The study, carried out in the ash (Fraxinus excelsior L.) stands, reveals that this species is distributed from lowlands to uplands (sub-Alpine) and from western to eastern parts of the Caspian forests and is well adapted to semi-humid to very humid climates with mild to very cold winters. Ash grows well on rich to relatively rich, humid with well to poor drainage, acidic to alkaline and silty loam to clay – loam soils and on different parent materials. So, it is found on various soil types such as gley, pseudogley, brown (forest br., washed br., acidic br., limestone b.), alluvial and culluvial with hydromull to mostly active mull humus types. In west of Gilan province, ash forms the association of Fraxino - Buxetum in plain and Fraxino - Aceretum in sub - alpine areas (to border of Rusco - Fagetum). It appears as Fraxino - Alnetum in wet plains of Mazandaran, and as Fraxino - Carpinetum in alluvial plains as well as in cool and humid valleys of Golestan Mountains. it is also found as: - Fraxino – Ouercetum castaneifoliae in upper limit of the Mediterranean vegetation region within valleys of the Alborz mountains. - Fraxino – Ouercetum atropatanae in highlands (upper limit of the Caspian Forests); -Fraxino - Tilietum at connection part of three climate types: Middle Asia, center plateau of Iran and eastern part of the Caspian Sea.Generally, ash dominant association is not estabished in forest types of Fagus orientalis, Quercus castaneifolia - Carpinus betulus and Parrotia persica, except on cool valleys with moist, rich and drained soils, creating mixed stands with other high demanding broadleaved species.