ternative is to remember that plant communities are defined by 

 man, not by nature, and plants seldom follow the rather rigid 

 limitations set down by man. The variety in the plant cover of 

 California is a reflection of the richness of the flora of the state 

 and of the remarkable diversity of ecological conditions that 

 interact to influence the patterns of distribution of each plant 

 species. 



Succession 



Most of the plant communities that occur in California rep- 

 resent climax plant communities. The idea of climax goes back 

 to Frederick Clements, an American ecologist who invented the 

 term because of its similarity to the word climate. As a mid- 

 westerner it was probably natural that Clements believed that 

 climate was the chief determining influence in the stable vegeta- 

 tion that occurs in any area, but in California other influences 

 (such as soil type) may be extremely important in influencing 

 the distribution of plants. A climax plant community is the final, 

 self-perpetuating plant community that will occur in an area 

 under stable ecological conditions. Examples of climax plant 

 communities in California are Valley and Foothill Woodland, 

 Creosote Bush Scrub, and Valley Grassland. 



However, whenever a plant community is severely disturbed by 

 fire, glaciation, or other ecological influences, it may not be re- 

 placed immediately by re-estabUshment of the same plant species 

 that were present before the disturbance. For example, the first 

 plants to occupy an area in California after a hot forest fire are 

 generally not seedlings of the tree, shrub, or herbaceous species 

 that previously occupied the site, but are seedlings of other 

 species that typically occur after fires sweep through an area. In 

 the upper-middle Montane Forest of the western slope of the 

 Sierra Nevada, there is a characteristic forest flora which is sub- 

 ject to frequent burning. After the fires sweep through these 

 forests, the first plants to appear in the following year are various 

 herbaceous annuals and perennials. Later, shrubs become estab- 

 lished and eventually provide the shade that is necessary for the 

 establishment of seedlings of the climax forest trees (Plate 12B). 

 Seedlings of pines and firs become established under these shrubs 



71 



