Fungi are the third natural kingdom, just as important as animals and flowering plants. As work on the ecology of fungi progresses, we realize that the world of plants is incredibly dependent on fungi in every sense of the word. Fungi break down leaf litter and dead wood and thus ensure that the surface of the world has a fertile layer of soil rather than being a heap of detritus, but it is through the intimate relationship of fungi with the roots of trees and plants, the mycorrhizal relationships, that the most important contribution is made. Trees and woodland live in a symbiotic relationship with a vast number of fungi, and were it not for the help given to the plants through these relationships many, perhaps most, woodland areas would fail. In fact, without the third force of the fungal world, life as we know it would not be possible for plants and thus also impossible for the animal kingdom.