Also, because of the prolonged summer drought in much of the 

 state, plants that are unable to survive long periods without rain- 

 fall do not become estabhshed. In general, winter rains are more 

 or less dependable, but there are some notable exceptions to this 

 reliability. For example, in the winter of 1850-51 San Francisco 

 received only slightly over 7 inches (18 cm) of rain, which is 

 about one-fourth of its average rainfall. Clearly, that year was a 

 "bad" one for the plants! Also, prolonged drought during the 

 winter may also exert a negative influence on plants, even though 

 early winter and late winter rains may produce an average total 

 amount of rain for the year. It is these seasonal or yearly bottle- 

 necks in rainfall that have a very important local effect on plants. 



As mentioned above, the rain in CaUfornia tends to be highly 

 seasonal and the summers are generally very dry and rainless. In 

 northern CaHfornia, the occurrence of heavy fogs along the coast 

 has a two-fold beneficial effect in alleviating some of the effects 

 of summer drought. One of these effects is that the fogs reduce 

 the amount of water loss from plants and from the soil so that 

 wiiat little water there is can be conserved. A second effect is 

 seen in the familiar "fog drip" that occurs from the foliage and 

 branches of tall trees along the coast. This is particularly notice- 

 able in redwood forests, but also occurs in other coniferous 

 forests, as well as in eucalyptus groves in some areas. The fog 

 that condenses on the upper portions of the trees drips down to 

 the soil and in some areas has been estimated to be equivalent to 

 an extra ten inches of rainfall per year. 



Snow is also important as a source of moisture for plants and 

 serves as an important insulating agent for many plants in alpine 

 areas that have severe cold and strong winter winds. Snowfall in 

 the winter can be expected in the Sierra Nevada at any elevation 

 above 2,000 feet (610 m). Above 4,000 feet (1,220 m) the snow 

 may remain on the ground for long periods of time, and at 

 higher elevations snow remains on the ground during the entire 

 winter. The coastal region is mostly free of winter snow, althou^ 

 peaks in the Coast Ranges and the southern California ranges may 

 have snow on the ground for days or weeks at a time. The snow 

 season in the Sierra is between October and June, the actual 

 length of time depending on the season and on the elevation. 



41 



