The influence of living organisms is said to be biotic factors. These factors have a profound influence on vegetation not only by their direct interaction but also through their effect on soil and therefore determine the nature of vegetation that can exist in a place.

Biotic factors can be described under the following titles:

1. Influence of plants
2. Influence of insects
3. Influence of wild animals
4. Influence of man and his animals

1. Influence of plants

When vegetation comes up on a site for the first time, plants gradually increase in number and start competing with each other for essential requirements of life, i.e. food and light by desired and/or undesirable species.

Competition between desired species depends on their power to produce abundant seed every year, to disperse it widely, and to germinate and grow even in adverse condition, their rate of growth, moisture requirement, mode of branching, browsing, longevity, fire, etc

Besides desired species, there are some undesirable species affecting the growth of trees of the favored species. Undesirable species may be weeds or harmful species.

Undesirable harmful species may be studied as follows: (i) Parasites (ii) Epiphytes (iii) Climbers (iv) Abnoxiousweeds (v) Fungi

(i) Parasites: Parasites grow on some living plant called host and penetrate their sucking roots into the host plant called hautoria. They do not draw moisture and mineral nutrients from soil. Sanal tree is a root and valuable parasite.Eg. Common parasites-Cuscutareflexa, Cassythafiliformis. Partial parasites-Viscum, Loranthus, Arceuthobium

(ii) Epiphytes: Epiphyte is a plant growing on but not nourished by another plant. They only take the help of other plant in getting access to light. Eg. Ficus bengalensis, F. religiosa, orchids, etc.

(iii) Climbers: A herbaceous or woody plant that climbs up or other support by twinning round them or by holding on to them by tendrils, hooks, aerial roots or other attachments. Large woody climbers in tropical areas are called liana. They depend on other plants for physical support or to get access to light. They damage the trees by killing them or by making groove or by bending the trees. Eg. Bauhinia vahlii, Butea superba, Ipomea, etc.

(iv) Obnoxious weeds: Obnoxious weed reaches in an area and spreads fast. It coppices well and becomes a serious obstacle in the regeneration. For example; Lantana camera, Eupatorium odorantum.

(v) Fungi: A large number of fungi attack forest trees and their attack, besides reducing quality of timber of trees attacked, sometimes change the form and structure of forest communities. They cause damping off in seedlings, wood rot and root rot in poles and trees, thereby killing them or making the timber altogether useless.

2. Influence of insects

Insects are important part of forest ecosystem. But some of them are harmful such as Hoplocerambyx spinicornis(Sal borer), Hapalia machaeralis (Teak defoliator), Hyblea puera (Teak skeletonizer), plecoptera reflexa, Hypsipyla robusta, etc

3. Influence of wild animals

Wild animals are also crucial part of forest ecosystem, which help in pollination of flowers and dispersal of seed. However, they damage the forest crops considerably. For example; Cheetals, Sambars and Nilgai affect on sal regeneration. Porcupines destroy seedlings of bamboo, khair and simal. Pigs, elephants and monkeys damage seedlings samplings and poles by breaking the branches and uprooting them.

4. Influence of man and his animals

Man is responsible for managing forests, yet he continues to be the most powerful agent in destroying forests in many ways. There are some ways of damaging forest vegetation. They are;

• Deforestation and denudation
• Lopping
• Removal of dry leaves
• Collection of flowers and fruits
• Grazing
• Firing
• Encroachment