22 THE BROAD-SCLEROPHYLL VEGETATION OF CALIFORNIA. 



Pasania-Quercus- Arbutus Association. — This community is charac- 

 teristic of the lower altitudes of the North Coast Ranges, a region 

 very complex and rather difficult to understand vegetationally, 

 since two or more types which are climactic nearby meet here and 

 overlap, finding conditions that are reasonably favorable to all. 

 The redwoods thoroughly dominate the coast. East of them 

 Pseudotsuga mucronata is the commanding species, but shares its 

 rule with the broad-sclerophyll association about to be described. 

 Chaparral and grassland communities also occur, but these are 

 plainly successional. The Pasania-Quercus- Arbutus association is 

 itself somewhat of a transitional unit between broad-sclerophyll 

 and conifer types, for it rarely occurs without at least a sprinkling of 

 conifers, especially Pseudotsuga, and its principal species occur 

 commonly as an understory of the Pseudotsuga and Sequoia forests. 



The most important species of the formation are Pasania densiflora, 

 Quercus chrysolepis, and Arbutus menziesii, and these attain great 

 size. Other tree species occurring more or less commonly are 

 Quercus kelloggii, Castanopsis chrysophylla, Umbellularia californica, 

 Acer macrophyllum, JZsculus californica, and Cornus nuttallii. The 

 association ordinarily possesses two layer societies — one of shrubs, 

 including Corylus rostrata californica, Vaccinium ovatum, and Gaul- 

 theria shallon, and one of herbs and ground-shrubs, a mixture of 

 typically oak-forest species and those commonly associated with the 

 redwood and douglas fir. 



The transitional phases of the association will be made evident 

 by description of two areas, one in the interior of the Coast Ranges, 

 where Pseudotsuga is the competing tree, the other on the edge of 

 the coastal redwood region. 



The first locality is in Trinity County, on the north-facing slope 

 of the Mad-Trinity Divide. The dominant tree, Pseudotsuga, grows 

 here magnificently, many specimens attaining a diameter of 2 

 meters. Abies concolor and Pinus lambertiana also occur. Beneath 

 the conifers there is an understory of broadleaf trees, nearly all 

 sclerophylls. Castanopsis chrysophylla is the most abundant, and 

 Pasania, Arbutus, and Acer macrophyllum also occur. This assem- 

 blage might here be termed a layer society. Corylus rostrata cali- 

 fornica, Cornus nuttallii, and Ceanothus integerrimus form a second 

 stratum, and a third is composed of herbs and ground shrubs: 

 Vancouveria sp., Polystichum muniturn, Berberis sp., Gaultheria 

 shallon. 



The other is the valley of the South Fork of the Eel River, in 

 Humboldt County. In the vicinity of Garbersville and for several 

 kilometers north of it (downstream), the north slopes and ravines 

 are forested with Pasania densiflora, Quercus kelloggii, Q. chrysolepis, 

 Q. garryana, Arbutus menziesii, Umbellularia californica, Msculus 



