24 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



Coast Ranges, being locally of considerable importance in the San 

 Francisco Bay region. The dominant species are Quercus agrifolia 

 and Q. lobata, the latter being deciduous. The trees as a rule stand 

 far apart, producing a park-like landscape, and it is in such places 

 that the largest specimens of both species occur. One tree of 

 Q. agrifolia near Palo Alto is 2.1 meters in diameter breast-high. 

 A specimen of Q. lobata west of Clear Lake is of the same diameter, 

 with a spread of branches of 47 meters. Much larger trees of the 

 latter have been reported. Other species are of occasional occurrence. 

 In the Palo Alto region large specimens of Umbellularia, Arbutus 

 and Prunus ilicifolia make a small part of this association. Because 

 of the wide scattering of the trees, the ground between is in most 

 places under cultivation. Near Palo Alto, however, there are a 

 few localities which retain their original vegetation, because they 

 have long been included in certain large estates. In such areas one 

 finds the two oaks of all sizes from seedlings to large mature trees. 

 Most of the young ones occur in indefinite groups in the opener places, 

 while the mature specimens completely dominate the ground beneath 

 them. Three layer societies occur. The first, of tall shrubs, includes 

 Rhamnus californica, Heteromeles arbutifolia, Sambucus glauca, 

 and Rhus diversiloba. The low-shrub society includes Rubus viti- 

 folius, Symphoricarpos racemosus, and Solanum umbelliferum. Mic- 

 romeria chamissonis is dominant in the ground layer society. Further 

 details concerning this very interesting association will be given in a 

 future paper upon the communities and successions of the Palo 

 Alto region. 



Quercus chrysolepis-kelloggii Association. — The associations so 

 far described are distinctly of low altitudes. The present one belongs 

 to the higher Coast Ranges and southern California mountains and 

 to the middle altitudes of the Sierras. It is preeminently a north- 

 slope forest, but localities are common enough where it occurs on 

 other exposures as well, seeming like a true climax. The most 

 important tree species is the broad-sclerophyll Quercus chrysolepis; 

 Q. kelloggii, deciduous, is often a close second. Others are Arbutus, 

 Umbellularia, Acer macrophyllum, Pasania, ALsculus. Since the 

 association has so great a range, the subordinate vegetation varies 

 greatly. It shows broad transition areas with neighboring associa- 

 tions. Its close relation to the Pasania-Quercus- Arbutus association 

 is at once evident, and it is not strange, therefore, to find areas that 

 can not be placed with certainty in either. Again, just as the 

 Pasania-Quercus-Arbutus association passes into the Sequoia forest 

 as an understory, so also does the Quercus chrysolepis-kelloggii 

 association into the pine forests of the high Coast Ranges and the 

 Sierras. In fact, in the Sierras it is commoner to find the community 

 as an understory beneath Pinus ponderosa and P. lambertiana than 



