Project Summary

California wines have become extremely popular nationally and internationally, leading to increased demand for wine grapes. Upland areas, historically considered marginal agricultural land, are increasingly targeted for vineyard development. In some areas, the conversion from woodlands and forestland to vineyard is extensive. For example, Santa Barbara County Planning Department reported that the amount of vineyard has doubled to 20,000 acres since 1996 leading to the loss of over 2,000 oak trees, a larger number than all rural development and subdivisions were responsible for removing in the past ten years. Most recently, a 10,000 acre vineyard is being proposed in what is now currently coastal redwood forest lands - the largest single conversion of its kind. Understandably, vineyard owners are coming under increasing scrutiny from urban neighbors, the environmental community, and government agencies concerned about the effect of vineyards on natural resources. For example, riparian vegetation clearing, wetland conversion, endangered species, hillside erosion, native tree removal, and impeded wildlife migration corridors have become contentious issues facing vineyardists in California.

In response to citizens concerns, local regulatory policies are rapidly evolving to prevent hillside erosion and protect natural resources. In particular, Sonoma County recently instigated hillside agricultural development restrictions to prevent soil loss and protect stream corridors. This local ordinance requires farmers to register new vineyards and represents some of the first restrictions to agricultural development in California.

The results from this research project currently provides an assessment of where vineyards are in Sonoma County and addresses the related natural resource issues and local policies that are associated with hillside agricultural expansion. The vineyards mapped in these figures are in the major wine grape growing regions of Sonoma County. Using this data we calculated that approximately 12,000 acres of new vineyards were planted from 1990 through 1997. This makes a total of at least 48,000 acres in 1997, 20% more than were reported in the 1998 County Crop Report. From this data we were also able to measure the extent to which recent vineyard development has moved to steeper hillsides (see chart). In fact, 25% of the vineyards developed since 1990 were on slopes greater than 10 degrees and 42% are above 100 meters in elevation. For comparison, less than 6% of the vineyards established prior to 1990 were on slopes greater than 10 degrees and only 18% were above 100 meters.

In order to evaluate the consequences of proposed and enacted local regulations on agriculture and the environment we mapped the areas in Sonoma County that will have different permitting responsibilities depending on slope due to the recently adopted Sonoma County Vineyard Planting and Replanting Ordinance (upper map). We are currently using spatially explicit models to identify areas that may be more suitable for vineyard development based on recent trends in vineyard expansion (lower map). The pattern of vineyard development is influenced by physiographic, environmental, and land-use variables.

In summary, are examining changes in oak woodland connectivity, effects of changing environmental policies, and areas of land-use conflict are examined to strive for sustainable agriculture on a landscape scale.

Prepared May 1999.