Chaparral


Chaparral is a shrubland plant community found primarily in California, southern Oregon, and northern Baja California, part of the California floristic province. It is shaped by a Mediterranean climate and infrequent, high-intensity crown fires. Many chaparral shrubs have 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.
Three other closely related chaparral shrubland systems occur in southern Arizona, western Texas, and along the eastern side of central Mexico's mountain chains, all having summer rains in contrast to the Mediterranean climate of other chaparral formations.

Etymology

The name comes from the Spanish word Quercus coccifera, which translates to "place of the scrub oak". Scrub oak in turn comes from the Basque word txapar, which has the same meaning.

Overview

In its natural state, chaparral is characterized by infrequent fires, with natural fire return intervals ranging between 30 years and over 150 years. Mature chaparral is characterized by nearly impenetrable, dense thickets. 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, evergreen and often small leaves. The plants are typically drought resistant, with some exceptions. 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% of the world's plant diversity. Chaparral comprises 9% of California's wildland vegetation and contains 20% of its plant species.
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 threatened by human activity.
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 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:
Some 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.
  • Wrentit
  • California thrasher
  • California towhee
  • Spotted towhee
  • California scrub jay
  • Anna's hummingbird
  • Bewick's wren
  • Bushtit
  • Costa's hummingbird
  • Greater roadrunner

    California transmontane (desert) chaparral

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 often open, with only about 50% of the ground covered. Individual shrubs can reach up to in height.
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.
Due to the lower annual rainfall 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
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 naturally infrequent, high-intensity fire ; indeed, chaparral regions are known culturally and historically for their impressive fires. Additionally, Native Americans burned chaparral near villages on the coastal plain to promote plant species for textiles and food. Before a major fire, typical chaparral plant communities are dominated by manzanita, chamise Adenostoma fasciculatum and Ceanothus species, toyon, and other drought-resistant shrubs with hard leaves; these plants resprout from underground burls after a fire.
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. 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 of nitrogen compounds in the soil.
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 human-caused fires are commonly ignited by power line failures, vehicle fires and collisions, sparks from machinery, arson, or campfires.

Threatened by high fire frequency

Though adapted to infrequent fires, chaparral plant communities can be eliminated by frequent fires. A high frequency of fire 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.

Invasive species effects on soil composition post and pre fire

Invasive species impact the chaparral ecosystem in many ways; they inhibit the re-establishment of native species, promote shorter term fire frequency, and change chemical composition of soils which ultimately impedes native species success. Annual Invasion on chaparral environments leads to lower levels of readily available Nitrogen for native plants, affects the Carbon-to-Nitrogen ratio, develops shallow fine root systems, creates more litter and aboveground biomass and can increase soil respiration. Native plants rely on nitrogen to grow so when non natives invade they take this away hindering plant growth. High frequency fire due to invasive grasses increase the amount of Nitrogen lost due to volatilization, as nitrogen is lost more consistently native shrubs struggle due to lower than normal nitrogen levels. Non-Native invasive such as grasses tend to have shallower root systems that outcompete natives such as Manzanita, Chamise and Ceanothus. Since invasive grasses root systems are much shallower they reduce soil moisture at the top level of the soil, this greatly reduces the prosperity of re establishing native seedlings. Increased plant litter and biomass aboveground crowd out natives and change desirable soil compositions.
Plant litter when decomposed brings vital nutrients such as Carbon into the below soil. Invasive grasses produce litter with less recalcitrant Carbon in turn resulting in less Carbon intrusion. Recalcitrant carbon is found in higher quantities and quality in native shrubs litter, recalcitrant carbon takes longer to break down and is resistant to decomposing so it can stay in the soil for centuries. Chaparral provides vital carbon sinks for our environment, when invasive grasses move in after short frequency fires we see less carbon storage and more carbon set free into the atmosphere.
To combat these non-native invasions and potentially balance degraded soils, techniques such as weeding and seeding along with hydro seeding can prove effective. Weeding and re seeding native species takes away competition after disturbances and allows native species to increase density. Post fire Carbon and Nitrogen levels greatly decrease and hydro seeding can help bring these levels back to what they were pre fire. Although hydro seeding can help balance these levels it is important to note that hydro seeding does open up the possibility of introducing invasive species and has potential long lasting effects on Carbon and Nitrogen cycles in chaparral ecosystems.

Wildfire debate

There are two older hypotheses relating to California chaparral fire regimes that caused considerable debate in the past within the fields of wildfire ecology and land management. Research over the past two decades have rejected these hypotheses:
  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 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. Historically, mixed-severity fires likely burned through these forests every decade or so, burning understory plants, small trees, and downed logs at low-severity, and patches of trees at high-severity. However, chaparral has a high-intensity 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. 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 and exacerbated by climate change. Chaparral stand age does not have a significant correlation to its tendency to burn.
Large, infrequent, high-intensity wildfires are part of the natural fire regime for California chaparral. Extreme weather conditions, drought, and low fuel moisture are the primary factors in determining how large a chaparral fire becomes.