48 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



not be long before all the gravity water will have been removed from 

 the upper meter of depth, so that this cause will no longer be oper- 

 ative. The second cause, evaporation directly from the soil, and 

 the third, removal by plants, will continue throughout the dry 

 season. Evaporation from the soil is undoubtedly higher in the 

 chaparral habitat than in the forest, and yet the gradient of depletion, 

 as shown by the graph, is decidedly steeper in the latter. This 

 seems to show that the most potent cause of water-content depletion 



ZW2 



Oft: 

 < *- 



K hi I 



1913 



SEPT. OCT. NOV. 



12 19 26 3 '0 17 24 31 7 14. 22 



1914 

 SEPT. 

 17 24- I 



OCT. NOV. 



8 15 22 30 5 12 20 



oq: 



rid 





20 

 I 5 

 I 

 .5 



U .0 

 19 

 18 

 17 



SE'6 



2,5 

 UJ 



S l4 



>- 13 

 DC 

 O 12 



o" 



I- 10 



z 



Fig. 9. — Soil moisture at end of dry and 

 beginning of wet season, fall of 1913. 

 Jasper Ridge. Wilting coefficients as 

 in fig. 8. 



Fig. 10. — Soil moisture at end of dry 

 and beginning of wet season, fall 

 of 1914. Jasper Ridge. Wilting 

 coefficients as in fig. 8. 



is the vegetation itself, since where the plants are largest and most 

 abundant, there will be the greatest drain upon the water-supply, 

 which statement exactly fits the forest in this case. Measurements 

 given in another connection (p. 112) show that the rate of transpira- 

 tion in the same species growing in both habitats is much higher in 

 the chaparral habitat (in the case of Adenostoma, forest : chap- 

 arral : : 1 : 1.92; in the case of Arctostaphylos, 1 : 1.69). However, 

 it is reasonable to assume that the far greater bulk of transpiring 

 vegetation in the forest, comprising trees of large size and luxuriant 



