The spring ephemerals bloom first, typically raising their foliage only a few inches above the leaf litter. As they are going dormant the taller ferns, merrybells, and other herbs overtop them. The age of a plant community affects its structure. Young forests have a well-defined shrub layer and understory. The canopy becomes more distinct as the forest ages.
Different forests have different structures.
Deciduous forests have the most elaborate structure, as described above. By contrast, coniferous forests, with their dense stands of tall and narrow trees, typically have very little understory, but can have a dense shrub layer and ground layer of herbs and mosses. Pine forests have the most open canopies of the coniferous forests, with scattered understory trees and a well-defined shrub layer. Ground-layer species are scattered in the sunny openings. Oak woodlands have a structure similar to that of the pine woods, except the trees are smaller in stature and the canopies are wider.