The under story of a forest is a layer made up of young trees short species of trees shrubs and soft stemmed plants.
The under story varies a lot from forest but every where it is darker there is less wind and it is more humid than the canopy above it. The trees are either seedlings struggling to survive or are older trees that have been suppressed by the lack of sunlight.
There are different ways that plants have adapted to live within the forest in the understory competing for sunlight and nutrients. Some grow in the spring or fall when the canopy is not completely covered by leaves. Others have adapted to live with very little or no direct sunlight.
Many birds and animals spend most of their lives in the under story.