The scrub is a vegetal formation characterized by the predominance of shrubs and low-growing trees. This term is applied to different ecosystems, both in temperate and tropical zones. It can be made up of primary or mature vegetation, as well as being a secondary formation product of anthropic intervention.

Its structure can consist of a single stratum of shrubs or have a low tree stratum and a second shrub stratum. The limiting factor is the dry period characteristic of scrub areas.

Catinga in Belo Horizonte (Brazil). Source: Glauco Umbelino from Moro in Belo Horizonte, Brazil

Shrub plants have adapted in various ways, either by shedding their leaves in the dry season or by being sclerophyllous. Another factor that affects its ecology is fire, be it natural or human-caused fires. The soils generally have low fertility, being predominantly sandy and with variations in the geography of the scrubland.

This plant formation is highly variable, but in all types of scrub the common factor is the predominance of the bush biotype and stunted trees. Based on this, there are two general types which are the Mediterranean scrub and the tropical scrub.

The Mediterranean scrub is present on the shores of the Mediterranean Sea basin, as well as the Chilean scrub, the Californian chaparral (USA), the South African fynbo, the kwongan and the Australian mallee.

Within the tropics there are hot climate xerophilous scrub and cold climate high mountain scrub. Among the first are the catinga, the arid chaco, the cardonal-espinar and the African bushes. The scrub or páramo scrub is an example of a cold climate tropical scrub in the high Andean mountains.

The bushes develop in very varied reliefs that go from sea level to 4,000 meters above sea level. These include plains, valleys, and rugged mountainous areas.

The flora varies depending on the geographic area and among the most common families are legumes, ericaceae, myrtaceae and composites. Among the species, the wild olive tree ( Olea europaea var. S ylvestris) in the Mediterranean Sea basin and cacti in the warm tropical scrub stand out.

The main climates in which the scrub develops are the Mediterranean, the warm tropical and the cold tropical high mountains.

The fauna that inhabits the different types of scrub is equally varied, as small mammals such as the Cretan spiny mouse (Acomys minous) can be found in the Mediterranean, as well as elephants (Loxodonta africana) in the African scrub.

Shrubs are not very productive ecosystems, but they have traditionally helped meet the needs of nearby communities. Agricultural, livestock and tourist activities are carried out in them, in addition to extracting raw materials.

Within these plant formations there are protected areas. For example, the Cabo de Gata-Níjar Natural Park (Spain) and the Sus-Masa National Park (Morocco), representatives of the Mediterranean scrub. The Baviaanskloof mega reserve (South Africa) is an example of the fynbos and the Laguna de Mucubají in the Sierra Nevada National Park (Venezuela) includes paramero scrub.

General characteristics

- Origin

Primary scrub

The scrub originates as primary or mature vegetation in environments with certain limitations for plant development.

In some cases there is a sufficient supply of water, but the limiting factor is the soil. Review that there may be soils that can be particularly alkaline, saline or rich in a particular element (eg aluminum).

For other bushes, the limitation is given by extreme temperatures, combined with dry winds (hot or cold).

Secondary scrub

They are areas of degraded forests, either by natural phenomena or by human action. Natural causes include fires (of natural origin), mudslides and landslides.

Anthropic causes include man-made fires and deforestation.

In any case, the primary vegetation cover of the forest (trees, shrubs and grasses) are eliminated from the area. Given this, a natural recovery process begins, as long as the disturbing action ceases.

During the process of natural succession, thickets are initially formed that can then continue to advance until the forest is established again. However, in some cases secondary scrub persists as the definitive vegetation.

The latter happens when the disturbance generated irreversibly affects the environmental balance that allows the forest to exist.

- Vegetation and its structure

The scrub vegetation is sclerophyllous evergreen in temperate and cold zone scrub and deciduous in warm scrub.

An evergreen plant is one that maintains its leaves throughout the year, while deciduous plants lose their leaves in the dry season. Sclerophyllous species have small, stiff leaves with abundant sclerenchymal tissue (lignin).

This type of vegetation tends to be dense, making it difficult for large animals and humans to move around. In addition, it is common for plant species to be thorny in different parts of their body.

Tall scrub

It has a vegetal structure characterized by the abundance of shrubs and low-growing trees. A bush is a woody plant at least in its lower part, branched at the base, with a maximum of 4-5 m in height.

The stocky trees typical of the thicket do not exceed 6-8 m approximately. Therefore, the upper stratum of the shrub reaches between 4 and 8 m in height up to 10 m in the Australian mallee.

