Classification of Vegetation Associations from the Mount Tamalpais Watershed, Nicasio Reservoir, and Soulajule Reservoir in Marin County, California

Evens, Julie; Kentner, Ed; Klein, Janet

The Vegetation Program of the California Native Plant Society (CNPS) has worked collaboratively with the Marin Municipal Water District (MMWD) and Aerial Information Systems (AIS) to produce a fine-scale vegetation classification and map on MMWD lands. At least 55 different plant communities, described floristically at the alliance level of the National Vegetation Classification (Grossman et al. 1998), are discussed in this report. Two main project goals are 1) to provide detailed, floristic classification of the vegetation with a report defining the different vegetation types, 2) to provide a detailed vegetation map of the region. Field data are being collected using standard CNPS protocols (e.g., Vegetation Rapid Assessment and Relevé protocols). The field-based classification depicts vegetation types that were sampled in 419 CNPS Vegetation Rapid Assessments and Relevés by MMWD staff. The classification has been produced by CNPS using the National Vegetation Classification System’s hierarchy of alliances and associations. These are floristically and environmentally defined plant communities, such as those described in the CNPS publication of A Manual of California Vegetation (Sawyer and Keeler Wolf 1995). In this project, the vegetation types are depicted in standard descriptions and a field key to concisely differentiate 59 alliances and habitats, of which 88 associations are determined. With these and other data, aerial photography is being analyzed to create a vegetation map by AIS at a fine-scale resolution (with minimum mapping units of 1-2.2 acres). The map is being created by interpreting detailed, digital color aerial photography and delineating boundaries around the individual stands of vegetation in the study area. This detailed map is being produced in 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 plot sampling and reconnaissance points. The final map will include digitization of polygons and attribution of the vegetation type, overstory cover, and tree size. This report mainly represents the results of the vegetation classification from the field sampling effort. This approach allows for baseline information on floristics, vegetation structure, site environment and impacts to be represented in a consistent and accurate manner. As each vegetation type is mapped with the field reference data, the vegetation types can be represented and compared quantitatively. By representing vegetation in this manner, the MMWD is better equipped to manage the vegetation for longterm ecological sustenance. In the future, agencies can compare areas based on vegetation diversity and habitat quality to identify best management regimes for such things as fire hazards, proper trail/road placement, restoration, and other management considerations.