The soil is also a dynamic system that has developed in response to the interactions between the four spheres. Soils are a critical component of terrestrial ecosystems providing storage pools for nutrients, water, and air, and a medium of support (i.e., root anchoring) for terrestrial plant. Many important processes related to nutrient cycling occur in the soil and the productivity of a particular ecosystem is intimately linked to the quality of the soil. Equally important, soils provide resiliency to terrestrial ecosystems, buffering the impacts of anthropogenic perturbations (e.g., acid deposition, clearcutting) and allowing ecosystems to quickly recover following catastrophic natural perturbations (e.g., forest fires, insect attacks, volcanic eruptions).