, dry summers and cool, rainy winters. It is boxed in on all sides by mountains, with the Pacific Coast ranges to the west, the southern Cascades to the north, the Sierra Nevada to the east, and the Transverse Range to the south.
The valley exists in the rain shadow of the Coast Ranges, resulting in relatively low precipitation, though there is a strong latitudinal gradient in annual rainfall from north to south. The presence of mountains on all sides results in the development of strong inversion layers over the valley, causing both air-quality problems and the development of tule fog, a thick ground-covering phenomenon, in the winter. This famously thick fog is named after the tules, or marsh bulrush plants, that dominated the once-extensive wetlands in the center of the valley. Unfortunately, some 94 percent of these wetlands have been drained and/or converted to agricultural uses, including Tulare Lake, once the largest freshwater lake west of the Mississippi River.
Biota
The grasslands of the Central Valley were originally dominated by perennial bunchgrasses, specifically a few species of needlegrass. Between these bunchgrasses grew fields of annual wildflowers and other spring-flowering forbs, leading naturalist John Muir to describe it as a huge “central garden … all one sheet of plant gold,” humming with birds, the air rich with the bouquet of wildflowers. These grasslands were rooted in sediment as much as 10,000 feet (3,048 meters) deep, the results of thousands of millennia of erosion from the surrounding mountains and volcanic deposition.
This rich, diverse grassland was bordered by areas of foothill woodland on the perimeter, cut through with riparian forests (bordered by bodies of water such as a river), and the marshes. It is thought that the true Central Valley grasslands ecosystem covered some 13 million acres (5.3 million hectares) before the 18th century, in addition to another 9.5 million acres (3.8 million hectares) of botanically related savanna defined by the presence of scattered valley, blue, and interior live oaks.
Within the Central Valley grasslands today is a unique grasslands feature, a wetland hybrid known as vernal pools. These vernal pools result from several geologic conditions, including clay hardpans, volcanic rock below the topsoil, and the accumulation of alkaline minerals, but they are ecologically unified by the presence of seasonally ponding water during the wet season. This water accumulates in depressions but does not drain to major watercourses or local aquifers due to the geological barriers.
As the water in these pools seasonally evaporates, a series of plants specially adapted to saturated soils germinates, grows, and flowers, resulting in a series of concentric rings of wildflowers. Many of these plants, as well as invertebrates such as fairy shrimp, are restricted to these habitats. The species inhabiting these vernal-pool habitats are as isolated from one another as species occupying different mountain ranges; thus, each vernal pool represents an evolutionarily distinct lineage.
The Central Valley grasslands were once the home of many species of wildlife. Huge herds of tule elk and pronghorn were present, in addition to black-tailed deer, which continue to be important grazers and browsers in the present-day habitat. The apex predator in this ecosystem was the grizzly bear, which once ranged over the foothills, river floodplains, and grasslands in great numbers. It was extirpated (locally extinct) by 1922, however, and the contemporary ecosystem is not conducive to its reintroduction. Mountain lions and coyotes still maintain their role in the Central Valley food web, though coyotes' more-adaptable nature makes them far more ubiquitous in human-modified habitats. The endangered San Joaquin kit fox (Vulpes macrotis mutica) roams the central valley. This unique species is both predator and prey, but is threatened by human pesticides and habitat destruction.
Effects of Human Activity
Before the California Central Valley was settled by humans, the strongly seasonal nature of precipitation in the valley and the resulting pulses in vegetation growth led to moderate grazing during the wet season, followed by migration of grazing ungulates to the surrounding, wetter foothill and montane habitats during the dry season. Native ungulates grazed the Central Valley grasslands seasonally. When the spring rains faded, they migrated into the surrounding woodland and montane habitats. In addition, Native Americans managed this region through the application of prescribed burning.
The native grasslands, however, were simply no match for the changes brought by European settlers. Europeans brought year-round, intensive grazing to the Central Valley. Native perennial bunchgrasses did not evolve with this grazing regime; thus, they succumbed to competition from Eurasian annual grasses, which were introduced in the coats and digestive tracts of imported livestock. Needlegrasses have been replaced by foxtails, filaree, wild oats, and other Eurasian grasses that have almost completely displaced native grasses, to the point that modern Californians have no clue that the golden hillsides that characterize the state in the dry season are the entirely anthropogenic result of human agriculture.
Global warming is predicted to strongly affect the River Valley and its grasslands. In the past, the region experienced about five days of extreme heat, with temperatures above 104 degrees Fahrenheit (40 degrees Celsius). This number has begun to increase and experts predict that in the next thirty years, the area will experience at least thirty days of extreme heat. In 2024, California and its central valley experienced a historic heat wave that created a dangerous situation. These heat waves are predicted to increase in length and frequency. Rising temperatures also greatly increase the risk of wildfires and extreme rain that can cause flooding. Researchers predict that increased precipitation could lead to a near-explosion in the prevalence of local vegetation, resulting in fundamental changes in soil composition, water retention capacity, and biological productivity.
Carrizo Plain, an adjoining valley of the Coast Ranges, has persisted because it is a near-desert habitat unsuitable for most agriculture. It is a critically important habitat. Not only have many plant species managed to maintain their competitive edge against invasive species, but several imperiled animal species have held on as well. Carrizo Plain is the home of the federally endangered San Joaquin kit fox and the giant kangaroo rat, both of which are wholly reliant on the persistence of California Central Valley grasslands habitat. Carrizo Plain, with its roaming pronghorns, snoring spadefoot toads, and other species found nowhere else in California (or the world), is an unimpeachably important resource for international biodiversity conservation.
There are various conservation partners on board to help preserve the grasslands from further change, among them the Bureau of Land Management, Nature Conservancy, California Oak Foundation, and the California Department of Fish and Game. The Nature Conservancy alone identified 385 priority sites in the northern half of the valley.
Bibliography
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Cunningham, Laura. A State of Change: Forgotten Landscapes of California. Berkeley, CA: Heyday, 2010.
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Partida, Jose Pablo Ortiz. "Climate Change Impacts on CA Central Valley: The Warning Shot the US Is Ignoring." The Equation, Union of Concerned Scientists, 16 Dec. 2021, blog.ucsusa.org/pablo-ortiz/climate-change-impacts-on-california-central-valley-the-warning-shot-the-us-is-ignoring/. Accessed 4 Nov. 2024.
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Toohey, Grace and Serna, Joseph. “’Exceptionally Dangerous Situation’: Historic California Heat Wave Putting Millions At Risk.” Los Angeles Times, 3 Jul. 2024, www.latimes.com/california/story/2024-07-03/dangerous-california-heat-wave. Accessed 4 Nov. 2024.