Chaparral is a type of plant community found mainly in California, southern Oregon, and northern Baja California, part of the California floristic province. It is shaped by a Mediterranean climate, which has mild, wet winters and hot, dry summers, as well as rare but intense fires that burn the tops of plants. Many chaparral shrubs have hard, leathery leaves that stay green all year, unlike the nearby coastal sage scrub community, which has softer leaves that fall off during dry periods and is often found on drier, southern-facing slopes.

Three other similar shrubland areas exist in southern Arizona, western Texas, and along the eastern side of central Mexico's mountain ranges. These regions receive summer rains, which differ from the Mediterranean climate found in other chaparral areas.

Etymology

The name is from the Spanish word chaparro, which means "a place where scrub oak grows." The word scrub oak itself comes from the Basque word txapar, which means the same thing.

Overview

In its natural state, chaparral is shaped by fires that happen rarely, with natural fire return intervals between 30 years and over 150 years. Mature chaparral (at least 60 years since the last fire) forms thick, dense growths of plants (except in the more open desert chaparral). These plants are highly flammable during late summer and autumn when the weather is hot and dry. They grow as woody shrubs with thick, leathery, evergreen leaves that are often small. Most of these plants can survive without much water, though some exceptions exist. After a fire, when rain returns, the area is covered by small flowering plants called fire followers, which die back during the dry summer months.

Similar plant communities exist in other Mediterranean climate regions worldwide, such as the Mediterranean Basin (called maquis), central Chile (called matorral), the South African Cape Region (called fynbos), and Western and Southern Australia (called kwongan). According to the California Academy of Sciences, Mediterranean shrubland contains more than 20% of the world's plant diversity. Chaparral covers 9% of California's wildland vegetation and includes 20% of its plant species.

Conservation International and other groups consider chaparral a biodiversity hotspot, meaning it has many different species but is at risk due to human activity.

Chaparral is typically found in areas with steep hills and shallow, rocky soil. Nearby areas with clay soil, even on steep slopes, are more likely to support annual plants and grasses. Some chaparral plants grow in nutrient-poor soils formed over rocks like serpentine, which have high levels of magnesium and iron but low levels of calcium, potassium, and other important nutrients like nitrogen.

California chaparral

The California chaparral and woodlands ecoregion is part of the Mediterranean forests, woodlands, and scrub biome. It has three main sub-ecoregions with different plant communities:

• California coastal sage and chaparral: Found in coastal Southern California and northwestern coastal Baja California, as well as all the Channel Islands off California and Guadalupe Island in Mexico.
• California montane chaparral and woodlands: Located in southern and central coastal and inland areas of California, including parts of the California Coast Ranges, Transverse Ranges, and western slopes of the northern Peninsular Ranges.
• California interior chaparral and woodlands: Found in central interior California around the Central Valley, covering foothills and lower slopes of the northeastern Transverse Ranges and western Sierra Nevada range.

Some plants that grow in the California chaparral and woodlands ecoregion include:
– Oak trees (Quercus species): Coast live oak, scrub oak, canyon live oak, blue oak, and interior live oak.
– Sagebrush (Artemisia species): California sagebrush.
– Manzanitas (Arctostaphylos species): Bigberry manzanita and common manzanita.
– California lilacs (Ceanothus species): Buckbrush and bigpod ceanothus.
– Sumacs (Rhus species): Lemonade berry and sugar bush.
– Buckwheats (Eriogonum species): California buckwheat.
– Sages (Salvia species): Californian black sage.

Another classification system divides the California chaparral and woodlands into two types: cismontane chaparral and transmontane (desert) chaparral.

Cismontane chaparral ("this side of the mountain") grows on the western (coastal) sides of large mountain ranges, such as the western slopes of the Sierra Nevada, Peninsular Ranges, and California Coast Ranges.

