Why is it necessary to incorporate forest soil along with a forest tree when it is transplanted to a treeless area?

Explanation

Forest trees do not survive well without special fungi that form associations, known as mycorrhizae, with the tree roots. These associations are called endomycorrhizae when the fungal hyphae extend into the root cells, and ectomycorrhizae when the hyphae surround but do not penetrate the roots. In either case,the fungus greatly increases the surface area of the root for the absorption of minerals. In return for supplying the tree with minerals, the fungus receives organic molecules synthesized by the tree. Approximately 90 per cent of all tree species form mycorrhizae and do not grow well without them. When planting a tree where other trees may never have grown, a small amount of forest soil is added to the soil in order to inoculate it with the fungus, which ensures that mycorrhizae develop.