(i) Nudation
This is the initiation of the succession by a major disturbance in the environment. It is described as the emergence of barren environment, free of vegetation e.g. exposed sand. Such sites may result from volcanic action remnants of glacier movement.
The substrate therein is virtually lifeless and can at best sustain only autotrophic (organism capable of creating its own food from inorganic substances) bacteria.
Through bio-chemical processes, nudation establishes abiotic environment suitable for future colonization. Lichens, for instance, secrete weak acids which in turn break down rocks into less developed soil, the initial medium for the development of early colonizers.
(ii) Migration
Without any pre-existing seeds or root systems in the soil, organisms must migrate into the new environment from other areas. Migration, also known as dispersal, involves arrival of the early colonizers (rapidly dispersing species) to the new habitat and occurs at different rates because colonizing species differ in dispersal (migration) ability.
First to arrive are early colonizing species (e.g. lichens and certain mosses) which are introduced into the environment through dispersion. The decomposition of these colonizing species aids in soil development, adding organic matter. The formation of many plants is retarded until soil development has occurred (including the formation of sand, silt, clay; organic matter).
The early colonizers are also called R-Selected Species which have great dispersal mechanisms are high reproductive rates. Examples include annual plants.
(iii) Ecesis
Although migration continually occurs, the establishment or subsequent ability of the seeds to germinate, grow and reproduce successfully of plant species is dependent upon soil formation and development. Allogenic mechanisms- i.e. changes in ecosystem from only abiotic influences leads to ecesis, which is defined as the successful establishment of a plant or animal species in a habitat. This occurs as a result of these abiotic influences such as erosion: and gradual removal of harmful substances from the soil by natural processes. After dispersal, the early colonizers establish themselves at the site, undergoing maturation and reproduction.
The Ecesis stage consists of proliferation of early colonizers through germination, growth, and reproduction. It marks the point in succession during which early colonizers (pioneer species) survive their dispersal. At the dunes, early colonizers such as the marram grass (ammophila breviligulata) fully develop, thriving on the dry soil. Different maturation rates among colonizers allow for the gradual ecesis of differnt species to temporarily gain an advantage over other organisms.
(iv) Competition:
This is the struggle of species for the available resources (e.g. nutrients, water, light, space). Some plants are eliminated; whereas the most competitive plants are adapted. It is basically what decreases accessibility of the same resources for another individual and arises between both intra- and interspecific organisms in the community. Intraspecific competition occurs when individuals of the same species compete while interspecific competition occurs when individuals of 2 Or more species in a community compete for the same/similar limiting resources.
(iv) Reaction
Reaction simply refers to the adjustment of the environment by the organism. It consists of autogenic succession which is the transformation of environment caused by the plants themselves. The process results from early colonizers which clear the way for the later more mature species.
Abundance of pioneer species affects abiotic environment by changing local conditions, for instance, when the leaves of alders (deciduous shrub or tree) decompose, the pH of soil drops. The change in pH allows the entry of conifer trees, which require acidic soil.
(v) Stabilization
The different ecological processes see mature communities achieve equilibrium. This is defined as a generally stable and productive population in which biological potential is reached and one form of vegetation dominates.
Stable plant community is, for instance, marked by both deciduous and coniferous forests with mosses, herbaceous species and shrubs on the under story. Such community may be at the climax stage where two or more plant species predominate. This stage manifested in mature species pervading over the more primitive pioneer species.
(vi) The Concept of Climax Community
The climax community is the last stage of an ecological succession of communities arid manifests the most stable condition within a succession, stable vegetation being in equilibrium with its environment. According to the mono climax theory of Clements 1916, the climax formation is mainly controlled by vegetation factors. Therefore a climax community is not affected by other environmental factors such as soil or topography. Stabilization may in fact be an illusion. A degree of instability is characteristic of communities because' of climatic change, and the continuing nature of evolutionary process. Environmental factors are not constant and climate although an, important factor does not influence the vegetation ', communities on its own.
The linkage between climate; vegetation and soils best demonstrates the interaction and interrelations between the atmosphere, biosphere and lithosphere. Vegetation that has evolved! in response to the average climatic conditions of a region as well as its occasional temperature and moisture extremes is called Natural Vegetation. Energy availability is crucial in determining natural vegetation at higher latitudes, whereas moisture supply is more important j at lower latitudes. In sub-humid climates grasslands are predominant, while in humid climates j the natural vegetation is usually forest. In polar and sub-arctic climates, where solar energy j input-is more critical than moisture, the tundra vegetation is tundra. Vegetation in widely separated regions with similar climates has been-known to evolve similar characteristics. Therefore major vegetation regions of the world correspond to climatic regions of the world.
Similarly on a global scale, major soil types show a close relationship to climatic zones. The energy and moisture delivered by the atmosphere influence many aspects of soil formation, these include translocation, the rates of chemical reactions, and organic activity in the soil, abundant rainfall aids translocation, and warm and wet conditions favour chemical reactions and organic activity. Both vegetative production and the activity of soil bacteria and other larger organisms are curtailed in desert and tundra regions and enhanced in humid tropical regions. In dry desert environment, both plant litter and soil organisms are minimal, and in the tundra organic litter decays slowly, often forming acidic peat. Plant production is at a maximum in the warm and wet tropics, but here the destruction of litter by organisms is so rapid and thorough that the soil is actually poor in organic matter.
Climate affects the chemistry of soil moisture, which in turn affects the solubility of various substances in the soil For example iron can be removed only by acidic water. Soil water tends to be acidic in cool wet areas, which are normally covered by coniferous forest. Therefore iron is leached from the topsoil profiles in such areas. In dry regions lime leached from the upper portion, of the soil, is re-deposited at a lower level where the moisture evaporates rather than moving through the water table.
Many soils contain features formed thousands of years ago under different environmental conditions. Such remnant features are important indicators of past climates and vegetation, and have given evidence of shifts in climatic boundaries. Soils also reflect expansion and contraction of the world's deserts, as well as less severe climatic fluctuations in nearly all parts of the world.
francis1897 answered the question on February 27, 2023 at 12:48