The thicket can have a middle layer of shrubs of intermediate size between 1 and 2 m in height. In the lower stratum, grasses and subshrubs are found covering the ground in a discontinuous way.

Medium and low scrub

There are bushes that develop in more extreme environmental conditions, formed by low-growing shrubs and sub-shrubs. In this case, the structure is much simpler, similar to that of a grassland, with practically a single layer.

The height of these thickets ranges from 30-70 cm to 1-2 m, as in the case of the English heaths and also some thickets of the Andes.

- Fire and scrub vegetation

In most scrub ecoregions fire is noted as a shaping factor. In this plant formation, species adapted to survive the action of periodic fires predominate.

Fires can occur by natural causes or by human action (anthropic causes). They cause periodic processes of plant succession so the species present vary.

Adaptations

Among the adaptations of the plants are the underground structures that allow the regrowth after the burning of the aerial part. The presence of suberified bark (with cork) is also common to resist both drought and the action of fire.

- Soil

It is generally poor, predominantly sandy to sandy-loam soils with an abundance of stones. They are generally permeable soils with medium to low moisture retention or limited by alkalinity, acidity or salinity.

However, given the geographic variability of the scrublands, clay and other soils can be found. Thus, in the fynbos (South African scrub) there are complex mosaics of soils in their area of ​​distribution.

The scrub is a category referred to a wide series of plant formations whose common element is the predominance of shrubs. In this sense there are many types, applying local names in each region.

Mediterranean scrub

According to its geographical location and its species composition, at least 5 subtypes of Mediterranean scrub are identified:

Scrub of the Mediterranean Sea coast

It develops along the entire northern coast of the Mediterranean Sea from the Iberian Peninsula to the Middle East. The plant formation reaches its greatest development west of the African Mediterranean coast.

The Mediterranean scrub receives different names such as maquis or maquia (Italy, France), garriga (France), phrygana (Greece), batha (Israel) and tomillar (Spain).

Some of the terms used to refer to the scrub of the Mediterranean coast refer to particular characteristics. For example, the garrigue is a Mediterranean scrub of secondary origin, since it comes from the degradation of the chaparral.

Chilean scrub (Chile)

These are Mediterranean thickets and thorn forests located on the coast and the Central Valley of Chile (Pacific Ocean). In the Cordillera de la Costa they are to the west, between 400 and 1,000 meters above sea level.

Scrub north of Santiago (Chile). Source: Dentren

They are bordered to the east by the Andes Mountains, to the north by the Atacama desert and to the south by the temperate rainforest.

Californian chaparral and coastal sage scrub

Located in the United States and Mexico. The term chaparral comes from the Basque (txaparro) and designates oak or holm oak with its low biotype. The chaparral extends through central and southern California, both in valley areas and in low mountains.

This is a thicket of small trees and shrubs, which reaches a height between 3 and 5 m. In some coastal areas of California there is a low scrub with a predominance of shrubs of the genus Salvia of the Lamiaceae family.

The fynbos (South Africa)

It is the most widespread plant formation in the Cape Town area of ​​South Africa, an area very rich in flora. It consists of a dense thicket formed by low-growing shrubs, in which different associations are distinguished.

The associations depend on the group of predominant species and develop from sea level to 2,000 meters above sea level.

Fynbos in Cape Town (South Africa). Source: S Molteno

In the transition zone to the temperate forest is the fynbos-Virgilia divaricata, an association between the fynbos and forest elements. In this the arboreal species Virgilia divaricata stands out.

The kwongan and the mallee (Australia)

The kwongan is a low scrub of sclerophyllous shrubs (leaves hard from sclerenchymal tissue) that extends across southwestern Western Australia. For its part, the mallee corresponds to eucalyptus thickets located in southern Australia.

- Heathlands

This plant formation is characterized by the presence of small shrubs up to 3 m high called heather (different species of the genus Erica).

The heaths are characteristic of the coast of the Mediterranean Sea and the fynbos, but they can also be found in other places such as Central Europe (Heath or Lande de Lüneburg, Germany) and England (New Forest Heath).

- Warm xerophilous scrub

Catinga

It is a warm dry scrub or chaparral located in the northeast of Brazil, made up of shrubs and stunted trees. It is formed by deciduous plants that in many cases are thorny.

It develops in a bi-seasonal climate, with a wet season from February to May and a dry season the rest of the year. Average temperatures are around 24 to 26 ºC throughout the year, with rainfall of 500 to 700 mm.

Arid chaco

It encompasses extensive plains and mountain ranges in central-western South America, occupying areas of Bolivia, Paraguay and Argentina.

