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- Biotic Factors in the wide sense is the interaction between the living organism in its environment.
- These include:-
(a) the interaction between plants,
(b) between the plants and animals and
(c) between the plants and soil micro-flora and micro-fauna
(d) most important is the effect of man on plants.
- Biotic factors also play a major role in determining the present condition and distribution of vegetation types. i.e.
The following are some of the biotic factors:-
2. Wild Animals
5. Domestic Animals
COMPETITION AMONG PLANTS
- Various plants communities react with one another as well as with the habitat in several ways.
In the soil there is competition for water, nutrients and space and the air, it is for light and space.
- Plants affect their habitat by the deposition of humus due to their dead parts.
- Taller plants get much light and carry an increased amount of photosynthesis in comparison to the shaded ones. As a result, the shaded plants do not develop properly and ultimately die.
- In grasslands, desert and cultivated plants competition is chiefly for water and minerals.
- In the forest, light is the most important factor.
- In forests, many plants have solved the problems of getting light by various methods.
TWINERS, CLIMBERS, and LIANES obtain their light by climbing other supporting trees so as to expose their leaves to light.
EPIPHYTES have perched high upon other plants.
- Vigorously growing plants suppress their neighbors.
- Certain undesirable species affect the plant growth. These are weeds, climbers etc.
- Weeds compete with the seedlings of the desired species. The following are some of the Harmful plants found in a Forest.
A parasite is an organism which takes up a part or whole of its nourishment from a host.
Some parasite plants include:
à Cuscuta reflexa
à Cassytha filiformis
à Loranthus longiflours
à Santalum album etc.
à Parasites ultimately cause the death of their host.
These are plants growing on another plant but making their own food. e.g.
à Ficus benghalensis
à F. religiosa
A climber is a plant which climbs up trees by taking their support. e.g.
à Butea superba etc.
A large number of fungi attack the trees of a forest.
(v) ABNOXIOUS WEEDS, e.g.
à Lantana camara
à Cupatorium odoratum etc.
Insect form an integral part of the Ecology of a Forest.
(vii) WILD ANIMALS
à A number of wild animals also cause damage to the forest.
(b) Porcupines feed on the seedling of chir pine.
(c) Black bears like to lick the sap of Deodar, Spruce, and Blue pine, etc.
· Besides Angiospermic parasites, fungi, bacteria, virus, worms, nematodes and other microorganisms and other soil microbes also act as important agents, which alter the physical and chemical properties of the soil, increases or decreases their fertility which has a great impact on the nature and growth of vegetation.
· Among microorganisms Earthworms are most active. Their const and burrowing facilities for soil aeration and drainage. By ingesting mineral matter along with the organic matter Earthworm tends to mix the minerals and organic materials.
· Very often soil microbes such as nematodes, bacteria, and fungi cause diseases in the underground as well as aerial parts of the plants and can cause several destructive diseases.
· Puccinia graminis can cause rust diseases on the wheat.
· Mildews, smut, rust, damping of blight diseases and many others are caused by parasitic fungi.
· Virus too causes mosaic and other diseases in many plants.
i. They are plants are partially Autotrophic.
ii. They grow in the habitat deficient in Nitrogen compounds.
iii. They are not able to synthesize proteins. Therefore they trap small insects, digested and assimilated by the plant tissues. e.g.
§ Pitcher plant
§ Butterwort etc.
§ Cross-pollination of flowers is mostly brought about by insects like Bees, Wasps, Moths, and Butterflies.
§ Some crawling insects like a millipede, snail and other animals like bats, rats, and snakes are responsible for bringing about pollination in flowers.
DISPERSAL OF SEEDS AND FRUITS
§ The seeds of berries, drupes and other small flesh fruits are surrounded by a succulent and juicy cover, they are eaten by birds and other animals and their seeds are dispersed to far-flung areas. (Animal excreta)
§ Earthworms help to tilt and aerate the soil.
§ Fruits of XANTHIUM, CENCHRUS and many others are adapted to cling to the fur animals, who carry these disseminules to some distances before shedding them from their body.
§ Besides large grazing and Browsing animals small organisms and burrowing animals may affect a plant community in numerous ways.
