Sequoiadendron giganteum, the largest living thing on Earth, begins life looking very much like a blade of grass. If conditions are just right, the seed first becomes slightly swollen and then cracks open as the radicle, or root, reaches out and then downward into the soil. If the seed is slightly buried, the bright green hypocotyl, or stem, presses upward through the soil bent over double - an upside-down "U" shape - with the middle of its delicate little stem leading the way. Very often, as the sprout begins to straighten up, the seed coat is carried along with it up into the air. After a few days, however, the empty shell of the seed pops off, and then for the first time the little giant sequoia stands upright - a full inch tall.
Already the seedling is one of an extremely small minority since even germination is rare under ordinary natural conditions. Only a tiny fraction of one percent of sequoia seeds ever germinate.
In addition to genetic factors, the germination of sequoia seeds depends on a strict balance of interrelated environmental factors. Ten to twenty days of full sunlight, for instance, will kill the seed embryo even before it can begin to germinate. Soil moisture levels between five and sixteen percent are optimal. Soil temperature is also a crucial factor during germination. Giant sequoia reproduction is likely to be hindered at either the upper or lower elevation limits of the range by adverse combinations of temperature and moisture.
The availability of exposed mineral soil is another extremely important environmental factor in giant sequoia germination. Studies have shown that giant sequoia seeds must germinate within a half-inch of the soil surface in order for the seedlings to become established. Because of these rather narrow limits, the relationship of the seed to moist mineral soil is a major factor in giant sequoia regeneration.
Excerpted from "The Enduring Giants" by Joseph H. Engbeck Jr., published by the California State Parks.