1. Fire
Fire both natural and human induced affects vegetation. It is possible to consider fire abiotic rather than a biotic environment. Fire is a biotic factor to the extent that its occurrences; duration and intensity depend upon the amount of combustible litter and to the extend that most fires started by man. The contrary is true, to the extent that natural fires depend upon lightning and the fire characteristics depend upon climatic and topographic variations. Fire for instance, is controlled by wind. The latter determines the speed and direction of fire. Other climatic factors like humidity and temperature affect the severity of fire. In the East African Savannah, fires are common during the dry season when weather conditions are favourable and combustible litter in plenty. Concentrating on logistic of fire may not/ suffice; its effect on biota. There is a lot of literature, which has been written on fire in the savannah, and any interested reader may investigate.
Some plants need exposure to fire before germination. Fires result in radical changes in the community structure. Some plants have roots and shoots, which are, fire adapters. Fire is usually an occasional factor in the ecosystem, but one, which in a short time can cause substantial modifications. All independent components of ecosystems are likely to be affected by fire, which becomes particularly drastic if driven by wind. Most natural cause of fire is lightening. Fires cause changes in the composition of vegetation and in
soil moisture and nutrient levels. Modifications also occur in microclimates, notably among temperature and light conditions within the vegetation cover, while plant competitors, animal food supplies and habitats are likely to be varied. Fire regarded as most important factor in the origin and development of grassland ecosystem (not necessarily the case). Deliberate burning can be problem, yet exclusion of fire may also
lead to a greater incidence of diseases and pests.
Fire increases plant susceptibility to bacterial and fungal attacks by making scars on them. Such plants can easily be damaged by wind or may attract later fires. Fire kills animals on the surface and those in shallow depths. By destroying habitats, it induces the migration of certain organisms. On the contrary, the creation of open sites attracts seed feeders such as birds and rodents and increases the population of shade intolerants. Fire, like biological variables, has a selective effect. Fire occurrence stimulates populations of species, which are fire resistant plants.
2. Anthropogenic
Human beings are also biotic factors because they select certain plants and animals over others. This is done through agriculture, intensification of grazing and fire. Domestication of animal affects plants differently by grazing and browsing, which results in selection of species, thus affecting the composition of the natural vegetation. Grazing decreases the variety of species in an area, eliminates grasses, shrubs, and bushes, weakens desirable species, and increases competition, survivors and soil fertility decline. Recreation use of natural area, hunting, vehicles, camping also have an impact on landscapes and environment. The spread of domesticated plants, some useful (maize, potato), some harmful species (hyacinth) has been largely due to anthropogenic activities.
3. Time and Ecosystems
A fundamental characteristic of ecosystems is their susceptibility to change with the passage of time. Two kinds of changes take place, each associated with a different time scale: First, ecosystems are modified in a series of stages which cover the lifespan of their component individuals and last for decades or centuries. Second, they are affected by changes, which occur over much longer periods of time, usually measurable in thousands or millions of years, and are a response to alterations in physical environmental conditions together with the evolution of their component species.
francis1897 answered the question on October 11, 2022 at 06:24