Chaparral

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This article is about the plant community. For the plant used medicinally, see Larrea tridentata. For other uses, see Chaparral (disambiguation).
Chaparral, Santa Ynez Mountains, near Santa Barbara, California
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Chaparral /ˌʃæp.əˈræl, ˌtʃæp-/[1] is a shrubland plant community found primarily in the U.S. state of California, southern Oregon, and in the northern portion of the Baja California Peninsula, Mexico. It is shaped by a Mediterranean climate (mild, wet winters and hot dry summers) and infrequent, high-intensity crown fires, featuring summer-drought-tolerant plants with hard sclerophyllous evergreen leaves, as contrasted with the associated soft-leaved, drought-deciduous, scrub community of coastal sage scrub, found often on drier, southern facing slopes within the chaparral biome. Three other closely related chaparral shrubland systems occur in central Arizona, western Texas, and along the eastern side of central Mexico's mountain chains (mexical), all having summer rains in contrast to the Mediterraean climate of other chaparral formations. Chaparral comprises 9% of the California's wildland vegetation and contains 20% of its plant species.[2] The name comes from the Spanish word for place of the scrub oak, chaparro.

Introduction[edit]

In its natural state, chaparral is characterized by infrequent fires, with natural fire return intervals ranging between 30 years and over a hundred years.[3] Mature chaparral (at least 50 years since time of last fire) is characterized by nearly impenetrable, dense thickets (except the more open chaparral of the desert). These plants are flammable during the late summer and autumn months when conditions are characteristically hot and dry. They grow as woody shrubs with thick, leathery, and often small leaves, contain green leaves all year (are evergreen), and are typically drought resistant (with some exceptions[4]). After the first rains following a fire, the landscape is dominated by small flowering herbaceous plants, known as fire followers, which die back with the summer dry period.

Similar plant communities are found in the four other Mediterranean climate regions around the world, including the Mediterranean Basin (where it is known as maquis), central Chile (where it is called matorral), the South African Cape Region (known there as fynbos), and in Western and Southern Australia (as kwongan). According to the California Academy of Sciences, Mediterranean shrubland contains more than 20 percent of the world's plant diversity.[5] The word chaparral is a loanword from Spanish chaparro, meaning place of the scrub oak, which itself comes from a Basque word, txapar, that has the same meaning.

Conservation International and other conservation organizations consider chaparral to be a biodiversity hotspot[6] – a biological community with a large number of different species – that is under threat by human activity.

California chaparral[edit]

California chaparral and woodlands ecoregion[edit]

Main article: California chaparral and woodlands
Old-growth chaparral more than a century old
Coastal sage scrub in San Diego County

The California chaparral and woodlands ecoregion, of the Mediterranean forests, woodlands, and scrub biome, has three sub-ecoregions with ecosystem—plant community subdivisions:

Chaparral and woodlands biota[edit]

For the numerous individual plant and animal species found within the California chaparral and woodlands ecoregion, see:

Some of the indicator plants of the California chaparral and woodlands ecoregion include:

Chaparral soils and nutrient composition

Chaparral characteristically is found in areas with steep topography and shallow stony soils, while adjacent areas with clay soils, even where steep, tend to be colonized by annual plants and grasses. Some chaparral species are adapted to nutrient-poor soils developed over serpentine and other ultramafic rock, with a high ratio of magnesium and iron to calcium and potassium, that are also generally low in essential nutrients such as nitrogen.

California cismontane and transmontane chaparral subdivisions[edit]

Another phytogeography system uses two California chaparral and woodlands subdivisions: the cismontane chaparral and the transmontane (desert) chaparral.

California cismontane chaparral[edit]

Cismontane chaparral ("this side of the mountain") refers to the chaparral ecosystem in the Mediterranean forests, woodlands, and scrub biome in California, growing on the western (and coastal) sides of large mountain range systems, such as the western slopes of the Sierra Nevada in the San Joaquin Valley foothills, western slopes of the Peninsular Ranges and California Coast Ranges, and south-southwest slopes of the Transverse Ranges in the Central Coast and Southern California regions.

Cismontane chaparral plant species[edit]
For more flora species, see Category: Natural history of the California chaparral and woodlands.

In Central and Southern California chaparral forms a dominant habitat. Members of the chaparral biota native to California, all of which tend to regrow quickly after fires, include:

An old-growth manzanita, a classic member of the chaparral plant community
Cismontane chaparral bird species[edit]
For more bird species, see Category: Fauna of the California chaparral and woodlands.