Cardonal-thorn

It is a scrub with a bi-seasonal warm tropical climate, with a predominance of deciduous spiny species that develops in low areas. It is found on the coasts of the mainland and islands of the Caribbean, from sea level to about 600 meters above sea level.

This plant formation is also distributed in the semi-arid plains of the interior in the north of South America, such as the Lara-Falcón depression in Venezuela.

African scrub

Dry scrub of Acacia-Commiphora is found in the Horn of Africa (northern Kenya, southwestern Ethiopia and part of Somalia). It is a gently undulating plain of lake origin (dry lakes and others still existing such as Lake Turkana).

- High mountain tropical scrub: paramero scrub

The páramo is the characteristic biome of the high mountains of the tropical Andes from northern Peru to Venezuela. Its lower limit is the Andean tropical cloud forest and the perpetual snow as its upper limit.

It is a cold semi arid area with high solar radiation, between 3,000 and 4,300 meters above sea level. In this biome several plant formations are differentiated, one of them being the scrub or scrub paramero.

This scrub consists of a set of grasses, subshrubs and shrubs. Its upper stratum from one meter in height to 5 m, depending on the conditions provided by the physiography.

The vegetation formation is lower in open places and higher in the troughs where it is protected from the dry and cold wind.

Relief

The scrub thrives in a wide variety of physiographic conditions, from plains to mountainous slopes. In areas at 0 meters of altitude above sea level up to 4,000 meters above sea level.

Flora

- Mediterranean scrub

Scrub of the Mediterranean Sea coast

Among the species of these bushes, it is worth highlighting the wild olive (Olea europaea var. S ylvestris) which is the wild relative of the olive tree. Other species are the mastic (Pistacia lentiscus) and the myrtle (Myrtus communis).

Wild olive (Olea europaea var. Sylvestris). Source: Pau Cabot

The garrigue is named after the garric (Quercus coccifera), a shrub or little tree up to 6 m high. In turn, on the coast of Andalusia, in Cabo de Gata, the arborescent scrub of the jujube (Ziziphus lotus) is located.

On the African coast we find the succulent thicket of acacias and erguenes on the southwest coast of Morocco. Here you can find the erect or argan (Argania spinosa), various species of Acacia (Leguminosae) and succulent euphorbiaceae.

There are also other species of legumes such as the pegamoscas (Ononis natrix), which also inhabits the Spanish coasts.

Chilean scrub

On the coast are subshrubs such as the coast daisy (Bahia ambrosioides) and the legume Adesmia microphylla. In the valley, there are cacti such as the cyst (Echinopsis chiloensis), bromeliads of the genus Puya and Lithraea caustica (Anacardiaceae).

Likewise, legumes abound, such as hawthorn (Acacia caven), a low-growing deciduous tree.

Californian chaparral and coastal sage scrub

Quercus species (Q. dumosa, Q. berberidifolia) dominate, present as shrubs or small trees 1 to 5 m high. Other species that can be found belong to the genera Salvia, Rhus and Adenostoma mainly.

Fynbos

Proteaceae, ericaceae and restionacea species predominate, the majority with small, fine and rigid evergreen leaves. From this characteristic of the leaves comes the Afrikaner name of Fynbos which means "thin leaves".

The Kwongan and the Mallee

The kwongan is a particular type of scrub that is very diverse in species that extends in sandy plains. In this plant formation the Myrtaceae species predominate with 1268 species.

The second family of plants in number of species are the Fabaceae (Leguminosae) with 1026 species. There are also many species of proteaceae, orchids and ericaceae.

In the kwongan there are numerous endemisms, such as the insectivorous plant Cephalotus follicularis, or the small tree Kingia australis.

Mallee also dominate the Myrtaceae of the genus Eucalyptus (E. albopurpurea, E. angustissima, E. dumosa). Here you can find tall shrubs or small trees up to 10 m high.

- Heathlands

The name of this particular type of scrub comes from the predominance of Erica spp. (Ericaceae).

- Warm tropical scrub

Catinga

Species from the Leguminosae, Bignoniaceae, Asteraceae and Cactaceae families predominate. Among the cacti there are columnar ones like Cereus jamacaru, climbers like Pereskia aculeata or globose like Melocactus bahiensis.

Arid chaco

The chañar (Geoffroea decorticans) is a leguminous tree that grows as a shrub 3-4 m high. Another 1 to 2 m tall shrub that inhabits these thickets is the cashew (Plectrocarpa tetracantha).

In some areas secondary thickets are developed as a result of the anthropic degradation of black locust forests (Prosopis flexuosa). In these thickets, species such as the jarilla (Larrea divaricata), lata (Mimozyganthus carinatus) and the male squiggle (Acacia gilliesi i) dominate.

