Biodiversity Data Layers and Priorities
From its inception, the Partnership has recognized the importance of preserving biodiversity as a key component of its overall vision to conserve the region.  More recently, as a greater understanding of the area's ecological resources has been developed, the significance of the BRBNA's biodiversity has been shown to be even greater than originally thought.  Through extensive vegetation mapping and analysis conducted between 2000 and 2004, the Information Center for the Environment (ICE) and Natureserve (a national organization that promotes the preservation of biodiversity) have documented major concentrations of rare species, globally significant plant communities and areas of high biodiversity in the BRBNA.

What is biodiversity?  The term has become widely used in conservation circles, most correctly as it refers to the variety of life forms in a given area:  the different plants, animals and microorganisms, their genes and the ecosystems they inhabit.  While considerable efforts have focused nationally and globally on the preservation of biodiversity for several decades, we continue to lose plant and animal species at an excessive rate.  According to the most comprehensive study done to date, over a million species will be lost in the coming 50 years.  The scale of global extinction of species that occurred in the 20th century was at a rate a thousand times higher than the average rate during the preceding 65 million years (Jaan Suurkula, M.D. and chairman of Physicians and Scientists for Responsible Application of Science and Technology).

Method
GIS data layers were created and combined to build the final biodiversity priorities map. Each of these layers and the method used to create the layer are described below:

Serpentine Soils
Serpentine soils are highly unique and support sensitive plant communities that include a range of rare and endemic plant species not found on other types of soils. Serpentine soils were identified using the SSURGO soils data and are illustrated in Figure 5-2: Serpentine Soils. All areas of serpentine soils were assigned a ranking of 5.

Streams
Streams are important indicators of biodiversity. Streams were classified as perennial and seasonal and buffered to indicate the highest value stream conservation areas. Perennial streams received a 100m buffer and seasonal streams received a 50m buffer as illustrated in Figure 5-3: Buffered Streams. All streams received a ranking of 5.

Water Bodies
Water bodies are also key biodiversity indicators. Water bodies received a 100m buffer as illustrated in Figure 5-4: Buffered Water Bodies. Water bodies include the major water bodies such as Lake Berryessa, Indian Valley Reservoir and Clear Lake as well as stock ponds mapped from aerial photographs. All water bodies received a ranking of 5.

CNDDB Occurrence Density
The CDFG oversees the California Natural Diversity Data Base (CNDDB). The primary purpose of the CNDDB is to gather and disseminate data on the status and locations of rare and endangered plants, animals, and vegetation types in order to conserve California's biodiversity. CNDDB data is point data based upon recorded field observations of rare and threatened species. Polygons estimating spatial reliability of a species sitings are applied to the area around these points. Larger polygons indicate a less accurate placement and were given a ranking of 4. Smaller polygons indicate accurate species location and were given a ranking of 5. Figure 5-5: California Natural Diversity Data Base Species Occurrence indicates areas of greater certainty of species occurrence in dark green and areas of lesser certainty of occurrence in light green.

Priority Vegetation Types
The Manual of California Vegetation identifies and describes the vegetation communities that occur throughout the state. Twenty-two vegetation types that occur within the BRBNA were selected and prioritized for use in the biodiversity model. The highest priority vegetation types were assigned a priority of 1 and a value of 5 due to their rarity and/or ability to sustain rare, threatened and endangered plant and animal species. These are:

• McNab Cypress Alliance
• Brewer Willow Alliance
• Serpentine Barren
• Sargent Cypress Alliance

On Figure 5-6: Priority Vegetation Types, the areas with the highest priority vegetation types are indicated in dark green. Black indicates areas where no priority vegetation types occur.  The lighter colors are areas with lower priority vegetation types. Additional vegetation associations and alliances were assigned a priority of 2 through 5 and a value of 4 through 1.

Road Density
Road density is measured by the length of road per square kilometer. Areas with the lowest road density, illustrated in dark green in Figure 5-7: Road Density, are considered less disturbed and provide a wider land area for large species to move without disturbance.