The complex ecology of chaparral habitats supports a very large number of animal species. The following is a short list of birds which are an integral part of the cismontane chaparral ecosystems.

Wrentit, the most characteristic bird of the chaparral
Characteristic chaparral bird species include:
Other common chaparral bird species include:

California transmontane (desert) chaparral[edit]

Transmontane chaparral or desert chaparral —transmontane ("the other side of the mountain") chaparral—refers to the desert shrubland habitat and chaparral plant community growing in the rainshadow of these ranges. Transmontane chaparral features xeric desert climate, not Mediterranean climate habitats, and is also referred to as desert chaparral.[7][8] Desert chaparral is a regional ecosystem subset of the deserts and xeric shrublands biome, with some plant species from the California chaparral and woodlands ecoregion. Unlike cismontane chaparral, which forms dense, impenetrable stands of plants, desert chaparral is often open, with only about 50 percent of the ground covered.[9] Individual shrubs can reach up to 10 feet (3.0 m) in height.

Transmontane chaparral in the Laguna Mountains, Cleveland National Forest

Transmontane chaparral or desert chaparral is found on the eastern slopes of major mountain range systems on the western sides of the deserts of California. The mountain systems include the southeastern Transverse Ranges (the San Bernardino and San Gabriel Mountains) in the Mojave Desert north and northeast of the Los Angeles basin and Inland Empire; and the northern Peninsular Ranges (San Jacinto, Santa Rosa, and Laguna Mountains), which separate the Colorado Desert (western Sonoran Desert) from lower coastal Southern California.[9] It is distinguished from the cismontane chaparral found on the coastal side of the mountains, which experiences higher winter rainfall. Naturally, desert chaparral experiences less winter rainfall than cismontane chaparral. Plants in this community are characterized by small, hard (sclerophyllic) evergreen (non-deciduous) leaves. Desert chaparral grows above California's desert cactus scrub plant community and below the pinyon-juniper woodland. It is further distinguished from the deciduous sub-alpine scrub above the pinyon-juniper woodlands on the same side of the Peninsular ranges.

Due to the lower annual rainfall (resulting in slower plant growth rates) when compared to cismontane chaparral, desert chaparral is more vulnerable to biodiversity loss and the invasion of non-native weeds and grasses if disturbed by human activity and frequent fire.

Transmontane chaparral distribution[edit]

Transmontane (desert) chaparral typically grows on the lower (3,500–4,500 feet (1,100–1,400 m) elevation) northern slopes of the southern Transverse Ranges (running east to west in San Bernardino and Los Angeles counties) and on the lower (2,500–3,500 feet (760–1,070 m)) eastern slopes of the Peninsular Ranges (running south to north from lower Baja California to Riverside and Orange counties and the Transverse Ranges).[10] It can also be found in higher-elevation sky islands in the interior of the deserts, such as in the upper New York Mountains within the Mojave National Preserve in the Mojave Desert.[citation needed]

The California transmontane (desert) chaparral is found in the rain shadow deserts of the following:

Transmontane chaparral plants[edit]
Transmontane chaparral animals[edit]

There is overlap of animals with those of the adjacent desert and pinyon-juniper communities.[11]

Fire[edit]

Chaparral is a coastal biome with hot, dry summers and mild, rainy winters. The chaparral area receives about 38–100 cm (15–39 in) of precipitation a year. This makes the chaparral most vulnerable to fire in the late summer and fall.

Chamise (Adenostoma fasciculatum) resprouting after a high-intensity chaparral fire
Wildflower display after the 2007 Witch Creek Fire, San Diego County, CA
Impact of high fire frequency: chaparral/sage scrub type converted to non-native grassland

The chaparral ecosystem as a whole is adapted to be able to recover from naturally infrequent fire (fires occurring a minimum of 30 years apart); indeed, chaparral regions are known culturally and historically for their impressive fires. (This does create a conflict with human development adjacent to and expanding into chaparral systems.) Additionally, Native Americans burned chaparral near villages on the coastal plain to promote grasslands for textiles and food.[12] Before a major fire, typical chaparral plant communities are dominated by manzanita, chamise Adenostoma fasciculatum and Ceanothus species, toyon (which can sometimes be interspersed with scrub oaks), and other drought-resistant shrubs with hard (sclerophyllous) leaves; these plants resprout (see resprouter) from underground burls after a fire.[2]

