these have become sorted out from the Chaparral and occur in 

 another plant community to the south. 



Uplift of the mountain ranges had an important effect in cre- 

 ating new habitats because of the cooler climates that prevail in 

 upland areas and because of the increased rain- or snowfall on 

 the western slopes of the mountains. The Montane Forest and the 

 Subalpine Forest plant communities both occupy habitats that 

 were not present before the upHft of the mountains in the Plio- 

 cene. However, most of the genera of trees present in both of 

 these plant communities were also present in the Miocene Arcto- 

 Tertiary geoflora and are likely derived from these species. The 

 plant species present in the Alpine Fell-field plant community 

 were not derived from precursors present in the forest communi- 

 ties. Some of these species undoubtedly migrated into their pre- 

 sent habitats from similar habitats far to the north. As a conse- 

 quence, some species in these fell-fields are related to those pre- 

 sently widespread in arctic regions. A second source of derivation 

 of these high altitude plants is from the adjacent deserts; some 

 of the genera of the fell-fields (such as Eriogonum) fall into this 

 category. It is not surprising that this desert derivation has oc- 

 curred, since the fell-field climate is virtually that of a desert, 

 albeit one at a very high altitude. 



The three geofloras that have been discussed were complexes 

 of several distinctive plant communities, and their composition 

 and ranges fluctuated considerably over long periods of geo- 

 logical time. On the average, however, the two geofloras that 

 have made major contributions to the contemporary flora of Cal- 

 ifornia were very different ones, adapted to different average 

 climatic regimes. As a consequence, the plant communities de- 

 rived from these two geofloras have sorted themselves out into 

 a fairly well-marked pattern: the Arcto-Tertiary derivatives cur- 

 rently inhabit the mountainous areas and the northern part of 

 the state, both of which are comparatively cool and well-watered; 

 the Madro-Tertiary derivatives occupy the cismontane and the 

 southern portion of the state including the deserts. Although 

 there is seemingly little direct heritage of the Neotropical Ter- 

 tiary geoflora in contemporary California, it is likely that some of 

 the California representatives of essentially tropical families may 



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