​Various factors influence what kind of a forest will grow in a certain area. The structure of the soil, the availability of nutrients, the amount of sunlight, the variation in temperature, and the amount of rainfall all have an effect in determining what kinds of plants will thrive in a specific place. Because different plants compete for these site factors, a forest contains only the species that have best adapted to its conditions. 

The individuals of a certain species living in a specific area form a population. For example, a stoat population of a certain region consists of all the stoats that live in that region. An organism community of a forest consists of all the different populations of organisms that live in the same forest. A forest ecosystem is the result of the interaction between its organism community and its non-living environment.

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Characteristics of forest ecosystems.