Diverse, Dense and Dominant
Mediterranean shrublands dominate California’s landscapes covering 8.5 % of the state. Globally, they hold more than 20% of the Earth’s plant diversity. Exposure to the sun, temperature, moisture and soil composition all determine what plants live there.
California is 1 of just 5 places in the world with a Mediterranean climate where these shrublands grow. This rare type of climate is characterized by mild, wet winters and dry summers. As a result, California’s growing season occurs in the wet winter, while the dry summers are the dormant season. Temperatures are subtropical with a cold ocean influence that often results in summer fog along the coast. The most prominent plant communities of California’s Mediterranean shrublands are chaparral and coastal sage scrub. Chaparral is dominated by woody shrubs with hard, leathery leaves. Coastal sage scrub consists mainly of low-growing aromatic vegetation with soft foliage.
Dealing with Drought
Coastal sage scrub occupies dry slopes, where the habitat is cooler and drier than chaparral. Rainfall totals under 10 inches (25.4 cm) per year qualifies
it as a desert. Fog, however, causes higher relative humidity and lower temperatures, making scrub vegetation possible.
Coastal scrub plants have 2 strategies for surviving summer drought. Some are drought- deciduous, dropping all their leaves during summer heat to
help reduce moisture loss.
Others withstand summer drought by producing different types of leaves in different seasons. These seasonally dimorphic plants have larger leaves in winter and smaller leaves in the summer. Smaller leaves have less surface area from which to lose water. Scrub plant’s hairy leaves and aromatic oils also help prevent evaporation and reduce the plant’s need for water.
For many, coastal scrub vegetation appears like a weedy wasteland. However, this low- growing vegetation is home to many unique species and is considered endangered.
Coastal scrub is often called “soft chaparral” because many of the dominant plants bend easily or have soft, flexible leaves. The canopy of coastal scrub is not as dense as that of chaparral.
Most plants are less than 6 feet (2 m) tall. The light-colored leaves are full of fragrant oils that evaporate on hot days and cool the leaves.
There are 2 types of coastal scrub. Northern coastal scrub, dominated by stands of coyote brush or bush lupine; and coastal sage scrub, which predominantly consists of fragrant sages. Twenty native species of sage occur in both coastal scrub and chaparral.
The most dominant plants are California sagebrush, black sage and purple-leaved sage.
A shrub with highly aromatic, dark green, narrow triangular leaves. Common on dry slopes, it grows to 6 feet (1.8 m). It gets its name from flower clusters that form dark spheres on the dry stalks after they set seed. It has a strong flavor and California Indians ground the nutritious seeds into meal.
A “true sage” in the mint family, this plant has square stems. The small button-like flower clusters are pale blue to white and flower from April to June.
Sagebrush thrives on steep coastal slopes and rocky ridgetops, where it is exposed to the drying effects of wind and sun. During extreme drought, it may loose all its leaves. This widespread shrub has linear leaves with edges that curl under. It releases chemicals that prevent other species from growing nearby and can re-sprout and produce seeds after a fire.
This aromatic shrub reaches 2-4 feet (61 cm - 1.2 m) in height. Its leaves have a bitter scent and early Californians used it as a flea repellant.
This sage produces 2 types of leaves depending on the season. Winter and spring leaves are larger, softer and less drought-resistant. In the summer, larger leaves are shed to reduce water loss and are replaced by smaller ones. It is a highly prized ingredient in ‘smudge sticks’ originally used by Native Americans.
Often called “bee sage”, the flowers’ strong scent attracts many bees. Hummingbirds, bumble bees and day-flying hawk moths also pollinate white sage.
Between 150 and 200 butterfly species, many endangered, rely on specific Mediterranean shrubland plants to complete their life cycle.
Learn more about the Mission Blue Butterfly >
Shrublands have one of the richest zones of endemic bees in North America. Twenty-one species of scorpions and a large number of spiders have also been described from shrubland communities.
Saving endangered butterfly populations requires replanting their host plants, removing introduced plants and protecting habitat from development and heavy recreational use.
Preservation efforts also include captive breeding and reintroduction programs.
Made in the Shade
Overall, Mediterranean shrublands are hot and dry. Yet chaparral and coastal scrub communities support diverse life.
Animals that live there have similar survival strategies as animals that live in the desert. To conserve energy and water, most avoid the heat of day by staying in shade or by being nocturnal. They remain in burrows until dusk and emerge at night to feed.
As in the desert, many animals, like reptiles and insects, escape the harshest hot, dry season by becoming dormant. Some, like mice and lizards, reduce water loss by secreting a semi-solid urine.
Many shrubland animals survive periodic fires by retreating to underground burrows. After a fire in coastal sage scrub, animals that prefer open area become more common.
