Arbuscular mycorrhizal(AM) fungi have significant role for ecosystem structure and function. They are the major component of forest soil ecosystems and critically important for water and nutrient cycling in the system. To understand the ecology of AM fungi the fungal spores were collected, identified and counted in forest soils under various climatic and edaphic conditions. In relation to soil depth 90% of AM fungi spores and mycorrhizas distributed within 15cm soil depth. Number of spores per $100m{ell}$ forest soil volume was 5 to 36 spores from 1 to 3 fungal species. AM fungal species diversity was higher in warmer climates, and more moist and fertile soils. The most frequently found species were Gigaspora decipiens irrespective of soil moisture and Gi. gigantea irrespective of soil fertility. In the Jeju island the soils of Cryptomeria japonica plantations and Miscanthus sinensis var. purpurascens meadow had more AM spores than the other soils. We suggest AM fungi be considered as keystones species when restoring a disturbed forest ecosystem.