Technical Abstract: The Mediterranean-type biome is rich in biological diversity and species endemism yet it supports large centers of human population and agriculture. Wine-grape production constitutes a major land use in this biome, and the mosaic of vines and native plant communities found in vineyard landscapes represents an opportunity for multi-use management that can provide carbon (C) storage, greenhouse gas mitigation, biodiversity protection and crop production. This study evaluated C stocks and woody plant diversity across vine tracts and adjoining woodland ecosystems (wildlands) for organic vineyard lands in Mendocino County, California. Aboveground C in woody biomass was estimated from 93 vegetation plots (30 x 10 m) using field measurements combined with published allometric equations. Soil C was also estimated from samples collected in 1 m-deep soil profiles from 44 soil pits. The sample measurements were combined with physical variables associated with their locales to model total C stocks across the landscape using a geographic information system and multivariate linear regression. The results showed that on average, wildlands stored 32.8 Mg C/ha in aboveground woody biomass and 90.9 Mg C/ha in soil, compared to vineyard tracts that stored 2.1 and 84.1 Mg C/ha, respectively. Although the heterogeneous landscape presents modeling challenges, the results are unequivocal in showing greater C storage in wildlands, as well as higher richness in native plant diversity relative to vineyard tracts. Together, these facts argue for the conservation and valuation of wildlands within agricultural landscapes—a management approach that may require revisions to current C incentive programs if agricultural landowners are to have sufficient motivation to maintain the integrity and ecosystem services of their varied landscapes.