Tiger bush

Last updated
Aerial view of a tiger bush plateau in Niger. Vegetation appears in dark while lighter pixels represent bare soil. The distance between successive vegetated bands varies between 60 and 120 meters. Corona KH-4A satellite reconnaissance system acquired by 1965-12-31. Tiger Bush Niger Corona 1965-12-31.jpg
Aerial view of a tiger bush plateau in Niger. Vegetation appears in dark while lighter pixels represent bare soil. The distance between successive vegetated bands varies between 60 and 120 meters. Corona KH-4A satellite reconnaissance system acquired by 1965-12-31.
Aerial oblique view of a gapped bush plateau in W National Park, Niger. The mean distance between two consecutive gaps is 50 meters Gapped Bush Niger Nicolas Barbier.jpg
Aerial oblique view of a gapped bush plateau in W National Park, Niger. The mean distance between two consecutive gaps is 50 meters
Panoramic view taken from the middle of a bare band in a tiger bush plateau near Batama-Beri, Niger. Altitude decrease from left to right (slope is about one percent). Tiger bush niger.jpg
Panoramic view taken from the middle of a bare band in a tiger bush plateau near Batama-Béri, Niger. Altitude decrease from left to right (slope is about one percent).
Vegetation band in a tiger bush near Zamarkoye, Burkina Faso. Tigerbusch Vegetationsband Marco Schmidt 0773.jpg
Vegetation band in a tiger bush near Zamarkoye, Burkina Faso.
Senescence zone downslope with termite mound. Zamarkoye, Burkina Faso. Tigerbusch Seneszenzzone Marco Schmidt 0785.jpg
Senescence zone downslope with termite mound. Zamarkoye, Burkina Faso.

Tiger bush, or brousse tigrée in the French language, is a patterned vegetation community and ground consisting of alternating bands of trees, shrubs, or grass separated by bare ground or low herb cover, that run roughly parallel to contour lines of equal elevation. The patterns occur on low slopes in arid and semi-arid regions, [1] such as in Australia, Sahelian West Africa, and North America. [2] [3]

Contents

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, ecological, and erosional phenomena. In the regions where tiger bush is present, plant growth is water-limited - the shortage of rainfall prevents vegetation from covering the entire landscape. Instead, trees and shrubs are able to establish by either tapping soil moisture reserves laterally or by sending roots to deeper, wetter soil depths. By a combination of plant litter, root macropores, and increased surface roughness, infiltration into the soil around the base of these plants is enhanced. Surface runoff 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. [4]

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. [5]

More water will infiltrate at the up-slope edge of the canopies than down-slope. [6] 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. [7] [8] [9]

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, Niger, now threatens local giraffe populations. In neighbouring Burkina Faso, the tiger bush vegetation is also declining.

Scientific research

The pattern was first described in 1950 in British Somaliland by W.A. Macfadyen. [10] The term tiger bush was first coined by Albert Clos-Arceduc in 1956. [11]

Related Research Articles

Biome Distinct biological communities that have formed in response to a shared physical climate

A biome is a collection of plants and animals that have common characteristics for the environment they exist in. They can be found over a range of continents. Biomes are distinct biological communities that have formed in response to a shared physical climate. Biome is a broader term than habitat; any biome can comprise a variety of habitats.

Erosion Processes which remove soil and rock from one place on the Earths crust, then transport it to another location where it is deposited

In earth science, erosion is the action of surface processes that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location. Erosion is distinct from weathering which involves no movement. Removal of rock or soil as clastic sediment is referred to as physical or mechanical erosion; this contrasts with chemical erosion, where soil or rock material is removed from an area by dissolution. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres.

Soil erosion

Soil erosion is the displacement of the upper layer of soil; it is a form of soil degradation. This natural process is caused by the dynamic activity of erosive agents, that is, water, ice (glaciers), snow, air (wind), plants, animals, and humans. In accordance with these agents, erosion is sometimes divided into water erosion, glacial erosion, snow erosion, wind (aeolean) erosion, zoogenic erosion and anthropogenic erosion. Soil erosion may be a slow process that continues relatively unnoticed, or it may occur at an alarming rate causing a serious loss of topsoil. The loss of soil from farmland may be reflected in reduced crop production potential, lower surface water quality and damaged drainage networks.Soil erosion could also cause sinkholes.

Geography of Somalia A country located in the Horn of Africa

Somalia is a country located in the Horn of Africa which officially consists of five federal member states, namely Galmudug, Hirshabelle, Jubaland, South West, Puntland and the municipality of Benadir. It is bordered by Ethiopia to the west, Somaliland to the northwest, the Gulf of Aden to the north, the Somali Sea and Guardafui Channel to the east, and Kenya to the southwest. With a land area of 637,657 square kilometers, Somalia's terrain consists mainly of plateaus, plains and highlands. Its coastline is more than 3,333 kilometers in length, the longest of mainland Africa. It has been described as being roughly shaped "like a tilted number seven".

