I want to imagine for a minute it is winter. There are pine trees that have survived and even thrived through a "normal" winter, but, not much else. As Spring rolls out and the growth of a forest begins there is an order to that growth.

The first plants to bloom in Spring are the herbaceous layer. The plants, including grasses, that are on the ground. It is more than just grass, it is also what would be called weeds, but, the life of the forest is beginning and the small insects and animals that live among the herbaceous layer begin their lifecycle.

This is the same pattern every year. It begins where water first has accumulated and the sunlight provides for photosynthesis. Every year, the herbaceous layer grows first. 

It is followed by the shrub and bush layer of plants and animals. Then comes the understory of trees. The shorter trees. Then the awakening of the canopy. It is a progression every year that rolls out the same way. There is an order to these communities which provide food, water and sunlight to the forest that will support and protect the animals that live there.

Summer follows with more intense sunlight and ultimately autumn will follow and finally the cold function of winter to end the lives of opportunistic weeds, bacteria, virus, fungus and all the predatory aspects of a forest. Winter and it's depth of cold vary and that variety of weather provides for forest health, REST and protection.