ern edge of its range. In addition, prolonged droughts may also be 

 effective in reducing or eliminating populations of certain peren- 

 nial plants. 



In general, winds in California are relatively unimportant in 

 their influence on plant life, but in many coastal areas the persis- 

 tent and occasionally very strong winds may have an effect in 

 influencing the growth patterns of woody plants. For example, 

 at Point Reyes, Marin County, just north of San Francisco, winds 

 in excess of 75 miles (120 km) per hour are recorded regularly 

 during each month from January through May. Although there 

 are few trees on the coastward portions of Point Reyes, the trim- 

 ming effect can be seen in the pine and bay forests that occupy 

 the exposed ridges just inland from the coast. In southern Cali- 

 fornia, the occasional dry, gusty "Santa Ana" winds may blow 

 toward the coastal regions from the north or northeast. Likewise, 

 in the Sacramento Valley, there are periods during which the dry 

 "Northers" blow. If these strong winds occur during the growing 

 season, they may contribute to a rapid drying of the soil which 

 in turn results in a rather poor growth of native annuals. If these 

 winds occur during the summer months, they considerably in- 

 crease the danger of grass, brush, or forest fires and also aid in 

 spreading fires once they become started. 



At one time in the geological history of CaHfornia the state 

 had a mild, wet climate with abundant rainfall distributed 

 throughout the year. Since Pliocene times, however, the summer 

 season has become longer, warmer, and drier. Total rainfall has 

 decreased and has become Hmited to the winter months. This 

 increasing aridity over a long period of time resulted in striking 

 vegetational changes in the state and was associated with the 

 rather rapid evolution of a large number of plant species that 

 are adapted to the modern climate of the state. At the same time 

 that these species were evolving, a number of plant species and 

 entire plant communities became extinct in the state. 



About half of the plant communities present in California are 

 strongly characteristic of the state and are closely adapted to its 

 present Mediterranean climate. Some of these plant communities 

 are restricted to CaHfornia, or extend only slightly into adjacent 

 areas. Other plant communities are adapted to wetter conditions 



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