Pedogenesis is the process of soil formation as regulated by the effects of place, environment, and history. Biogeochemical processes act to both create and destroy order (anisotropy) within soils. These alterations lead to the development of layers, termed soil horizons, distinguished by differences in color, structure, texture, and chemistry. These features occur in patterns of soil type distribution, forming in response to differences in soil forming factors.

Regime shifts are large, abrupt, persistent changes in the structure and function of ecosystems, the climate, financial systems or other complex systems. A regime is a characteristic behaviour of a system which is maintained by mutually reinforced processes or feedbacks. Regimes are considered persistent relative to the time period over which the shift occurs. The change of regimes, or the shift, usually occurs when a smooth change in an internal process (feedback) or a single disturbance triggers a completely different system behavior. Although such non-linear changes have been widely studied in different disciplines ranging from atoms to climate dynamics, regime shifts have gained importance in ecology because they can substantially affect the flow of ecosystem services that societies rely upon, such as provision of food, clean water or climate regulation. Moreover, regime shift occurrence is expected to increase as human influence on the planet increases – the Anthropocene – including current trends on human induced climate change and biodiversity loss. When regime shifts are associated with a critical or bifurcation point, they may also be referred to as critical transitions.

Infiltration (hydrology)

Infiltration is the process by which water on the ground surface enters the soil. It is commonly used in both hydrology and soil sciences. The infiltration capacity is defined as the maximum rate of infiltration. It is most often measured in meters per day but can also be measured in other units of distance over time if necessary. The infiltration capacity decreases as the soil moisture content of soils surface layers increases. If the precipitation rate exceeds the infiltration rate, runoff will usually occur unless there is some physical barrier.

Pattern formation Study of how patterns form by self-organization in nature

The science of pattern formation deals with the visible, (statistically) orderly outcomes of self-organization and the common principles behind similar patterns in nature.

Patterned vegetation

Patterned vegetation is a vegetation community that exhibits distinctive and repetitive patterns. Examples of patterned vegetation include fir waves, tiger bush, and string bog. The patterns typically arise from an interplay of phenomena that differentially encourage plant growth or mortality. A coherent pattern arises because there is a strong directional component to these phenomena, such as wind in the case of fir waves, or surface runoff in the case of tiger bush. The regular patterning of some types of vegetation is a striking feature of some landscapes. Patterns can include relatively evenly spaced patches, parallel bands or some intermediate between those two. These patterns in the vegetation can appear without any underlying pattern in soil types, and are thus said to “self-organize” rather than be determined by the environment. Several of the mechanisms underlying patterning of vegetation have been known and studied since at least the middle of the 20th century, however, mathematical models replicating them have only been produced much more recently. Self-organization in spatial patterns is often a result of spatially uniform states becoming unstable through the monotonic growth and amplification of nonuniform perturbations. A well known instability of this kind leads to so-called Turing patterns. These patterns occur at many scales of life, from cellular development to pattern formation on animal pelts to sand dunes and patterned landscapes. In their simplest form models that capture Turing instabilities require two interactions at differing scales: local facilitation and more distant competition. For example, when Sato and Iwasa produced a simple model of fir waves in the Japanese Alps, they assumed that trees exposed to cold winds would suffer mortality from frost damage, but upwind trees would protect nearby downwind trees from wind. Banding appears because the protective boundary layer created by the wind-most trees is eventually disrupted by turbulence, exposing more distant downwind trees to freezing damage once again.

Rill

In hillslope geomorphology, a rill is a shallow channel cut into soil by the erosive action of flowing water. Similar but smaller incised channels are known as microrills; larger incised channels are known as gullies.

Surface runoff Flow of excess rainwater not infiltrating in the ground over its surface

Surface runoff is the flow of water occurring on the ground surface when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the soil is saturated by water to its full capacity, and that the rain arrives more quickly than the soil can absorb it. Surface runoff often occurs because impervious areas do not allow water to soak into the ground. Surface runoff is a major component of the water cycle. It is the primary agent of soil erosion by water. The land area producing runoff that drains to a common point is called a drainage basin.

In hydrology, run-on refers to surface runoff from an external area that flows on to an area of interest. A portion of run-on can infiltrate once it reaches the area of interest. Run-on is common in arid and semi-arid areas with patchy vegetation cover and short but intense thunderstorms. In these environments, surface runoff is usually generated by a failure of rainfall to infiltrate into the ground quickly enough. This is more likely to occur on bare soil, with low infiltration capacity. As runoff flows downslope, it may run-on to ground with higher infiltration capacity and then infiltrate.

Samuel Joseph McNaughton is an American ecologist and professor at Syracuse University. He received his Ph.D. at University of Texas-Austin in 1964, and was tenured to Syracuse University in 1966.

Desert Area of land where little precipitation occurs

A desert is a barren area of landscape where little precipitation occurs and, consequently, living conditions are hostile for plant and animal life. The lack of vegetation exposes the unprotected surface of the ground to the processes of denudation. About one-third of the land surface of the world is arid or semi-arid. This includes much of the polar regions, where little precipitation occurs, and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location.

