Ecologically, a wooland is an area covered in trees, differentiated from a forest. In these terms, a forest has a largely closed canopy – the branches and foliage of trees interlock overhead to provide extensive and nearly continuous shade. A woodland, on the other hand, allows sunlight to penetrate between the trees, limiting shade. Woodlands may support an understory of shrubs, herbs, or grasses. Woodlands may form a transition to shrublands under drier conditions.