Explain the biological feasibility of the emergence of shrub forms of plants?

During the formation of plant communities, each plant takes its place not only horizontally, but also vertically. Depending on the height of the plant, it belongs to one or another tier. The shrub form is intermediate between lower shrubs and grasses, and taller trees. The variety of plant forms allowed the most efficient use of soil and solar resources. For example, in tropical forests, where conditions for many plants are good, the number and density of layers is much higher than in forests of northern latitude.