California chaparral and woodlands

• Category: Forest Biomes.
• Geographic Location: North America.
• Summary: California's chaparral and woodlands are interrelated ecoystems that form the heart of the mediterranean climate-influenced Pacific coast of North America.

The cold waters of the Pacific Ocean, high pressure from descending tropical air masses, mountain uplift from colliding tectonic plates, and numerous other forces combine on North America's west coast to create the temperate, rainy winters and hot dry summers that define California's mediterranean climate. This regime has favored the development of the biodiverse oak-dominated woodlands and fire-dependent chaparral (scrublands) that compose the classic rural California landscape, and also provided an attractive environment for human settlement for millennia.

Although they are structurally and botanically quite different, California's woodlands and chaparral are largely influenced by the same broad-scale climatic variables. In fact, they can often be found within a few dozen feet of each other. Perhaps nowhere in North America is the effect of slope aspect more profound than in lower and middle elevations of the Coast Ranges, Sierra Nevada, Peninsular, and Transverse Ranges of California. The south and west faces of these mountains receive much more solar radiation during the hottest parts of the day at the hottest time of the year, leading to higher drought stress on these often-chaparral-covered slopes. The opposing north and east slopes are comparatively cool and moist, and often contain woodlands. Adding to this contrast is the presence of riparian (water area) corridors between the mountains, rich in cottonwoods, willows, and even coast redwoods.

Woodlands

There are many geographic varieties of California woodlands, most of which are dominated by one or more species of oak. Among these, the most widely distributed is the habitat known as foothill woodland, which forms a continuous ring around the Great Central Valley and covers approximately 10 million acres (4 million hectares). Dominant trees in foothill woodland can include the evergreen interior live oak and the deciduous blue oak and valley oak, depending on the microclimate. The foothill pine, often interspersed with oaks in this habitat, has a distinctively bushy or branched appearance compared with most conifers, resulting from the open nature of the habitat in which it grows.

Much of the foothill woodland could more correctly be classified as savanna. On the flatlands of the peninsular ranges of Southern California are similar open woodlands of Engelmann oak; on the Pacific slope of the Coast Ranges, the woodlands are dominated by coast live oak. The climate of these coast-live-oak woodlands is influenced by the moderating influence of the ocean; thus, they may form denser, more forest-like stands. In areas influenced by frequent fog, they are often draped in beards of lace lichen, lending a Tolkienesque aesthetic to these forests.

Chaparral

Interspersed with these woodlands are expanses of scrubland or chaparral. This dry, or xeric, environment is home to shrubs that have evolved to be drought-tolerant in a variety of ways. Many have waxy or hair-covered leaves to reduce water loss. This adaptation allows them to continue photosynthesizing in the height of summer, unlike drought-deciduous shrubs in neighboring ecosystems. Some, such as many species of manzanita, have leaves with an up-and-down orientation to reduce direct sun exposure. On the more mesic, or wetter, slopes, short-statured scrub oak dominates the chaparral.

Chaparral is strongly fire-dependent; shrubs here have evolved to survive in this fire-prone environment in different ways. Chamise, one of the most common chaparral shrubs, quickly resprouts after a fire from a root ball known as a burl. It also exudes volatile chemicals in the height of summer, suggesting that it actively encourages fire. It is thought that fires cause a depletion of nitrogen in the soil, which may also favor shrubs such as Southern California lilacs (Ceonothus spp.), which can fix atmospheric nitrogen for their own growth. Unlike chamise, Ceonothus cannot resprout if the aboveground plant is killed by fire, but it survives in fire-stimulated seed banks.

Characteristic Animals

Because these habitats often occur quite close to each other, they share many species of animal wildlife. Mule deer are common in both California woodlands and chaparral; in fact, they can become so locally abundant that their browsing can have strongly negative effects on oak regeneration. These deer are the primary prey of mountain lions, the apex predator of this ecosystem. The range of this ecologically flexible cat extends from Canada to South America. Black bears also are common there, though they are far more omnivorous than the strictly carnivorous mountain lion. The habitat once was home to the much larger grizzly bear, but California's last wild grizzly was killed in 1922, and now is present only on the state flag.

