Every plant on Earth occurs in a certain region that can be marked out on a map. This region is termed its area of natural distribution. Knowledge of these areas is of great importance, because the woody plant grows for hundreds, and even thousands, of years in the given area, and is adapted to the climatic conditions of the locality, thus making it possible to determine whether it prefers a coastal or inland, lowland or alpine climate. The study of other data reveals what temperatures it is able to withstand in winter, as well as its soil and moisture requirements.

The white ash reaches a height of 30 to 40 metres and the bark is more coarsely furrowed than that of the common ash. It also differs from the latter in having brown buds. The odd-pinnate leaves are composed of broader, ovate leaflets and the seeds are narrowly lanceolate, about one-half narrower than the tongue-shaped wings. The seed, unlike that of the common ash, germinates in the spring of the following year. As it grows no faster than the common ash and its wood is of poorer quality it is not cultivated in European forests, though it has some value as an ornamental specimen tree in parks and avenues, especially on the poorer soils.

The manna ash is a tree of south-eastern Europe, where it grows south of the Alps and Carpathians. It occurs in Spain and southern France, but the chief centre of its distribution is Italy and the Balkan Peninsula, where it is found on dry, sun- warmed slopes in oak forests. In the northern areas of its range, it occurs chiefly on limestone soils. In the mountains it may be found at elevations up to 1200 metres.

Pines from the lower, dry elevations of central Europe, on the other hand, have broad crowns to shade their site as much as possible. Similarly, mountain spruces growing at high elevations, or in cold valleys, have slender, narrow crowns.

The manna ash thrives on well-drained soils that are exposed to strong sunlight in the summer. It is, however, tolerant of soil conditions and will grow in cooler climates. It is an important tree in the afforestation of karst areas and dry slopes devastated by grazing. In former times, the liquid “manna” (sap) yielded by the bark was used for pharmaceutical purposes in Italy.

The boundaries of the area of natural distribution, however, do not constitute a line of demarcation outside which plants would not prosper.