The Centers of Distribution of the Chaparral and Coastal Sage Associations

Abstract

The vegetation of cismontane Southern California consists chiefly of three well defined communities of different aspect and habit: the oak woodland, the chaparral and coastal sage associations. The first of these, as its name implies, is a woodland whose principal component is Quercus agrifolia, with which are variously associated such species as Q. Engelmanii and Juglans californica. This woodland is for the most part poorly developed in Southern California, where it appears to be relictual, chiefly occupying small valleys and potreros, on moister hillsides. It is surrounded and in many places all but engulfed, by the chaparral and coastal sage. It reaches its typical development in West Central California and may be interpreted there as a coastal expression of the oak woodland of the Great Valley. It extends southward as far as Santo Tomas in Baja California. We are concerned only indirectly with it here. The chaparral and coastal sage communities are the characteristic and widespread associations of the area under discussion. They are not confined to Southern California, however. The former ranges in typical form into the North Coast ranges, being widely developed in Lake County and in corresponding latitudes in the Sierran foothills. It reappears in Central Arizona into which region at least three California species extend, and again, according to M?ller (1939, and personal communication) in Chihuahua, Coahuila, and Nuevo Leon. Its aspect there is strongly suggestive of California chaparral, as described by Cooper. Although several generic representatives are found common to both areas, such as Quercus, Ceanothus, Cerocarpus, Rhus, Arctostaphylos, and Garrya, the species differ, with the chief exception, perhaps, of Arctostaphylos pungens. Whether that species is actually common both to Nuevo Leon and to Southern California may be open to question. In any case, closely related phylads are represented, not only by Arctostaphylos, but also probably by Cercocarpus, Garrya, and Ceanothus. The scrub oaks of the Nuevo Leon association are not of the Quercus dumosa phylad, however, but are predominantly semi-deciduous oaks of Mexican alliance. According to M?ller, it would appear that, although it has much the same aspect and habit, the chaparral of Nuevo Leon and Coahuila is a more diversified community than the chaparral of California, that is, harbors more elements which in California are found in other associations, as for example, Agave, Nolina, juniperus, Pinus cembroides, Mahonia Fremontii, and Arbutus. In Nuevo Leon some of these elements, for example, Pinus, Juniperus and Arbutus, are not restricted to the chaparral, but occur freely and in true form in the adjacent forest types. As one proceeds westward, according to M?ller, the 445