Of those few seeds that do germinate naturally in an open forest where conditions are close to ideal, only a very small percentage will survive. Some germinating seeds never come in contact with mineral soil; others may be too deeply buried and therefore fail to obtain sufficient sunlight. Even among those seedlings that are favorably placed and have adequate sunlight and good access to mineral soil, only about ten percent will ordinarily survive the first two summer dry seasons.
Studies have shown that before human intervention and suppression of fire, much of the primeval Sierra forest was open and "park-like." This kind of forest favored the natural regeneration of sequoias instead of the shade tolerant species such as fir and incense cedar. Moreover, occasional fire also favors the germination and temporary spread of certain kinds of chaparral. In fact, some chaparral species - deer brush (Ceanothus integerrimus) and snow brush (Ceanothus cordulatus), for instance - are so closely fire related that their seeds germinate in abundance only with the help of fire.
Instead of becoming permanent in any given location, however, the chaparral community tends to produce conditions that are ideal for the establishment of other plants, shrubs, and trees like the giant sequoia. Giant sequoias have been known to seed into chaparral areas even on some very hot, southwest-facing slopes where, without the chaparral, conditions would have been far too hot and dry for either germination or subsequent survival of sequoia seedlings. After thirty to fifty years, old age begins to overtake a generation of chaparral, and if trees have seeded into the area the shade of the developing forest effectively inhibits chaparral regeneration so that it eventually begins to die out and disappear.
Though fire plays an important role in plant succession and thus in giant sequoia germination and seedling survival, it can also be thoroughly destructive. In the seedling stage, for instance, giant sequoias are extremely vulnerable to fire.
The same general factors that are critical to giant sequoia seed germination continue to be critical to seedling survival though the range of acceptable conditions becomes broader as seedlings become better established. Probably the most limiting factor, however, is the availability of moisture. This can be a serious problem even in the heart of well-established sequoia groves, many of which are located in relatively well-watered flats fed by year-round streams. Outside of established groves the availability of moisture is likely to be an even more severe problem.
Excerpted from "The Enduring Giants" by Joseph H. Engbeck Jr., published by the California State Parks.