Vertebrate Species Suitability
The California Department of Fish and Game's (CDFG) California Wildlife Habitat Relationships (CWHR) data system is a wildlife information system and predictive model for California's regularly occurring birds, mammals, reptiles and amphibians. CWHR was queried to identify the vertebrate species that occur within the BRBNA Conservation Framework Study Area. This resulted in a subset of species that were used for habitat suitability modeling, based on their degree of rarity, endangerment or trend. The modeling was based upon three amphibians, six reptile species, 21 bird species and 13 mammal species.

The advantage of the CWHR vertebrate data layer is that it compensates for the data voids and false negative occurrences of target species found in the California Natural Diversity Data Base data. This allows for more continuous maps of biodiversity distribution.

Because the CWHR data is not directly compatible with the vegetation mapping completed for the BRBNA, the 57 vegetative cover types and 7 human-dominated cover types used for the vegetation map were translated into 26 and 4 CWHR habitat types for use in mapping and analysis.

Each species' suitability was determined using habitat type, canopy cover density, and stem size (the latter, only if tree-dominated) attributes to determine three suitability ratings: one each for forage, cover, and reproduction for that species. These three suitability layers were combined (using a geometric mean) into a single habitat suitability map for each species. If any one of the three suitability factors for a species were missing, that polygon was determined to be unsuitable for that species.

Eight separate maps were created to conduct this analysis - two maps each for mammals, reptiles, amphibians and birds. Maximum and mean value analyses were conducted for each group. For each of these four groups, the maximum analysis indicated the areas most suitable for protecting one or more species while the average analysis indicated the areas most suitable for the most species in that group. Each maximum and mean species layer was reclassified to values of 1-5 based on their modeled values.

Biodiversity Priorities
Using the data and information described above, weights were assigned to each data layer above to create the biodiversity conservation priorities map. These weights (and the rankings in the previous step) were assigned in order to develop a general biodiversity priorities map. Different rankings and weights could be assigned and a different map would result. To create Figure 5-9: Biodiversity Conservation Priorities, the following weights were used:

Highest Weighting

• Priority Vegetation
• Amphibians Average (Figure 5-8b)
• Reptiles Average (Figure 5-8d)
• Birds Average (Figure 5-8f)
• Mammals Average (Figure 5-8h)

Moderate Weighting

• Serpentine Soils
• Buffered Streams
• Buffered Lakes

Lower Weighting

• Road Density
• CNDDB Data
• Amphibians Maximum (Figure 5-8a)
• Reptiles Maximum (Figure 5-8c)
• Birds Maximum (Figure 5-8e)

Using these weights the areas indicated in the darkest shade of red in Figure 5-9: Biodiversity Conservation Priorities are key areas to conserve for biodiversity. From north to south these areas are:

• Walker Ridge
• Wilson Valley
• McLaughlin Reserve
• Knoxville OHV Area
• Cedar Roughs

Some of these areas are already in public ownership or have been permanently protected as part of the UC Natural Reserve System or through land trusts. Other areas such as stream corridors are in private ownership and do not have protected status.

In general the primary biodiversity conservation priorities indicated by the mapping and analysis are:

• Areas of suitable habitat for the greatest variety of wildlife species
• Rare and unusual plant communities
• Areas with known occurrences of rare, threatened and endangered plant and animal species
• Streams and water bodies and adjacent lands
• Serpentine soils
• Areas undisturbed by roads
• Other key factors related to biodiversity protection include:
• Lands that provide connectivity between already protected lands
• Areas adjacent to currently protected areas
• Private inholdings within public conservation holdings
• Large parcels in a single ownership
• Lands in close proximity to developed areas
• Lands that affect water quality in Putah Creek, Lake Berryessa, Indian Valley Reservoir, and Cache Creek, some of which are designated as impaired.
• Areas where multiple conservation objectives (biodiversity, working ranch and/or recreational) can be met simultaneously
• Lands subject to development threat