Chaparral


Chaparral is a shrubland or heathland plant community found primarily in the US state of California and in the northern portion of the Baja California Peninsula, Mexico. It is shaped by a Mediterranean climate and wildfire, 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 below the chaparral biome. Chaparral covers 5% of the state of California, and of the associated Mediterranean shrubland, an additional 3.5%. The name comes from the Portuguese and Spanish word chaparro, for evergreen oak shrubland.

Introduction

In its natural state, chaparral is characterized by infrequent fires, with intervals ranging between 30-50+ years. The fires are high intensity and stand-replacing. Recent human activity has increased fire frequency. The shoots of the Chaparral plants do not have thick bark, therefore, they are not very resistant; however, the vegetative recovery is resilient because its regeneration is rapid from dormant seed banks and root-crowns.
There are two kinds of Chaparral plant species:
Because sprouters can respond with more rapid growth than seeders, they tend to dominate the early years after a fire. If fires become frequent, seeders cannot reach reproductive size before the next fire. System shifts to sprouter-dominance. If fire become even more frequent, sprouters exhaust their below- ground reserves and there will be a conversion to a non-chaparral biome.
Mature chaparral is characterized by nearly impenetrable, dense thickets. These plants are highly 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, and are typically drought resistant. 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, central Chile, the South African Cape Region, and in Western and Southern Australia. According to the California Academy of Sciences, Mediterranean shrubland contains more than 20 percent of the world's plant diversity. The word chaparral is a loan word from Spanish chaparro, meaning both "small" and "dwarf" evergreen 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 – a biological community with a large number of different species – that is under threat by human activity.

California chaparral

California chaparral and woodlands ecoregion

The California chaparral and woodlands ecoregion, of the Mediterranean forests, woodlands, and scrub biome, has three sub-ecoregions with ecosystem—plant community subdivisions:
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:
Another phytogeography system uses two California chaparral and woodlands subdivisions: the cismontane chaparral and the transmontane chaparral.

California cismontane chaparral

Cismontane chaparral refers to the chaparral ecosystem in the Mediterranean forests, woodlands, and scrub biome in California, growing on the western 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
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:
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.
Transmontane chaparral or desert chaparral —transmontane 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. 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 open, with only about 50 percent of the ground covered. Individual shrubs can reach up to in height.
, chaparral in the foreground
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 in the Mojave Desert north and northeast of the Los Angeles basin and Inland Empire; and the northern Peninsular Ranges, which separate the Colorado Desert from lower coastal Southern California. 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 evergreen 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.
Transmontane chaparral distribution
Transmontane chaparral typically grows on the lower northern slopes of the southern Transverse Ranges and on the lower eastern slopes of the Peninsular Ranges. 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.
The California transmontane chaparral is found in the rain shadow deserts of the following:
There is overlap of animals with those of the adjacent desert and pinyon-juniper communities.
Chaparral is a coastal biome with hot, dry summers and mild, rainy winters. The Chaparral area receives about of precipitation a year. This makes the chaparral most vulnerable to fire in the late summer and fall.
The chaparral ecosystem as a whole is adapted to be able to recover from infrequent wildfires ; indeed, chaparral regions are known culturally and historically for their impressive fires. Additionally, Native Americans burned chaparral to promote grasslands for textiles and food. Before a major fire, typical chaparral plant communities are dominated by manzanita, chamise and Ceanothus species, toyon, and other drought-resistant shrubs with hard leaves; these plants resprout from underground burls after a fire. The shoots of these plants are, however, not resistant to chaparral crown-fire regimes as the bark is simply not thick enough. Plants that are long-lived in the seed bank or serotenous 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. Many chaparral plant species require some fire cue for germination. Others, such as annual and herbaceous species like Phacelia require fires to allow sunlight to reach them, and are known as fire followers. During the time shortly after a fire, chaparral communities may contain soft-leaved herbaceuous annual plants that dominate the community for the first few years – until the burl resprouts and seedlings of chaparral perennials create an overstory, blocking the sunlight from other plants in the community. When the overstory regrows, seeds of annuals and smaller plants may lie dormant until the next fire creates the conditions required for germination. Mid-sized plants such as Ceonothus fix nitrogen, while others cannot, which, together with the need for exposure to the sun, creates a symbiotic relationship of the entire community with infrequent fires.
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 very 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. In natural Chaparral communities without human interference, the fires are ignition-prone as there are plenty of ground fuels and the temperatures are fire-permitting during the dry season.
Though adapted to infrequent fires, an increased frequency of fire can modify the community. A moderate frequency of fire will result in the loss of seeder plants such as This moderate frequency disallows seeder plants to reach their reproductive size before the next fire and the community shifts to a sprouter-dominance. High frequency fires can cause the additional loss of sprouters by exhausting their reserves below-ground. Changes in fire frequency can also cause a phenomenon known as disclimax, which is when natural succession of plants is constantly interrupted or arrested at an intermediate stage.
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.

Wildfire debate

There are two assumptions relating to California chaparral fire regimes that appear to 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,
  2. That wildfire suppression policies have allowed dead chaparral to accumulate unnaturally, creating ample fuel for large fires.
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. However, according to recent studies, California chaparral is extraordinarily resilient to very long periods without fire and continues to maintain productive growth throughout pre-fire conditions. Seeds of many chaparral plants actually require 30 years or more worth of accumulated leaf litter before they will successfully germinate. 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.
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 . This is similar to the argument that fire suppression in western United States has allowed ponderosa pine forests to become "overstocked". In the past, surface fires burned through these forests at intervals of anywhere between 4 and 36 years, clearing out the understory and creating a more ecologically balanced system. However, chaparral has a crown-fire regime, meaning that fires consume the entire system whenever they burn, with a historical frequency of 30 to 50 years. In one study, 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. In addition, the number of fires is increasing in step with population growth. Chaparral stand age does not have a significant correlation to its tendency to burn. Low humidity, low fuel moisture, and high winds appear to be the primary factors in determining when and where a chaparral fire occurs and how large it becomes. Fires can be beneficial to plant communities by clearing away canopies of litter, inducing serotenous germination, and sanitizing the soils from pathogens.