Trees are divided roughly into three groups according to their rate of growth - fast, moderate and slow-growing.

The first group is distinguished by fast growth in the first years with culmination point at an early age, after which the rate markedly decreases. The tree usually has a short life. Fast-growing trees, therefore, do not attain great heights; on the contrary, these are attained by the moderate and slow-growing over a greater period of time, and reaches its peak at a more advanced age; the downward curve is more protracted and the tree has a longer life span (fir, spruce, beech).

The tallest and largest trees are the sequoias of North America (Sequoiadendron giganteum Buchh. and Sequoia sempervirens Endl.), the latter attaining heights of up to 112 metres or more. Heights of 80 to 90 metres are reached by some other west American conifers, e.g. the giant fir, noble fir, Douglas fir and sugar pine. Of the European trees the tallest is the European silver fir with a height of over 62 metres and the Norway spruce, which also attains a height of over 60 metres.

Conifers generally lack it altogether, and in early youth it is found only in the yew, eastern arbor-vitae and some cypresses. Almost all broad-leaved trees exhibit this ability in youth, but later, after the age of maturity, it disappears in of trees with a constant ability to produce suckers in great abundance includes the willow, poplar, lime, hornbeam, alder, black locust, elm and oak, those with a moderate output include the maple, ash and mountain ash.

If conditions are favourable, the seeds of most woody plants germinate within three to four weeks of sowing. But in some trees the period of germination is longer when sown in spring. If the seeds have become too dry during the winter storage they may not germinate at all, or else not until the following Npring. This is true of many seeds, particularly of large seeds or those that fall from the tree in the autumn (silver fir, Douglas lir, white pine, common yew, oak, beech, chestnut, maple, etc.).

In planting new forests, willows and poplars are grown directly from cuttings, as are most ornamental trees and shrubs. Some trees can also multiply by their pendulous branches touching the soil and sending out roots. Their tips then grow upward, and new individuals are formed. This method is characteristic of the Norway spruce in high mountain areas, the lime growing in stone debris or parks, the arbor-vitae and many ornamental shrubs.