Plant succession and life-zoning are two striking phenomena at Crater Lake. The former is the transition of plant life in a given location from the simplest forms that appear first to the final, complex flora, or climax vegetation. Theoretically, the process of succession follows a definite pattern, with a sequence from lower to higher types of life as the area changes. It is noteworthy that nature often skips some steps as she clothes a mountain.

The park is an excellent place to observe succession of plant types because of the variation of soil conditions from bare rock to relatively great fertility. The process of replacement from the predominance of simple to higher plants is essentially one of breaking the rock down into ever finer particles and enriching it with organic matter so that the latter can exist. This process usually begins with lichens, which come in various colors, ranging from black thru green, yellow, orange, to red. The green, stringy staghorn lichen and the woolly squaw-hair, frequently miscalled mosses, are common varieties of tree lichens. The unusual feature of lichens is that they are actually two plants, an alga and a fungus, growing together. The fungus forms the main body of the lichen, providing it with protection and anchoring it to the rock or tree. Scattered through it the green algal cells contain chlorophyll and manufacture food for the lichen. Such co-operation between organisms is called symbiosis.

Rock lichens are able to decompose enough rock material by their secretions to gain a foothold. Each of thousands of generations of lichens grow, do their bit to disintegrate the rock, then die and contribute a minute amount of organic material. Finally a sufficient amount of soil collects to support mosses. Patches of moss may be found wedged in a protected rocky niche on top of a layer of soil three or four inches thick.

Rock garden plants then take their turn. One of the pioneers is Jacob's ladder, which has small blue flowers with rows of opposite leaves that suggest the rungs of a ladder. These usually occur in the same sites as the patches of moss, as if they had merely exchanged places. Another plant that loves rocky chinks is the western windflower, conspicuous for its white, petal-like sepals and cluster of many stamens and pistils. This blooms in the park in early July. Indian paintbrush, familiar to many, takes its place on the rocky cliffs with its pale orange to reddish bracts that look like a brush dipped into red paint. Also appear the rock loving penstemons, which have red or purplish funnel-shaped flowers.

Normally these wild flowers are followed by woody herbs, the more common and conspicuous of which are the serviceberry, red elderberry, and mountain ash. The flowers of all three are white, but are arranged quite differently. The serviceberry has solitary flowers, subtended by a leaf, and the plant has simple leaves. Both the ash and elderberry flowers are in heads which can easily be distinguished from each other. The flower clusters of the mountain ash are divided into sub-clusters in which the outer have the longer stalks and are attached farther down the stem. This arrangement is technically known as a panicle. Both shrubs have pinnately compound leaves. The climax plants in most areas of the park are evergreens, the type differing with life zones.

The actual process of succession may have omissions and substitutions. On the pumice flats, for example, apparently the lichen and moss stages are omitted; organic material and soil may be brought in by wind and water. As the pumice itself is reduced by weathering certain plants appear without the orderly succession as related above. Soil building is sometimes followed directly by whitebark pines. In another situation, such as a damp area near a stream, ferns, sedges, and grasses may be inserted between the moss and wildflower stages.

Plant succession can also be observed in forest areas that have been burned. On such areas hardy shrubs must enrich the soil before it can again support the plant life that was destroyed. Thus, in the plant successions at Crater Lake, we may see how soil is formed, the evolution of plant cover, and the ways of primitive vegetation on this once rocky earth of ours.