Tiger bush or brousse tigrée 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,such as in Australia, Sahelian West Africa, and North America.
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. The self-organization of complex spatial patterns can be generated from relatively simple mathematical expressions, often called a Turing pattern. These 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 these models require two interactions at differing scales: local facilitation and more distant antagonism. 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. When there is no directional resource flow across the landscape, regularly spaced patches or spots appear. In contrast, if there is a clear directionality to some important factor, then regularly spaced bands develop perpendicular to the flow. Since then theoretical models have been published documenting a wide variety of patterned landscapes, including: semi-arid “tiger bush”, salt marshes, fog dependent desert vegetation, mires and fens. Although not strictly vegetation, sessile marine invertebrates such as mussels and oysters, have also been shown to form banding patterns.
A community is a social unit with commonality such as norms, religion, values, customs, or identity. Communities may share a sense of place situated in a given geographical area or in virtual space through communication platforms. Durable relations that extend beyond immediate genealogical ties also define a sense of community, important to their identity, practice, and roles in social institutions such as family, home, work, government, society, or humanity at large. Although communities are usually small relative to personal social ties, "community" may also refer to large group affiliations such as national communities, international communities, and virtual communities.
Patterned ground is the distinct and often symmetrical natural pattern of geometric shapes formed by ground material in periglacial regions. Typically found in remote regions of the Arctic, Antarctica, and the Australian outback but also found anywhere that freezing and thawing of soil alternate; patterned ground has also been observed on Mars. The geometric shapes and patterns associated with patterned ground are often mistaken as artistic human creations. The mechanism of the formation of patterned ground had long puzzled scientists but the introduction of computer-generated geological models in the past 20 years has allowed scientists to relate it to frost heaving, the expansion that occurs when wet, fine-grained, and porous soils freeze.
Due to the natural water harvesting capacity, many species in tiger bush usually occur only under a higher rainfall regime.
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.
Hydrology is the scientific study of the movement, distribution, and quality of water on Earth and other planets, including the water cycle, water resources and environmental watershed sustainability. A practitioner of hydrology is a hydrologist, working within the fields of earth or environmental science, physical geography, geology or civil and environmental engineering. Using various analytical methods and scientific techniques, they collect and analyze data to help solve water related problems such as environmental preservation, natural disasters, and water management.
Ecology is a branch of biology that studies the interactions among organisms and their biophysical environment, which includes both biotic and abiotic components. Topics of interest include the biodiversity, distribution, biomass, and populations of organisms, as well as cooperation and competition within and between species. Ecosystems are dynamically interacting systems of organisms, the communities they make up, and the non-living components of their environment. Ecosystem processes, such as primary production, pedogenesis, nutrient cycling, and niche construction, regulate the flux of energy and matter through an environment. These processes are sustained by organisms with specific life history traits.
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. 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 (aeolic) erosion, zoogenic erosion, and anthropogenic erosion. The particulate breakdown of rock or soil into 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 its dissolving into a solvent, followed by the flow away of that solution. Eroded sediment or solutes may be transported just a few millimetres, or for thousands of kilometres.
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.
Soil crusts are soil surface layers that are distinct from the rest of the bulk soil, often hardened with a platy surface. Depending on the manner of formation, soil crusts can be biological or physical. Biological soil crusts are formed by communities of microorganisms that live on the soil surface whereas physical crusts are formed by physical impact such as that of raindrops.
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.
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.
The exact roles and importance of the different phenomena is still the subject of research.
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.
Desertification is a type of land degradation in which a relatively dry area of land becomes a desert, typically losing its bodies of water as well as vegetation and wildlife. It is caused by a variety of factors, such as through climate change and through the overexploitation of soil through human activity. When deserts appear automatically over the natural course of a planet's life cycle, then it can be called a natural phenomenon; however, when deserts emerge due to the rampant and unchecked depletion of nutrients in soil that are essential for it to remain arable, then a virtual "soil death" can be spoken of, which traces its cause back to human overexploitation. Desertification is a significant global ecological and environmental problem with far reaching consequences on socio-economic and political conditions.
Soil erosion is the displacement of the upper layer of soil, it is one 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.
Ecological succession is the process of change in the species structure of an ecological community over time. The time scale can be decades, or even millions of years after a mass extinction.
A phreatophyte is a deep-rooted plant that obtains a significant portion of the water that it needs from the phreatic zone or the capillary fringe above the phreatic zone. Phreatophytes are plants that are supplied with surface water and often have their roots constantly in touch with moisture. A phreatophyte is one that absorbs its water from a constant source on the ground. They can usually be found along streams where there is a steady flow of surface or groundwater in areas where the water table is near the surface.
In ecology, regime shifts are large, abrupt, persistent changes in the structure and function of a system. 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.
Xerosere is a plant succession that is limited by water availability. It includes the different stages in a xerarch succession. Xerarch succession of ecological communities originated in extremely dry situation such as sand deserts, sand dunes, salt deserts, rock deserts etc. A xerosere may include lithoseres and psammoseres.
The science of pattern formation deals with the visible, (statistically) orderly outcomes of self-organization and the common principles behind similar patterns in nature.
Surface runoff is the flow of water that occurs when excess stormwater, meltwater, or other sources flow over the Earth's surface. This can occur when the soil is saturated to full capacity, and rain arrives more quickly than 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.
In soil, macropores are defined as cavities that are larger than 75 μm. Functionally, pores of this size host preferential soil solution flow and rapid transport of solutes and colloids. Macropores increase the hydraulic conductivity of soil, allowing water to infiltrate and drain quickly, and shallow groundwater to move relatively rapidly via lateral flow. In soil, macropores are created by plant roots, soil cracks, soil fauna, and by aggregation of soil particles into peds.
Dryland salinity is a natural process for soil, just like other processes such as wind erosion. Salinity degrades land by an increase in soil salt concentration in the environment, watercourse or soil in unirrigated landscapes, being in excess of normal soil salt concentrations in dryland regions.
In hydrology, oasification is the antonym to desertification by soil erosion; this technique has limited application and is normally considered for much smaller areas than those threatened by desertification.
Vegetation and slope stability are interrelated by the ability of the plant life growing on slopes to both promote and hinder the stability of the slope. The relationship is a complex combination of the type of soil, the rainfall regime, the plant species present, the slope aspect, and the steepness of the slope. Knowledge of the underlying slope stability as a function of the soil type, its age, horizon development, compaction, and other impacts is a major underlying aspect of understanding how vegetation can alter the stability of the slope. There are four major ways in which vegetation influences slope stability: wind throwing, the removal of water, mass of vegetation (surcharge), and mechanical reinforcement of roots.
Wildfires consume live and dead fuels, destabilize physical and ecological landscapes, and impact human social and economic systems. Post-fire seeding was initially used to stabilize soils. More recently it is being used to recover post wildfire plant species, manage invasive non-native plant populations and establish valued vegetation compositions.
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.
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.