Diversity of Shrubland Dwellers
Merriam’s Kangaroo Rat
Kangaroo rats are small, seed-eating rodents adapted for survival in dry environments. Many of the 22 species of kangaroo rats occur only in California. To survive dry desert-like conditions, they get most of their water from the seeds they eat and have specialized kidneys that allow very little output of water. Kangaroo rats hop on their hind feet and use their long tails for balance.
These snakes live in warm, dry habitats and often hibernate in large numbers in rock crevices on south-facing slopes. The are not aggressive and prefer to avoid being seen or heard by potential predators. When they do use their rattle as a warning, tail vibrations can be as fast as 20-100 times per second. A new rattle segment is added each time the snake sheds its skin.
The common poorwill is nocturnal and lives in shrublands, woodlands, chaparral and dry forests where it feeds on insects such as moths, beetles and grasshoppers. It nests on the ground and can survive long cold spells in a dormant state without food and by lowering it body temperature. This adaptation is unique among birds.
Coast Horned Lizard
Coast horned lizards eat a variety of insects, including honeybees, but ants are their favorite food, making up 50% of their diet. They are well-camouflaged and have the ability to change their color to match their background. When threatened, the coast horned lizard can shoot a small stream of blood from its eyes by increasing blood pressure in its head.
Pepsis spp., occur wherever tarantulas are found. Female wasps hunt tarantulas, often entering their burrows to force them out. She paralyzes the tarantula by stinging it and drags it into a burrow where she lays an egg on it and seals the chamber. The immobile, but not dead, tarantula serves as a source of food for the developing wasp larva.
Over 200 species of land snails are native to California. Adapted to dry summers, snails seek shelter and seal off the opening of their shell with a plug to conserve moisture. Rains break their dormancy. Threats to native snails include habitat loss and introduced species.
Drumming up Business
Jerusalem crickets produce calling songs by drumming their abdomen against the soil.
Drumming patterns are very specific to each species. They use the songs to identify members of their species and locate potential mates.
Jerusalem crickets do not have ears and sense vibrations through organs on their legs.
There are only 7 species described from California, but there may be as many as 50 based on their distinctive
Jerusalem crickets are the heaviest insects in California
and can be 1 to 3.5 inches (2.54 - 9 cm) long.
They are found in many habitats including chaparral and coastal sage scrub. They use their large head, mandibles and powerful legs to burrow into the soil.
They are nocturnal and come above ground at night to scavenge for food and search for mates. Their diet includes everything, including dead and live plants and animals.
Jerusalem crickets fill an important niche in ecosystems and are an important food source for coyotes, skunks, opposums and owls. They are the most important food in the endangered Channel Island foxes' diet.
Jerusalem cricket courtship and mating is acrobatic and occasionally fatal for the male.
Males initiate mating by lying next to a female. If she accepts him, she will lie next to him. Jerusalem crickets will maneuver for as long as 20 minutes before mating actually takes place. After mating, the female will sometimes eat her mate as he remains motionless. The reasons for this cannibalism are unclear.
Plants Reclaim the Land
The only plants able to live in chaparral and coastal sage scrub are those that can persist after fire.
Fire may kill everything above the soil, but underground seeds, roots and tubers are unharmed. Seeds with hard coats require fire’s heat to crack open before germinating. In some plants, chemicals or smoke generated by fire encourages germination.
There are two main types of regeneration after fire; re-seeders and re-sprouters. Re-seeders produce new plants from seeds in the soil, while “re-sprouters” produce new plants from underground roots or tubers not damaged by fire.
Re-growth after a fire begins almost immediately as crown-sprouters produce new shoots even before the rains. With the first rains, there is an explosive germination of buried seeds and growth of dormant bulbs. These new plants provide essential ground cover that reduces the amount of soil erosion.
Beating the Heat - Natural Fires Shape Biodiversity
Mediterranean shrublands are some of the most fire-prone vegetation in the world. In California, fire plays an important role in promoting and maintaining diversity in chaparral and coastal sage scrub.
Most natural fires start by lightning strikes and vary in frequency from 10 to 100 years. These periodic fires rejuvenate chaparral by encouraging growth of fire-dependent plants.
Wildfires can occur at any time, but are most frequent in late summer or fall when vegetation is dry. Timing, frequency and intensity of fire are important for germination and survival of shrubland plants.
Maintaining diverse shrublands requires variability in fire frequency. Some plants favor short fire cycles, others require longer cycles to build up seed “banks” in the soil. If fire cycles are too short, there will not be enough seeds to replace plants destroyed by fire. Frequent fires result in shrubland habitat being converted to non-native grassland.
Stands of thick, dark green chaparral against golden hills are one of the state’s most characteristic plant communities and covers 5% of the state. Chaparral grows on steep hillsides with poor, thin soil that cannot support larger plants. The plants tolerate long periods without rain, in dry soil and baking sun.