Cardonal-thorn

In this type of scrub the spiny mimosoid legumes, bignoniaceae and cactaceae predominate. Among the cacti, the orange pitahaya (Acanthocereus tetragonus), buchito (Melocactus curvispinus), Cereus hexagonus and the mezcalito or guajiro cardón (Stenocereus griseus).

African scrub

Legumes are characteristic, especially mimosaceae of the genus Acacia. Various species of Commiphora of the Burseraceae family are also abundant.

- High mountain tropical scrub: paramero scrub

Among the plant species that inhabit it, there are many composites (Asteraceae), of genera such as Pentacalia, Espeletia, Hinterhubera and Culcitium. It is an evergreen sclerophyllous vegetation.

Weather

In general, the scrubland climate is characterized by having a marked dry season and low rainfall. The dry period is relatively long (4 or more months) is the determining factor for the vegetation.

The temperature can vary, being in some cases temperate or cold climates and in others warm. In these ecosystems there is always a significant variation in temperature, be it annual (Mediterranean scrub) or daily (páramo).

- Mediterranean climate

They are characterized by a climate with mild and rainy winters, dry summers (hot or temperate), warm autumns and variable springs. The average temperature remains around 20ºC.

The annual rainfall is variable and in the mountain fynbos it is approximately 200 mm, while in the coastal scrub it reaches 2000 mm.

Geographical occurrence

Mediterranean scrub is found on the shores of the Mediterranean Sea basin, in California (USA), Chile, South Africa and southeastern Australia.

- Warm tropical climate

In the dry African bush the climate is hot and dry for most of the year. Average maximum temperatures are around 30ºC and average minimum temperatures between 18ºC and 21ºC.

There is a short wet season between March and June as the Intercontinental Convergence Zone moves north. Average annual rainfall is between 200 and 400 mm.

In the dry zone of the American tropics we also find a bi-seasonal climate with a rainy season between April and September and a dry season the rest of the year. The average annual temperature is around 27 ºC, with maximum values ​​of 32 ºC and minimum of 22 ºC.

- Cold tropical climate

It is a high mountain tropical climate, with intense ultraviolet radiation and therefore high daytime temperatures. Then at night the temperatures drop extremely, and there may be freezing.

Its peculiar climate has been defined as "winter every night and summer every day." The average temperature is 5-10 ºC, but during the day it can exceed 30 ºC and at night it can be below 0 ºC.

Unlike other areas of scrubland, here the rainfall is high, over 2000 mm per year. Nighttime freezing temperatures and soil permeability decrease available water.

Fauna

- Mediterranean scrub

Scrub of the Mediterranean Sea coast

In the southeastern scrubland of the Iberian Peninsula there is a great diversity of birds. This is because it is an intermediate point in migrations between Africa and Europe.

Here there are species such as the montesina limpet (Galerida theklae) and the Dupont's lark (Chersophilus duponti). Among the reptiles, the black tortoise (Testudo graeca soussensis) inhabits the African coasts.

Wild Cretan goat or kri-kri (Capra aegagrus creticus). Source: Hanay

In the Mediterranean scrub and forests of Crete there are endemic species such as the Cretan spiny mouse (Acomys minous). An endemic species in this area is the wild Cretan goat or kri-kri (Capra aegagrus creticus).

Chilean scrub

There is the culpeo fox (Lycalopex culpaeus) and the cururo (Spalacopus cyanus), a rodent that builds tunnels and feeds on roots and bulbs. Among the birds, the condor (Vultur gryphus) stands out, the largest non-marine bird in the world.

Californian chaparral and coastal sage scrub

Birds such as the Californian cuitlacoche (Toxostoma redivivum) and the speckled scraper (Pipilo maculatus) are frequent.

Fynbos

This thicket has an important diversity of small mammals, birds, reptiles and insects. For example, the lizard called Agama of the southern rocks (Agama atra).

Among the mammals is the small antelope called rockhopper (Oreotragus oreotragus).

Kwongan

Although there are not many animals in this thicket, there are some very interesting ones, such as the honey phalanx or nulbengar (Tarsipes rostratus). It is a very small (6 to 9 cm) marsupial that feeds on nectar and pollen.

- Warm tropical scrub

Catinga

There are many species of birds, highlighting the Lear's Macaw or Indigo Macaw (Anodorhynchus leari), in danger of extinction. It is possible to find other species such as the jaguar (Panthera onca) and the blond capuchin monkey (Sapajus flavius), but in reduced populations.