Plants that are long-lived in the seed bank or serotinous with induced germination after fire include chamise, Ceanothus, and fiddleneck. Some chaparral plant communities may grow so dense and tall that it becomes difficult for large animals and humans to penetrate, but may be teeming with smaller fauna in the understory. The seeds of many chaparral plant species are stimulated to germinate by some fire cue (heat or the chemicals from smoke or charred wood).[2] During the time shortly after a fire, chaparral communities may contain soft-leaved herbaceous, fire following annual wildflowers and short-lived perennials that dominate the community for the first few years – until the burl resprouts and seedlings of chaparral shrub species create a mature, dense overstory. Seeds of annuals and shrubs lie dormant until the next fire creates the conditions needed for germination.

Several shrub species such as Ceanothus fix nitrogen, increasing the availability nitrogen compounds in the soil.[13]

Because of the hot, dry conditions that exist in the California summer and fall, chaparral is one of the most fire-prone plant communities in North America. Some fires are caused by lightning, but these are usually during periods of high humidity and low winds and are easily controlled. Nearly all of the very large wildfires are caused by human activity during periods of hot, dry easterly Santa Ana winds. These man-made fires are commonly caused by power line failures, vehicle fires and collisions, sparks from machinery, arson, or campfires.

Threatened by high fire frequency[edit]

Though adapted to infrequent fires, chaparral plant communities can be eliminated by frequent fires. A high frequency of fire (less than ten years) will result in the loss of obligate seeding shrub species such as Manzanita spp. This high frequency disallows seeder plants to reach their reproductive size before the next fire and the community shifts to a sprouter-dominance. If high frequency fires continue over time, obligate resprouting shrub species can also be eliminated by exhausting their energy reserves below-ground. Today, frequent accidental ignitions can convert chaparral from a native shrubland to non-native annual grassland and drastically reduce species diversity, especially under drought brought about by climate change.[14][15]

Wildfire debate[edit]

There are two assumptions relating to California chaparral fire regimes that have caused considerable debate, and sometimes confusion and controversy, within the fields of wildfire ecology and land management.

  1. That older stands of chaparral become "senescent" or "decadent", thus implying that fire is necessary for the plants to remain healthy,[16]
  2. That wildfire suppression policies have allowed dead chaparral to accumulate unnaturally, creating ample fuel for large fires.[17]

The perspective that older chaparral is unhealthy or unproductive may have originated during the 1940s when studies were conducted measuring the amount of forage available to deer populations in chaparral stands.[18] However, according to recent studies, California chaparral is extraordinarily resilient to very long periods without fire[19] and continues to maintain productive growth throughout pre-fire conditions.[20][21] Seeds of many chaparral plants actually require 30 years or more worth of accumulated leaf litter before they will successfully germinate (e.g., scrub oak, Quercus berberidifolia; toyon, Heteromeles arbutifolia; and holly-leafed cherry, Prunus ilicifolia). When intervals between fires drop below 10 to 15 years, many chaparral species are eliminated and the system is typically replaced by non-native, invasive, weedy grassland.[22][23][24]

The idea that older chaparral is responsible for causing large fires was originally proposed in the 1980s by comparing wildfires in Baja California and southern California. It was suggested that fire suppression activities in southern California allowed more fuel to accumulate, which in turn led to larger fires.[17] This is similar to the observation that fire suppression and other human-caused disturbances in dry, ponderosa pine forests in the Southwest of the United States has unnaturally increased forest density.[25] Historically, mixed-severity fires likely burned through these forests every decade or so,[25] burning understory plants, small trees, and downed logs at low-severity, and patches of trees at high-severity.[26] However, chaparral has a crown-fire regime, meaning that fires consume nearly all the above ground growth whenever they burn, with a historical frequency of 30 to 150 years or more.[3] A detailed analysis of historical fire data concluded that fire suppression activities have been ineffective at excluding fire from southern California chaparral, unlike in ponderosa pine forests.[19] In addition, the number of fires is increasing in step with population growth and exacerbated by human-caused climate change. Chaparral stand age does not have a significant correlation to its tendency to burn.[27]

Large, high-intensity wildfires are part of the natural fire regime for California chaparral.[28] Extreme weather conditions (low humidity, high temperature, high winds), drought, and low fuel moisture are the primary factors in determining how large a chaparral fire becomes.

See also[edit]