Land imprinter

The land imprinter is a no-till device for establishing grass cover in arid environments and deserts. The imprinter consists of a metal roller, with steel angles welded to the surface in various configurations. The angled teeth of the imprinter cut through weeds and brush to form a mulch, while the teeth press seeds of grasses and other plants into the soil. The imprints remain stable for approximately two years. During that time, imprints funnel water toward seedlings, protect them from wind, and concentrate nutrients for plant growth.

Alpine vegetation refers to the zone of vegetation between the altitudinal limit for tree growth and the nival zone. Alpine zones in Tasmania can be difficult to classify owing to Tasmania's maritime climate limiting snow lie to short periods and the presence of a tree line that is not clearly defined.

The fungal loop hypothesis suggests that soil fungi in arid ecosystems connect the metabolic activity of plants and biological soil crusts which respond to different soil moisture levels. Compiling diverse evidence such as limited accumulation of soil organic matter, high phenol oxidative and proteolytic enzyme potentials due to microbial activity, and symbioses between plants and fungi, the fungal loop hypothesis suggests that carbon and nutrients are cycled in biotic pools rather than leached or effluxed to the atmosphere during and between pulses of precipitation.

Vegetation classification is the process of classifying and mapping the vegetation over an area of the earth's surface. Vegetation classification is often performed by state based agencies as part of land use, resource and environmental management. Many different methods of vegetation classification have been used. In general, there has been a shift from structural classification used by forestry for the mapping of timber resources, to floristic community mapping for biodiversity management. Whereas older forestry-based schemes considered factors such as height, species and density of the woody canopy, floristic community mapping shifts the emphasis onto ecological factors such as climate, soil type and floristic associations. Classification mapping is usually now done using geographic information systems (GIS) software.

Oak Canyon Nature Center is a nature preserve located in Anaheim, Southern California. Owned by the city, the park spans an area of 58-acres, comprising three adjoining canyons of the Santa Ana foothills. It has an elevation range from 525 to 825 feet ., and contains three major vegetation zones: coastal sage scrub, oak woodland and riparian. Open on weekends, the John J. Collier Interpretive Center features a museum with live animal and regional natural history exhibits.

Bush encroachment

Bush encroachment is a natural phenomenon characterised by the increase in density of woody plants at the expense of the herbaceous layer. It is often considered an ecological regime shift and a symptom of land degradation. Bush encroachment is found to have severe negative consequences on key ecosystem services, especially biodiversity, animal habitat, land productivity and groundwater recharge. Bush encroachment can refer both to the expansion of native plants as well as the invasion and spread of invasive species. The phenomenon is observed across different ecosystems and with different characteristics and intensities globally. Among the more severely affected landscapes is the Veld in Southern Africa.

References

  1. d'Herbès, Jean-Marc; Valentin, Christian; Tongway, David J.; Leprun, Jean-Claude (2001). "Banded Vegetation Patterns and Related Structures". In Tongway, David J.; Valentin, Christian; Seghieri, Josiane (eds.). Banded vegetation patterning in arid and semiarid environments: Ecological Processes and Consequences for Management. Ecological Studies. 149. New York: Springer. pp. 1–19. ISBN   978-1-4613-0207-0.
  2. Deblauwe V., Barbier N., Couteron P., Lejeune O. & Bogaert J. (2008). The global biogeography of semi-arid periodic vegetation patterns. Global Ecol Biogeogr, 17, 715-723.
  3. Valentin, Christian (2004). "Brousse tigrée". In Goudie, A.S. (ed.). Encyclopedia of Geomorphology. pp. 102–103.
  4. Tongway, D. J. & Ludwig, J. A. (2001) Theories on the origins, maintenance, dynamics, and functioning of banded landscapes. Banded vegetation patterning in arid and semiarid environments : ecological processes and consequences for management (ed. by D.J. Tongway & C. Valentin & J. Seghieri), pp 20-31. Springer-Verlag, New York.
  5. Barbier N., Couteron P., Lejoly J., Deblauwe V. & Lejeune O. (2006). Self-organized vegetation patterning as a fingerprint of climate and human impact on semi-arid ecosystems. J Ecol, 94, 537-547.
  6. Galle, S., Brouwer, J. & Delhoume, J. P. (2001) Soil water Balance. Banded vegetation patterning in arid and semiarid environments : ecological processes and consequences for management (ed. by D.J. Tongway & C. Valentin & J. Seghieri), pp 77-104. Springer-Verlag, New York.
  7. Worrall, G. A. (1959) The Butana grass patterns. Journal of Soil Science, 10, 34-53.
  8. Montaña, C. (1992) The colonization of bare areas in two-phase mosaics of an arid ecosystem. Journal of Ecology, 80, 315-327.
  9. Deblauwe, V., et al. (2012). Determinants and dynamics of banded vegetation pattern migration in arid climates. Ecological Monographs, 82(1), 3-21.
  10. Macfadyen W.A. 1950. Vegetation patterns in the semi desert plains of the British Somaliland. Geographic Journal 116: 199-210.
  11. 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.

See also