Modern pollen and vegetation relationships in the mountains of southern California, USA

The relationship between modern pollen assemblages and modern vegetation along two elevational transects within the Transverse and Peninsular Ranges of southern California, USA, is demonstrated using cluster analysis of the pollen data. Cluster analysis separates the Sonora Desert vegetation, Valley grassland/agricultural land and chaparral vegetation types on the San Jacinto Mountains transect. Chaparral is not easily separated on the San Bernardino Mountains transect, probably due to the presence of Quercus dumosa (scrub oak) there. The lower montane Quercus - Pinus (oak - pine) community is distinct from other forest types, and can be subdivided palynologically based upon relative importance of Quercus , Pinus and Cupressaceae [primarily Calocedrus decurrens (incense cedar)] pollen. Subdivisions include Quercus - Pinus - Cupressaceae, Quercus - Cupressaceae - Pinus and Quercus - Pinus assemblages. Higher elevation Pinus - Abies (pine - fir) and Pinus -dominated communities are also differentiated from one another, although the subalpine vegetation type only occurs on the San Bernardino Mountains transect. Though the study area presently straddles a transition between winter-wet and summer-wet climatic regimes, differences between the pollen assemblages in the two mountain ranges are minimal. Pollen assemblages from lower elevations document the effects of human activities, primarily agriculture, on the modern pollen rain of the region, with the occurrence of introduced citrus ( Citrus sp.) and shade ( Eucalyptus sp.) trees and weedy disturbance indicators (e.g., Brassicaceae).