California chaparral and woodland habitats are home to a diverse range of smaller mammals, including two species of woodrats or packrats, so named because they have a habit of collecting objects such as sticks, pine cones, bottle caps, and house keys. They stack these objects in their dens in piles known as middens. In some drier areas, middens have been preserved as subfossils and used to research climates thousands of years in the past.

Characteristic birds of the woodlands and chaparral include the raucous and wily scrub jay and the ever-busy acorn woodpecker. In the damp, dark areas underneath fallen logs, one can find the Ensatina salamander, a morphologically diverse group of amphibians. This is the textbook example of ring species, whose members are diverging or have diverged into different species around a central barrier to gene flow—in this case, the Great Central Valley. Flipping over a few more logs is likely to reveal some of the many snakes that make their home in this environment, including the western rattlesnake and its nonvenomous, visually striking predator, the California kingsnake. The chaparral also is home to the diminutive ring-necked snake, which has an olive body, yellow–red neck, and bright orange belly.

Human Activity

These habitats have been used by humans for thousands of years. The oak tree's fruit, the acorn, was a particularly important food source for Native Americans in this region. There are many easily accessible grinding rock sites in the foothill woodlands, where people such as the Miwok and Maidu, among others, ground their acorns into meal for countless generations.

Native Americans manipulated the landscape to suit their needs through the use of burning; these ecosystems have faced far more pervasive changes since European settlement. As in many ecosystems, nonnative species are a significant concern, with Eurasian brome grasses and star thistle crowding out native grasses and forbs in the open woodlands. Cattle browse and trample regenerating vegetation. Wild pigs are particularly voracious consumers of acorns, causing sharp declines in young blue oak trees in much of the Coast Ranges.

Agricultural land use has caused habitat loss; California's rightfully famous wine country is largely in the foothill woodland ecosystem. The chaparral of southern California has been particularly hard hit by development, and much of the acreage that has not been converted to cities has had its natural fire cycle disrupted because of fire suppression to protect adjacent subdivisions.

Fortunately, these threats are recognized, and active conservation initiatives are in place to preserve California woodlands and chaparral for future generations. These initiatives include the U.S. Fish and Wildlife Service's California Foothill Legacy Area. It is a far-reaching project, begun in 2011, that seeks to protect working rangelands and woodland by buying easements on the property, allowing the land to continue to be used for things such as grazing while protecting it from residential or commercial development.

Global warming effects on the oak savanna and chaparral of California are difficult to predict, as the biome has evolved in a complex manner that already accommodates extreme weather events, high winds, and great local divergence in temperature and moisture. These built-in factors mean that even if more extreme rainfall and drought events occur, or the arrival of Santa Ana winds later in the season, become more typical, it is not clear that this biome will be more than marginally disrupted. However, some experts predict that climate change will have negative effects on the area such as physiological stress, canopy thinning, loss of vegetation, and an increase in wildfires. One of the biggest concerns is the increase of fires due to extended fire season and the occurence of larger fires. Fragmentation of habitat is also a threat, as efforts to retain intact areas of habitat will have to take into account the likelihood of more extreme fluctuations in climate patterns.

Bibliography

Barbour, Michael, Bruce Pavlick, Frank Drysdale, and Susan Lindstrom. California's Changing Landscapes. Sacramento, CA: California Native Plant Society, 1992.

“Climate Change Trends for California’s Chaparral Ecosystem.” United States Forest Services, 2018, research.fs.usda.gov/pnw/news/highlights/climate-change-trends-californias-chaparral-ecosystem. Accessed 11 Nov. 2024.

Johnston, Verna R., and Carla J. Simmons. California Forests and Woodlands: A Natural History. Berkeley: University of California Press, 1996.

Pavlick, Bruce M., Pamela C. Muick, Sharon Johnson, and Marjorie Popper. Oaks of California. Los Olivos, CA: Cachuma Press, 1991.

Schoenherr, Allan A. A Natural History of California. Berkeley, CA: University of California Press, 1992.

Storey, Emanuel A., et al. "Evaluating Drought Impact on Postfire Recovery of Chaparral Across Southern California." Ecosystems, 19 Oct. 2020, doi.org/10.1007%2Fs10021-020-00551-2. Accessed 11 Nov. 024.

U.S. Fish and Wildlife Service. “California Foothills Legacy Area Proposal.” 2012. . Accessed 11 Nov. 2024.