REDWOODS, RAINFALL AND FOG 187 



streams becomes very dry, in relatively mesophytie as well as 

 in xerophytic habitats. I have demonstrated this in unpublished 

 work dealing with the ecology of the chaparral. Soil moisture 

 determinations made in the eastern foothill region on opposite 

 north and south facing slopes dominated respectively by chapar- 

 ral (xerophytic) and oak forest (mesophytie) show that the 

 water contents of the two habitats, differing greatly during the 

 rainy season, become almost equally deficient by the end of the 

 dry, 1.4% being the minimum for the chaparral and 3% for 

 the oak forest (average of three depths). The redwood soil in 

 the mountains would doubtless show the same severe depletion, 

 though probably to a somewhat less degree. The evaporation 

 rate too is very high at the critical period. In the week ending 

 September 19, 1913, at the same foothill station, it reached the 

 maximum for the year of 51 cc. loss per day from the porous 

 cup atmometer. 



The redwood is unusually sensitive to the danger of rapid 

 water loss, even when the soil water supply is ample. -This is 

 shown by the following instance. Early in May, 1915, a terrific 

 north wind swept over central California, so desiccating in its 

 effects that roses were turned to paper and gardens showed the 

 effects for weeks afterward. A few days later I crossed the Santa 

 Cruz Mountains and found on the north facing slopes every 

 redwood brown as if scorched by fire. Trees growing in ravines 

 but projecting abo^^e the ridge top were green below and brown 

 above. Frequently trees of redwood and douglas fir were seen 

 side by side, equally exposed. Invariably the redwood was 

 brown and the douglas fir unharmed. In this connection it is 

 of interest to note that in the mountain areas where redwood 

 is practically absent, douglas fir is abundant. 



It is thus sho^ATi conclusively that even in certain mountain 

 areas which have ample winter precipitation, redwood is ex- 

 cluded from all places except the immediate vicinity of streams 

 because of desiccation of the soil during the rainless season 

 accompanied by high evaporation rate. This state of affairs 

 might be improved by the lowering of the evaporation rate, 

 resulting in conservation of the hmited supply of available 



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