130 F. E. Clements 



response to climatic pulsations and, as at present, it must have 

 been the chief resource of the ungulates during periods of 

 drouth. 



The chaparral climax, representative of the next zone above 

 with higher rainfall, naturally suffered more from the trend 

 toward desiccation and the number of transads is correspond- 

 ingly smaller. However, almost all the important genera except 

 Adenostoma and Heteromeles are represented, mosdy by species 

 transads or by phylads that cross the desert, as in the case of 

 Querciis dumosa, Prtinus demissa, Aesculus californica, and Cer- 

 cis occidentalis. Furthermore, an additional genus, Garrya, is 

 ^ found in the Pleistocene at Rancho La Brea; another, Robinia, 

 in the Pliocene of the Ricardo; and a large number of the actual 

 species occur in one or both of these horizons elsewhere in Cali- 

 fornia. On the basis of phylogeny and association, chaparral must 

 have been in existence in its proper position in the clisere of the 

 Miocene or earlier, but it undoubtedly received recruits from 

 time to time as the climate became drier. Although some of its 

 dominants were undoubtedly utilized by browsers and the nuts 

 and berries by rodents and birds, this community must have 

 played a smaller part in the general economy. 



In the existing vegetation, woodland takes a m^inor role as a 

 climax, though in the reduced form of savannah it covers a wide 

 area from the Edwards Plateau of Texas to the Coast Ranges and 

 north into Oregon. Its major components are junipers, nut pines, 

 and live oaks, though it may contain other pines and evergreens 

 such as Pinus sabiniana, Umbellidaria, or Arbutus, or, more 

 rarely, such deciduous trees as Quercus douglasi and Aesculus 

 californica. Probably the Joshua tree. Yucca brevifolia, finds its 

 most natural position here also. As species with varieties, both 

 Pinus and Junipei'us were present, as was Cufn-essus; the evi- 



