The quantity of seeds in a good year is enormous. One hectare of forest planted with five to fifteen thousand young seedlings will yield up to three million seeds for a pine stand, five million for spruce, three to five million for beech and up to a hundred million for birch.

Simultaneously, however, there are great losses both of the seeds and the young plants. Large quantities of seeds are eaten by birds and animals and many fall in places unsuitable for growth where they either do not germinate at all or die shortly after germinating, having used up the store of food in the seed. Similarly, many young trees are destroyed in their first years by drought, frost, invading grass or other plants, or by animals that feed on them. Of the huge crop of seeds, all that usually remains within a few years is less than one per cent per hectare.

To ensure that they fall in a suitable open space and do not merely drop beside the parent tree, where the prospects for their further growth are poor, the seeds are adapted for dissemination to longer or shorter distances. Most are equipped for dispersal by the wind and are either covered with down (willow, poplar) or have membranous wings (birch, elm, pine, spruce) or thick wings (maple, lime, hornbeam). The seeds of another group of woody plants are dispersed by animals, mainly birds. In general these are trees with pulpy, bright coloured fruits which serve as food for the birds, the seeds then being disseminated over a wide area in their excrement (mountain ash, cherry, yew).

A closer look at the type of seed, its method of dispersal, and t be biological characteristics of a given tree, will reveal that all are closely linked with an efficiency found over and over again in nature.

True fruits are further divided into dry and fleshy fruits.

Naturally, it would drop to the ground while being carried; and thus the offipring of a given tree might take root several hundred kilometres from the parent. In this way even these trees migrated hundreds of kilometres to the north within Itirly short space of time.