Arid chaco

It is the habitat of the Argentine puma (Puma concolor cabrerae) and the collared peccary (Pecari tajacu), currently with greatly diminished populations. Likewise, the southern guanaco or southern guanaco (Lama guanicoe guanicoe) inhabits this ecosystem.

Cardonal-thorn

There is the green iguana (Iguana iguana), the turtle or morrocoy (Chelonoidis carbonaria) and the armadillo or cachicamo (Dasypus spp.). Also felines such as the tigrillo or ocelot (Leopardus pardalis) and snakes such as the rattlesnake (Crotalus durissus).

Among the birds, the guacharaca (Ortalis ruficauda) and the turpial (Icterus icterus) stand out.

African scrub

In the region of the Maasai tribe, where savannas and scrubland combine, animal diversity is high. There are herbivores such as the zebra (Equus burchelli and E. grevyi), the oryx beisa (Oryx beisa) and the elephant (Loxodonta africana).

Among the carnivores, the lion (Panthera leo) and the leopard (Panthera pardus) can be mentioned.

- High mountain tropical scrub: paramero scrub

It is part of the habitat of the only South American bear called the Spectacled Bear (Tremarctos ornatus). The condor (Vultur gryphus), had disappeared from these lands but has been successfully reintroduced.

Likewise, the páramo cat (Felis colocolo) and the white-tailed deer (Odocoileus virginianus) are common in these areas.

Economic activities

- Agriculture and Livestock

Crops

In general, scrub areas are not very promising areas for agriculture, however some crops do well. For example, the olive tree (Olea europaea) and various vegetables in Mediterranean scrub areas.

Potatoes are cultivated in the Andean moors, although this activity is highly erosive in this area.

Cattle raising

Being areas of high mountains or poor soils, a high animal load is not developed. However, in many scrubland areas both cattle and goats mainly thrive.

- Extraction of resources from the scrub

The bushes have traditionally been a source of diverse resources for the human communities that inhabit them. These include firewood, wood for different uses such as construction and food.

They also provide industrializable raw material such as the Mediterranean mastic from whose latex an aromatic rubber used in dentistry is made. On the other hand, the common myrtle is used in perfumery.

- Tourism

Tourist activities take place in various protected areas, where natural scrub formations are preserved. In particular, in temperate climates, the flora is abundant and varied, with evergreen vegetation.

These areas, associated in many cases with mountainous and coastal landscapes, are attractive for ecotourism.

The Cabo de Gata-Níjar Natural Park (Andalusia, Spain) is very popular with Spanish and foreign tourists. Likewise, in Kwongan (Australia) ecotourism is promoted by the Kwongan Foundation.

There is also a tourist tradition in the páramo scrubs in Venezuela, for example in the Sierra Nevada National Park.

Examples of scrub in the world

Cabo de Gata-Níjar Natural Park (Spain)

This natural park is located on the coast of Almería in Spain, being of volcanic origin and one of the most arid places in Europe. It includes areas of Mediterranean forest and scrub, as well as other typical ecosystems of the arid coast.

A characteristic formation is the arborescent scrub of Ziziphus lotus, a deciduous shrub. Other associations are the cornicales (Periploca angustifolia) and the lentiscales, the latter formed by the mastic or mata flapper (Pistacia lentiscus).

Sus-Masa National Park (Morocco)

This park shelters an Atlantic coastal strip in southwestern Morocco, which includes a succulent Mediterranean scrub of acacias and erguenes. These thickets include the upright or argan tree (Argania spinosa), Acacia species, and spiny succulent euphorbiaceae.

The upright is a very useful tree in the area, especially for the Berber community. The Berbers use its wood, obtain firewood, and goats browse its leaves.

Baviaanskloof Mega Reserve

It is a group of protected areas that extend through the eastern Cape of Good Hope in South Africa. Among the plant formations under protection is the fynbos, a South African Mediterranean scrub.

In this region the fynbos includes about 7,500 species of plants, of which about 80% are endemic.

Mucubají Lagoon (Venezuela)

It is an area dominated by glacial lagoons, located in the Sierra Nevada National Park in the Mérida state in Venezuela. This area of ​​the park includes two lagoons, the Laguna de Mucubají and the Laguna Negra, at approximately 2,650 meters above sea level.

Mucujabí Lagoon (Venezuela). Source: Cesar Pérez

The route between the two lagoons crosses a pine forest of anthropic origin and different moorland scrub. It is a low to medium scrub, with sclerophyllous shrubs 50 to 3 m high, where species of composites (Asteraceae) predominate.

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