Vegetation

Vegetation

The vegetation of the study region is a result of a combination of natural conditions including climate, soil type, soil moisture, elevation, and solar aspect. It is classified by the California Natural Diversity Database/Holland code (hereafter Holland, 1986), a 5-digit numbering system which identifies and groups California plant species into 375 plant communities by majority vegetation type. Although the Holland code descriptions are detailed, it should be noted that they are not complete. For example, Coulter Pine, Pinus coulteri, is not found in the Holland code category for Conifer Trees; however, Coulter Pine is found in the study area and is represented in the California Wildlife Habitat Relation (WHR) model used in the assessment of species richness. The major vegetation groups in the study area are Herbaceous, Chaparral Shrubs, High Desert Shrubs, Desert Shrubs, Coastal Sage Shrubs, Great Basin Shrubs, Hardwood Trees, and Conifer Trees. The distribution of major plant communities in the study region is shown in figure 45.

While vegetation is important as its own entity within a study of biodiversity (see Davis, et al., 1995), it is also essential to understand the relationships between vegetation types and species habitats. The several measures of biodiversity --landscape ecological pattern, single species potential habitat, and species richness-- all depend upon the type and distribution of vegetation.

Vegetation will be altered directly and indirectly in any alternative future. The direct changes are principally those related to the construction of new development. As was seen in the Plans Build-Out change bar chart, figure 16, change may directly impact several natural vegetation groups: riparian vegetation (5,000ha), oak woodland (25,000ha), mixed forest (10,000ha), sage chaparral (300,000ha) and grassland (55,000ha). In addition, considerable amounts of orchard, agriculture, and altered but non-built land will be converted to urban uses.

There are also indirect changes associated with urbanization which may impact vegetation land cover. Among these are increased avocado plantations, changes in riparian vegetation caused by increased flooding, upland vegetation changes caused by decreased soil moisture, changes caused by increased fire frequency, and vegetation changes caused by fire suppression in new developed areas. The areas where the vegetation pattern associated with Plans Build-Out is at risk to change are seen in figure 46.