The Upland Habitat Goals Project integrated geographic stratification by defining subregions referred to as landscape units (see map below). The nine-county San Francisco Bay Region was divided into 34 landscape units. In delineating the landscape units, the emphasis was on creating geographically coherent units, but limiting landscape units to a reasonable number to keep the analysis tractable.
It is essential for a conservation plan to protect target species in all environments where they occur – across latitudes, elevations, aspects, etc. – to build in redundancy and resilience. In developing the Conservation Lands Network, goals were established for each vegetation type within each landscape unit where it occurs, thereby incorporating much of the ecological variability within a vegetation type along regional climatic and biogeographic gradients. For example, blue oak should be protected in the farthest western reaches where it is found as well as in the East Bay where it is quite abundant. Capturing such geographic stratification is likely to capture genetic variability and provides multiple representations of conservation targets, both of which bolster resilience in the event of major habitat loss, rapid climate change, or other disturbance.
Demarcation of the landscape units followed major physiographic features, primarily mountain ranges and intervening valleys. Discrete mountain ranges such as Mt. Diablo, Sonoma Mountains, Southern Mayacamas, and Marin Coast Range each became individual landscape units. Where discrete valleys do not exist, major highway corridors were used to subdivide mountain ranges, as in the cases of the East Bay Hills landscape units (Highway 24, I-580, and I-680), Santa Cruz Mountains Landscape Unit (Highway 17), and American Canyon Landscape Unit (Highway 12). Major valleys such as Napa, Sonoma, and Santa Clara were delineated manually using slope and topography derived from the USGS 10m Digital Elevation Models.
The urban plains around the Bay were divided into four landscape units labeled urban – San Mateo, Alameda, Contra Costa, and Santa Clara – and excluded from the coarse filter analysis that led to the initial draft Coarse Filter Conservation Lands Network. However, because streams are important conservation targets and traverse urban areas, the project recommends the protection and restoration of stream conservation targets along their entire length including within the urban landscape units. A fifth landscape unit excluded from the study area is the San Francisco Bay and Baylands, because the baylands are covered by the Baylands Ecosystem Habitat Goals Project, and the submerged tidelands are the focus of the San Francisco Bay Subtidal Habitat Goals Project.
Protected areas within the San Francisco Bay and Baylands Landscape Unit and adjacent to the Upland Habitat Goals Project boundary were reviewed for connections to the Conservation Lands Network. Similarly, the CLN was reviewed at the outer county boundaries, and adjusted to ensure connections to protected areas adjacent to, but outside of the study area.
Watersheds were considered as an option for designating distinct geographic units, but were not selected for several reasons. Watersheds are delineated by ridgelines, but upland areas are better defined by entire mountain ranges. Watersheds also often extend across natural physiographic features such as mountains with valleys, and thus do not capture important components of integrity within these distinct areas. However, the Riparian/Fish Focus Team members selected watersheds as the logical geographic unit for reviewing coverage for fish and stream conservation targets by the Coarse Filter Conservation Lands Network.