from the Introduction
California is a land of superlatives. It has the highest mountain peaks, the largest, oldest and tallest trees, the rivers of the greatest variety, and the most diverse Indian tribes found in the coterminous United States. California arbors the smallest bird on the continent north of Mexico, the calliope hummingbird (Stella calliope), and the largest bird, the California condor (Gymnogyps californianus). From the summit of Telescope Peak in the Panamint Range, one can face east to see the lowest point on the American continent, in Death Valley, and then turn around to gaze at the highest point of land in the United States outside Alaska, the summit of Mount Whitney, 14,501 feet above sea level.
Not unlike that of an isolated island, the plants, animals, landscapes and native peoples of California have a distinctness and unusual diversity that casts them apart from the rest of the mainland. This is apparent to every European visitor during the period of early exploration. One-third of the state's 6300 native plant species are endemics and grow nowhere else on earth. It has nineteen of the ninety oak (Quercus) species that grow in the United States. And it contains nearly all the world's approximately sixty species of manzanitas (Arctostaphylos spp.) and three-forths of the forty-five species of California-lilacs (Ceanothus spp).
In 1542 one hundred languages resonated across California's myriad landscapes - one quarter of the 418 native languages that existed within the borders of the present-day United States. Alfred Kroeber, the father of California anthropology, split the state into six major Native American culture areas, which reflect the state's tremendous variety of lifestyles. The archeologist Michael Moratto states, "Such cultural, linguistic, and biological variations bespeak a long and rich prehistory in this part of the Far West."
California poppies set a tilted mesa north of Pasadena aglow with their blooms in spring, serving as a beacon to ships more than twenty-five miles away. Seeing hillsides covered with these flowers, early Spanish explorers named the coast "the Land of Fire," appropriate in a literal as well as a figurative sense because of the hot, arid summers and the frequency of fires ignited by lightning strikes.
The Role of Natural Disturbance
According to the plant ecologist Michael Barbour, "Late summer and early fall fires were an expected natural event in many California vegetation types below six thousand feet elevation. The same acre of ground could be expected to burn every ten to fifty years. Fire was uncommon only in deserts at high elevations. California plants evolved with fire as a natural environmental factor over millions of years. As a result, not only do many California species survive fires, but some require fire in order to complete their life cycle or to remain vigorous" The ecologist Richard Vogl has postulated that fire helped to shape three-fourths of California's vegetation.
Fire was not the only occurrence shaping the landscape. Spring floods scoured watercourses and deposited silt, small and large mammals dug in the soil, storms felled trees, and torrential rains caused landslides. Each of these common events is known by plant ecologists as a natural disturbance, defined as 'any relatively discrete event in time that disrupts ecosystem, community, or population structures and changes resources, substrate availability, or the physical environment." Having evolved with these erratic or episodic perturbations, many plant species not only tolerate them, but require them to complete their life cycles or to maintain dominance.
Ecological studies from all over the world, in both aquatic and terrestrial ecosystems, bear out the ecological role of disturbance in the development and maintenance of forest, shrubland, grassland, and wetland habitats. In many instances, moderate to medium disturbance promotes habitat heterogeneity and allows for greater diversity of plants and animals. For example, small mammal activity increases the abundance and diversity of geophytes (Perennials with bulbs, corms, or tubers); wave action contributes to biodiversity in the rocky intertidal zone; fires maintain biologically rich grasslands; and the alternate filling and draining of lakes, marshes and estuaries supports vast populations of aquatic life and waterfowl. Some scientists suggest that pyrodiversity (the diversity in frequency, scale, season, and type of fire) leads to great biodiversity of plant species and vegetation types.
Disturbance is a recurrent feature of virtually every vegetation type in California. In fact, it is now accepted that perturbations are -required- for the rejuvenation of many plant populations and ecosystems. According to a hypothesis put forth by the ecologist Joseph Connell, disturbances that occur at intermediate intensities and frequencies promote the greatest biological diversity.
