Vegetation alliances of the San Dieguito River Park - California ...

INTRODUCTIONThe Vegetation Program of the California Native Plant Society (CNPS) has workedcollaboratively with local and regional agencies, including the California Department of Fish andGame (CDFG), in producing a vegetation classification and map of the San Dieguito River Park.The San Dieguito River Park occurs in San Diego County, California, and extends 55 miles fromSan Dieguito Lagoon at Del Mar to its headwaters in the Peninsular Range at Volcan Mountain.At least 86 different plant communities, described floristically at the alliance level of the NationalVegetation Classification (Grossman et al. 1998), are discussed in this report.Two main project goals are 1) to provide detailed, floristic classification of the vegetationand a report defining the different vegetation types, 2) to provide a detailed vegetation map of theregion. Field data are being collected using standard CNPS and CDFG protocols (e.g.,vegetation rapid assessment protocol), and these data and color imagery are being analyzed tocreate the classification and maps.The field-based classification depicts vegetation types that were sampled and identified in579 vegetation rapid assessments. The classification follows the National VegetationClassification System’s hierarchy of alliances and associations. These are floristically andenvironmentally defined plant communities, such as those described in the CNPS publication of AManual of California Vegetation (Sawyer and Keeler Wolf 1995). In this project, the vegetationtypes are depicted in standard descriptions and a field key to concisely differentiate 86 alliances,2 unique stands, and 103 associations.In a parallel effort, the alliance and association-level classification is being used to createa vegetation map at a fine-scale resolution (minimum mapping unit of 1/2-1 acre). The map isbeing created by interpreting detailed, digital color aerial photography and delineating boundariesaround the individual stands of vegetation in the study area. This detailed map is being producedin a Geographic Information System (GIS) digital format, through a “head’s-up” digitizing process.With the field data collected and classified, the mapping is guided by the 579 rapid assessmentsand 595 reconnaissance points. The final map will include digitization of polygons and attributionof the vegetation type, tree cover, shrub cover, herb cover, tree size, site quality and impacts.Over the past 15 years, there has been a proliferation of Habitat Conservation Plans(HCP) and Natural Communities Conservation Planning programs in southern California;however, these projects suffer from a lack of sufficient field vegetation information. Presently,only coarse-scale vegetation maps exist from the San Diego County Multiple SpeciesConservation Planning area, in which the vegetation is not precisely defined or mapped. Thus,collection of detailed field data for floristic vegetation classification and mapping will assist inmore appropriate conservation and management decisions to sustain California’s natural andunique resources. The San Dieguito vegetation descriptions and map will be shared with localand regional organizations and agencies for land management and conservation purposes.This is the first time a collaborative vegetation project has provided detailed vegetationand site quality information over the range of biodiversity in this portion of California, from theinterior mountain drainage to the coastal lagoon of the San Dieguito. With a fine-scale vegetationclassification and map, we can be more certain that the full range of ecological variability iscaptured in the San Dieguito River Park. As each vegetation type is mapped, it has referenceground data so that the vegetation types can be compared quantitatively. In the maps, baselinefloristic, structural, and site impact information is captured in a defensible manner. Once we havea map of scientifically and quantitatively based units, we can determine location, acreage,numbers and quality of vegetation types. Ensuring representation of each vegetation type willassist in ecological sustenance of the region. In the future, agencies can compare areas basedon vegetation diversity and habitat quality to identify conservation values for such things as landacquisition, proper placement of trail systems, restoration, and other management in the RiverPark.CNPS is currently collaborating with a variety of local and state agencies in this project,many of whom own/manage land in the River Park. The CDFG-Wildlife and Data HabitatAnalysis Branch and the San Diego Chapter of CNPS have been instrumental in providing work1