Tiger bush, or brousse tigrée in the French language, is a patterned vegetation

community A community is a social unit (a group of people) with a shared socially-significant characteristic, such as place, set of norms, culture, religion, values, customs, or identity. Communities may share a sense of place situated in a given g ...

and ground consisting of alternating bands of

tree In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, e.g., including only woody plants with secondary growth, only ...

shrub A shrub or bush is a small to medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees by their multiple ...

s, or

grass Poaceae ( ), also called Gramineae ( ), is a large and nearly ubiquitous family (biology), family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos, the grasses of natural grassland and spe ...

separated by bare ground or low herb cover, that run roughly parallel to

contour line A contour line (also isoline, isopleth, isoquant or isarithm) of a Function of several real variables, function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value. It is a ...

s of equal elevation. The patterns occur on low slopes in

arid Aridity is the condition of geographical regions which make up approximately 43% of total global available land area, characterized by low annual precipitation, increased temperatures, and limited water availability.Perez-Aguilar, L. Y., Plata ...

and

semi-arid A semi-arid climate, semi-desert climate, or steppe climate is a aridity, dry climate sub-type. It is located on regions that receive precipitation below Evapotranspiration#Potential evapotranspiration, potential evapotranspiration, but not as l ...

regions, such as in

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

Sahel The Sahel region (; ), or Sahelian acacia savanna, is a Biogeography, biogeographical region in Africa. It is the Ecotone, transition zone between the more humid Sudanian savannas to its south and the drier Sahara to the north. The Sahel has a ...

ian West Africa, and

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. Due to the natural water harvesting capacity, many species in tiger bush usually occur only under a higher rainfall regime.

Formation

The alternating pattern arises from the interplay of

hydrological Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and drainage basin sustainability. A practitioner of hydrology is called a hydro ...

ecological Ecology () is the natural science of the relationships among living organisms and their environment. Ecology considers organisms at the individual, population, community, ecosystem, and biosphere levels. Ecology overlaps with the closely re ...

, and

erosion Erosion is the action of surface processes (such as Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...

al phenomena. In the regions where tiger bush is present,

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

growth is water-limited - the shortage of

rainfall Rain is a form of precipitation where water droplets that have condensed from atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. ...

prevents

vegetation Vegetation is an assemblage of plants and the ground cover they provide. It is a general term, without specific reference to particular Taxon, taxa, life forms, structure, Spatial ecology, spatial extent, or any other specific Botany, botanic ...

from covering the entire landscape. Instead, trees and shrubs are able to establish by either tapping

soil moisture Soil moisture is the water content of the soil. It can be expressed in terms of volume or weight. Soil moisture measurement can be based on ''in situ'' probes (e.g., capacitance probes, neutron probes) or remote sensing methods. Water that enters ...

reserves laterally or by sending

root In vascular plants, the roots are the plant organ, organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often bel ...

s to deeper, wetter soil depths. By a combination of

plant litter Plant litter (also leaf litter, tree litter, soil litter, litterfall, or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that has fallen to the ground. This detritus or dead organic material and its constituent ...

, root macropores, and increased surface roughness, infiltration into the

soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...

around the base of these plants is enhanced.

Surface runoff Surface runoff (also known as overland flow or terrestrial runoff) is the unconfined flow of water over the ground surface, in contrast to ''channel runoff'' (or ''stream flow''). It occurs when excess rainwater, stormwater, meltwater, or other ...

arriving at these plants will thus likely to become run-on, and infiltrate into the soil. By contrast, the areas between these larger plants contain a greater portion of bare ground and herbaceous plants. Both bare soil, with its smoother surface and soil crusts, and herbaceous plants, with fewer macropores, inhibit infiltration. This causes much of the rainfall that falls in the inter-canopy areas to flow downslope, and infiltrate beneath the larger plants. The larger plants are in effect harvesting rainfall from the ground immediately up-slope. Although these vegetation patterns may seem very stable through time, such patterning requires specific climatic conditions. For instance, a decrease in rainfall is able to trigger patterning in formerly homogeneous vegetation within a few decades. More water will infiltrate at the up-slope edge of the canopies than down-slope. This favours the establishment and growth of plants at the up-slope edge, and mortality of those down-slope. Differences in growth and mortality across the vegetation band result in the band moving gradually upslope. Tiger bush never develops on moderate to steep slopes, because in these cases surface runoff concentrates into narrow threads or rills instead of flowing over the surface as sheet flow. Sheet flow distributes water more evenly across a hillslope, allowing a continuous vegetation band to form. The exact roles and importance of the different phenomena is still the subject of research, especially of research in physics since the 1990s.

Exploitation and conservation

The woody plants which make up tiger bush are used for fire wood and as a source of foliage for grazers. The extensive loss of tiger bush around

Niamey Niamey () is the capital and largest city of Niger. As the Niamey Urban Community (, CUN), it is a Regions of Niger, first-level division of Niger, surrounded by the Tillabéri Region, in the western part of the country. Niamey lies on the Nige ...

Niger Niger, officially the Republic of the Niger, is a landlocked country in West Africa. It is a unitary state Geography of Niger#Political geography, bordered by Libya to the Libya–Niger border, north-east, Chad to the Chad–Niger border, east ...

, now threatens local

giraffe The giraffe is a large Fauna of Africa, African even-toed ungulate, hoofed mammal belonging to the genus ''Giraffa.'' It is the Largest mammals#Even-toed Ungulates (Artiodactyla), tallest living terrestrial animal and the largest ruminant on ...

populations. In neighbouring

Burkina Faso Burkina Faso is a landlocked country in West Africa, bordered by Mali to the northwest, Niger to the northeast, Benin to the southeast, Togo and Ghana to the south, and Ivory Coast to the southwest. It covers an area of 274,223 km2 (105,87 ...

, the tiger bush vegetation is also declining.

Scientific research

The pattern was first described in 1950 in British Somaliland by W.A. Macfadyen. The term ''tiger bush'' was first coined by Albert Clos-Arceduc in 1956.Albert Clos-Arceduc, « Étude sur photographies aériennes d'une formation végétale sahélienne : la brousse tigrée », Bulletin de l'IFAN, n°spécial, Dakar, 1956, pages 677-684.

Formation

Exploitation and conservation

Scientific research

References

See also