§ Soil bacteria bring about important chemical changes.
§ Protozoa lives on bacteria and fungi, which disintegrated and decomposes dead plants and animals.
§ Caterpillar and locust may devastate the whole area.
§ Burrowing mammals may also have a profound effect on the vegetation.
§ Grazing by wild animals like Deer, Antelope, Giraffe, Zebra etc. do not usually disturb the natural balance of the plant community, because their number is far less than the carrying capacity of the area.
§ On the other hand the domestic animals like Sheep, Goat, Cow etc. usually outnumber the grazing capacity of the area caused injuries and increased unpalatable species.
§ By the trampling, grazing animals adversely affect the aeration of soil, by making it compact and hard and finally render soil unfit for the growth of the trees and shrubs.
§ Grazing animals also destroy the surface layer, followed by erosion and spread of desert.
§ Livestock numbers in Pakistan are increasing by 20% every seven years.
§ Experts are of the view that grazing by domestic animals may be one of the causes for the downfall of Indus civilization.
§ Scientists are of the view that grazing has played an important role in the spread of desert.
§ According to experts, the number of animals that actually graze in Pakistan are least Five times as many as the grazing capacity of the area, that is the reason whey vast scale destruction of vegetation is taking place throughout the country. Thus causing a vast expanse of desert and wastelands.
§ Rodents may destroy a large number of trees.
§ Insects bud eating bird-eating birds, woodpeckers, sparrows, squirrels and other animals cause great harm to the vegetation.
§ Pigs uproot seedlings and damaged shoots.
§ Elephants are very destructive to trees, they break the branches and uproot trees.
§ The insects, birds, squirrel, mice and rodents eat abundant seeds.
§ Some animals eat and destroy seeds at sowing time.
§ The termites are destructive insects for seeds, seedling and standing crops.
§ Fish, ducks and other aquatic animals depends upon the aquatic plants for the food.
§ Lichens are important in weathering of rocks and formation of soil.
§ The seed is brought by migratory birds and colonizing new sites.
§ Biofactor also includes:-
Fire, grazing/browsing, grass cutting, felling, lopping, pruning, Torchwood extraction, Encroachment, Plants, animals, man, insects & microorganisms.
MAN ROLE AS BIOTIC FACTOR
§ Because of his increasing population and scientific advancement, man is changing almost all types of environment.
§ He is destroying vegetation by the excessive and indiscriminate felling of trees for his farmlands, Industries, highways, airfields, Expansion of cities (urbanization).
§ Ruins of Harappa and Moenjodaro are witness to the fact that there used to be good vegetation in the Indus valley in the past.
It is due to miss-management of vegetation that desert conditions prevailed.
§ Mechanical, chemical and biological warfare and frequent use of pesticides, herbicides and weedicides have also played a great role in the destruction of vegetation.
§ Modification of vegetation by FIRE is another biotic effect due to man’s activities.
Crown fires may destroy soil humus and seeds.
§ Man like lower animals, is an important dispersing agent. e.g.
Various types of seeds, fruits and spores
Exotic plants e.g. Poplar, Eucalyptus, Ailanthus, robinia etc.
Improved verities, hybrid etc.
§ Certain species, exotic have proved to be very destructive in the new localities e.g.
introduction of Rabbits in Australia
Tamarix species in America
Prosopis juliflora in Pakistan
Paper mulberry in Pakistan (Islamabad-)
§ Man and domestic animals are affecting the forest in the following manners:-
i. Deforestation and denudation
(a) Improvement in soil and undergrowth so as to facilitate natural Regeneration.
(b) Clearing site for Artificial Regeneration.
(c) Shifting cultivation
(d) Damage to trees
(e) Damage to soil condition
(f) Damage to Regeneration of the area.
(g) Reduction in the productive power of the Forest
(h) Hazard for Wildlife.
iii. Grazing and brousing
v. Collection of dry leaves
vi. Collection of flowers, fruit, seeds and other major and minor forest produce.
§ Man has brought greatest changes in the natural Vegetation in selecting and propagating the desired species.
§ The various effects of man on vegetation character and growth are uncountable.