In Central and Southern California, chaparral is a major habitat. Plants native to this area, which regrow quickly after fires, include:
– Chamise (Adenostoma fasciculatum)
– Redshanks (Adenostoma sparsifolium)
– Manzanita (Arctostaphylos spp.)
– Ceanothus (Ceanothus spp.)
– Mountain mahogany (Cercocarpus spp.)
– Bush rue (Cneoridium dumosum)
– California buckwheat (Eriogonum fasciculatum)
– Silk-tassel bush (Garrya spp.)
– Yucca (Hesperoyucca whipplei)
– Toyon (Heteromeles arbutifolia)
– Deerweed (Acmispon glaber)
– Laurel sumac (Malosma laurina)
– Wild cucumber (Marah macrocarpus)
– Bush monkeyflower (Mimulus aurantiacus)
– Chaparral pea (Pickeringia montana)
– Hollyleaf cherry (Prunus ilicifolia)
– Scrub oak (Quercus berberidifolia, Quercus dumosa, Quercus wislizenii var. frutescens)
– California coffeeberry (Rhamnus californica)
– Lemonade berry (Rhus integrifolia)
– Sugar bush (Rhus ovata)
– Californian white sage (Salvia apiana)
– Californian black sage (Salvia mellifera)
– Mission manzanita (Xylococcus bicolor)

Chaparral habitats support many animal species. Some birds that live in cismontane chaparral include:
– Wrentit (Chamaea fasciata)
– California thrasher (Toxostoma redivivum)
– California towhee (Melozone crissalis)
– Spotted towhee (Pipilo maculatus)
– California scrub jay (Aphelocoma californica)
– Anna’s hummingbird (Calypte anna)
– Bewick’s wren (Thryomanes bewickii)
– Bushtit (Psaltriparus minimus)
– Costa’s hummingbird (Calypte costae)
– Greater roadrunner (Geococcyx californianus)

Transmontane chaparral, also called desert chaparral, grows on the eastern sides of mountain ranges, in the dry areas behind the mountains. It has a desert climate, not a Mediterranean climate, and is part of the deserts and xeric shrublands biome. Some plants from the California chaparral also grow here. Unlike cismontane chaparral, which has dense plant cover, desert chaparral is more open, with about 50% of the ground covered by plants. Shrubs here can grow up to 10 feet (3 meters) tall.

Desert chaparral is found on the eastern slopes of major mountain ranges near deserts in California, such as the San Bernardino and San Gabriel Mountains in the Mojave Desert and the San Jacinto, Santa Rosa, and Laguna Mountains near the Colorado Desert. It receives less winter rain than cismontane chaparral and has plants with small, tough, evergreen leaves. It grows above desert cactus scrub and below pinyon-juniper woodlands.

Because desert chaparral gets less rain, it is more likely to lose biodiversity and allow non-native plants to grow if disturbed by humans or frequent fires.

Desert chaparral is typically found at lower elevations (3,500–4,500 feet or 1,100–1,400 meters) on the northern slopes of the southern Transverse Ranges and

Fire

Chaparral is a coastal biome with hot, dry summers and mild, rainy winters. This area receives about 38–100 cm (15–39 in) of rainfall each year. Because of this, chaparral is most likely to experience fires during late summer and fall.

The chaparral ecosystem can recover from fires that occur rarely but are very strong. These fires usually happen every 30 to 150 years. Chaparral areas are historically known for their large, intense fires. However, human development near chaparral areas can create problems. Native Americans used to burn chaparral near villages to help grow plants for food and clothing. Before a major fire, chaparral plants like manzanita, chamise (Adenostoma fasciculatum), and Ceanothus species, toyon, and drought-resistant shrubs with tough leaves dominate the area. These plants grow back from underground parts after a fire.

