Blue oak communities in California

Twelve blue oak plant communities at the subspecies level of classification are described for California. Community analysis was based on 1000 Vegetation Type Map plots containing information on species composition, number of trees by species and diameter class, and environmental variables including elevation, slope, aspect, and parent material. Community structure is related to environmental variables in order to understand the possible responses of blue oak communities to natural and human-caused disturbance. Blue oak ( Quercus douglasii Hook. & Arn.) (QUDO) woodlands occupy approximately 1.2 million hectares of California (Bolsinger 1988). They are the most extensive hardwood rangeland types, found both in the Coast Range and Sierra Nevada, as well as occupying a fairly well defined ring around the Central Valley (Griffin and Critchfield 1972). The woodlands range from 100 to 1200 meters in elevation and from northern Los Angeles County to the head of the Sacramento Valley in Shasta County (Munz 1973; Griffin and Critchfield 1972). Prominent in the foothill woodlands of the state, blue oak communities form a transitional zone between the valley grassland and the higher elevation mixed coniferous forest. Blue oaks have become the focus of many recent studies because of the increasing awareness of the loss of blue oak habitat from land conversion and fuel wood harvesting (Ewing et al. 1988), and the lack of regeneration on many sites (Muick and Bartolome 1987). Bolsinger (1988) estimates that 7 5 percent of the blue oak woodlands resource is in private ownership, 14 percent in the National Forest Systems, and the remaining in other state, county, and miscellaneous federal ownerships. Existing systems for describing and classifying hardwood rangelands are too general for planning and development of site-specific management practices (Allen et al. 1989). Existing systems also cannot provide accurate enough classification of ecological types to generalize experimental results. Allen et al. (1989) developed an ecologically based classification system for oak woodlands in California. Seven series, based on tree dominants, and 57 subseries were identified. The subseries level of classification was developed from all species present, rather than dominants only. The classification term "association" was not used Madrono, Vol. 38, No. 2, pp. 80-95, 1991 This content downloaded from 207.46. 13.38 on Sat, 21 May 2016 04:54:52 UTC All use subject to http://about.jstor. org/terms 1991] ALLEN-DIAZ & HOLZMAN: BLUE OAK COMMUNITIES 8 1 because all grass species were lumped into one category, thus subseries better reflects the level of detail in classification hierarchy. The system provides researchers, land managers, landowners, and the general public with a better description of the state's oak woodland resource, and unlike previous systems is based on actual plot data. Blue oak woodlands were one of seven oak woodland series identified in the Allen et al. (1989) report. This paper describes blue oak subseries in California. It relates community structure to environmental variables, and suggests subseries appropriate for studying succession and/or management practices in blue oak woodlands. The subseries descriptions should be particularly useful for linking research to management.