Obviously, the forest can be removed if someone chops down all the trees. However, thinning the forest selectively can also push it rapidly past the point where it replenishes itself and maintains the conditions needed for its survival, leading to runaway degredation. Without trees to hold down the soil, erosion washes it into streams. Trees and bushes also slow down runoff water and give it time to infiltrate the soil. Without this effect, floods are more likely, and infiltration decreases, reducing the water table.
Forests also regulate soil temperature and mineral content.
However, if left alone and not irreparably degraded, most lands can revert to forest, with or without human encouragement. Tree plantations can also be established via human effort. These attempts are initially quite vulnerable to animal, insect, or weather attacks, and require a large investment of time and skill. Human uses of and attitudes towards the forest are varied. Often, the damage of human activities is masked by the forests size and extent.