Some chaparral plants, such as chamise, Ceanothus, and fiddleneck, have seeds that can stay dormant in the soil for a long time or wait for fire to germinate. Some chaparral plant communities grow so thick and tall that it is hard for large animals or people to move through them. However, these areas may have many small animals living in the lower parts of the plants. Many chaparral plant seeds germinate after a fire because of heat or chemicals from smoke or burned wood. After a fire, soft-leaved plants like wildflowers and short-lived plants may grow quickly for a few years until the shrubs regrow and form a dense, mature layer. Seeds of these plants remain inactive until a fire creates the right conditions for them to grow.

Some shrubs, like Ceanothus, help add nitrogen to the soil, making more nitrogen available for plants to use.

Because of the hot, dry summers and falls in California, chaparral is one of the most likely places in North America to have fires. Some fires are caused by lightning, but these usually happen when the air is humid and the wind is calm, making them easy to control. Most large wildfires are caused by people during hot, dry Santa Ana winds. These fires are often started by power line failures, car accidents, sparks from machines, arson, or campfires.

Although chaparral plants are adapted to survive fires that happen rarely, frequent fires (less than 10–15 years apart) can destroy them. Frequent fires can eliminate plants that need to grow from seeds, like Manzanita, and change the plant community to one dominated by plants that regrow from underground parts. If fires happen too often over time, even these regrowing plants can be destroyed because they use up their energy reserves. Today, frequent fires caused by accidents can turn chaparral into areas covered with non-native grasses, reducing the number of plant species. This is especially true during droughts caused by climate change.

Invasive plants harm the chaparral ecosystem in many ways. They stop native plants from growing back, increase how often fires happen, and change the chemical makeup of the soil, which makes it harder for native plants to grow. Invasive grasses reduce the amount of nitrogen available to native plants, change the balance of carbon and nitrogen in the soil, create shallow roots, increase plant litter and aboveground growth, and raise soil respiration. Native plants need nitrogen to grow, so when invasive plants take it away, native plants struggle. Invasive grasses also cause more nitrogen to be lost from the soil during fires, making it harder for native shrubs to survive. Invasive grasses have shallow roots that compete with native plants like manzanita, chamise, and Ceanothus. Their shallow roots reduce moisture in the top layer of soil, making it harder for native plants to grow back. More plant litter and aboveground growth can crowd out native plants and change the soil’s quality.

When plant litter decomposes, it adds important nutrients like carbon to the soil. Invasive grasses produce litter with less carbon that is hard to break down. Native shrubs produce litter with more of this hard-to-break-down carbon, which can stay in the soil for centuries. Chaparral helps store carbon in the environment, but invasive grasses reduce this storage and release more carbon into the air after fires.

To fight invasive plants and help fix damaged soil, methods like weeding, planting native species, and hydroseeding can work. Weeding and planting native plants reduce competition after fires and help native plants grow more densely. After fires, levels of carbon and nitrogen in the soil drop, and hydroseeding can help restore these levels. However, hydroseeding might also introduce invasive plants and affect carbon and nitrogen cycles in chaparral areas.

Two older ideas about chaparral fires were widely discussed in the past. Recent research has shown these ideas are not correct:

• Older chaparral plants become unhealthy or unproductive, so fires are needed to keep them healthy.
• Fire suppression policies have caused dead chaparral to build up, leading to larger fires.

The belief that older chaparral is unhealthy may have started in the 1940s when scientists studied how much food was available for deer. However, recent studies show that chaparral can stay productive for a long time without fire. Some chaparral plant seeds need 30 years or more of leaf litter to grow successfully, such as scrub oak, toyon, and holly-leafed cherry. If fires happen less than 10–15 years apart, many chaparral plants are lost, and the area is replaced by non-native grasses.

The idea that older chaparral causes large fires was first suggested in the 1980s by comparing fires in Baja California and southern California. It was thought that stopping fires in southern California let too much fuel build up, causing larger fires. This is similar to what happens in dry pine forests in the U.S. Southwest, where fire suppression has increased forest density. Historically, fires in these forests likely happened every few decades, burning small plants, trees, and logs at low intensity and some trees at high intensity. However, chaparral is different in how it responds to fire.