Forest, plant community, predominantly of trees or other woody vegetation, occupying an extensive area of land. In its natural state, a forest remains in a relatively fixed, self-regulated condition over a long period of time. Climate, soil, and the topography of the region determine the characteristic trees of a forest. In local environments, dominant species of trees are characteristically associated with certain shrubs and herbs. The type of vegetation on the forest floor is influenced by the larger and taller plants, but because low vegetation affects the organic composition of the soil, the influence is reciprocal..