Most chaparral plants have woody, tough stems with evergreen foliage. The small leaves are thick, leathery and coated with a type of waterproofing that reduces moisture loss and overheating.
These tough evergreen leaves stay on the plant for 2 years before they are replaced. Mature chaparral forms a dense, almost impenetrable thicket of 6 to 9-foot (2 to 3m) tall shrubs. Some chaparral plants produce toxins that inhibit other plants from growing near them.
The shallow roots of chaparral plants extend horizontally to absorb rain. Deeper taproots reach further down to access groundwater. These plants can survive summer drought lasting 5 to 6 months and annual rainfall of only 5 inches (12.7 cm).
Living with Drought
Chaparral plants are adapted to surviving summer drought and fire.
These plants are seldom drought-deciduous. Keeping their evergreen leaves means the plants can photosynthesize year round. Stiff leaves do not wilt, so water is not lost in re-hydrating them. A thick, waxy cuticle or epidermal hairs insulate against heat and cold, preventing water loss and dehydration. Small leaves have less surface area and reduce water loss as well.
Many chaparral plants have fewer stomata on their leaves than other plants. Stomata are openings in the leaves that allow gas exchange for photosynthesis and water loss through evaporation. Researchers think aromatic oils reduce water loss by replacing water in the stomata.
South-facing slopes are hotter and drier than north-facing slopes. These micro-climates create a distinct difference in chaparral species composition. Plants on south-facing slopes have smaller leaves which help reduce moisture loss.
Making a Comeback
Some chaparral plants produce two types of seeds: one germinates under normal conditions, and one requires scarification, or the heat of a fire, in order to germinate. Recent studies suggest that the successful germination of these seeds is determined by both heat and the presence of charcoal from burned wood in the soil.
Many chaparral plants produce flammable oils, alcohols and resins that are deposited into the soil around them. Fire removes these toxins and returns nutrients like nitrogen to the soil. Burning wood releases chemicals into the soil that encourages germination of seeds in the soil.
Some chaparral plants, like manzanita, re-sprout after a fire from underground woody structures called root-crown burls. These structures have buds that remain dormant until the winter rains following a fire. Poison oak and chamise are other chaparral plants that re-grow after a fire by burl-sprouting.
Fire danger is greatest in California at the end of the long, dry summer. Fire accelerates rapidly on steep slopes. Canyons and ridges act to funnel air currents, increasing wind speed and fanning the spread and intensity into a firestorm, which creates its own weather.
Summer Fires + Winter Rains = Mudslides
As hot fires volatize leaf resins, they condense on the soil and form a uniform water repelling layer. Heavy winter rains cause mudslides when water seeps under these layers and washes away entire sections of burned land.
Barking up the Wrong Tree
The smooth, red bark of manzanita may minimize the number of animals and other organisms feeding on it. Trees with thin, smooth bark lack the protection that trees with thick, corky bark, like coast redwoods, have against foraging animals and insects.
Manzanita bark peels away each year which prevents fungi, parasites and epiphytes, such as mosses and lichens, from persisting on the tree's trunk and stems for longer than a year.
The rich, red color comes from tannins in the bark, which are bitter tasting and toxic to some organisms. This may discourage insects, birds, bacteria and other organisms from attacking the plant.
California is the center of diversity for manzanita with about 60 species, many of which are endemic. Several species are rare, threatened or endangered.
Salute to the Sun Manzanita leaves point vertically which reduces the amount of sunlight hitting them and prevents them from drying out. Their thick, leathery leaves also have a waxy surface that resists water loss. Resins from leaves make the soil waterproof, but burrowing worms, rodents and insects turn the soil and help water penetrate.
Chaparral and coastal scrub are California’s most threatened and least protected habitats. Coastal scrub is especially threatened by development and increased use of off-road vehicles.
As land between urban and natural areas diminishes, humans alter natural fire cycles. Human activities are increasing fire frequency to a point where native vegetation cannot recover.
In 1938 President Roosevelt proclaimed the islands of Anacapa and Santa Barbara a national monument.
In 1980, Congress designated 5 of 8 islands lying off California's southern coast as Channel Islands National Park because they possess unique natural and cultural resources.
The Endangered Species Act’s (ESA) listing of the California gnatcatcher made it an umbrella species that protects all coastal sage scrub plants and animals. Located on highly desirable coastal real estate, the eco-region represents the struggle between preservation and human development.
What You Can Do
- Support smart building codes.
- Housing density should be based on fire hazard and topography. Where fuel loads are high and slopes steep, low-density development should be planned.
- To make existing structures fire safe and manage vegetation visit the National Interagency Fire Center: www.firewise.org
- Contribute to organizations preserving open space fire buffers between natural and developed areas.
- Act responsibly when using fire.
- Visit Channel Islands National Park: www.nps.gov/chis