But trees may produce plenty of seed and yet fail to maintain their proper proportion in the forest.

This results because much of the seed is unsound.

Even where a satisfactory supply of sound fertile seed is produced, it does not follow that the trees of that variety will be maintained in the forest, as the seed supply may be scattered in unfavorable positions for germination.

Millions of little seedlings, however, start to grow in the forest each year, but only a small number survive and become large trees.

This is because so many of the seedlings are destroyed by forest fires, cattle and sheep grazing, unfavorable soil and weather conditions, and many other causes.
Beech and chestnut trees and others of the broad-leaved type reproduce by means of sprouts as well as by seed.