Rarity Weighted Richness Index, ACE-II (Areas of Conservation Emphasis), Great Valley Ecoregion, California

California Dept. of Fish and Game ecoregional analyses of rarity weighted richness by 2.5 square mile hexagons, for ACE-II project, 12.2009. NOTE: update expected in August 2015. 

(See Limited Data Hexagons dataset for additional information:  http://databasin.org/datasets/6245235a90cd463398d14276f237c855)

Four indices of biological richness were developed: total native species richness based on species range maps, rare species richness and rarity-weighted richness based on rare species occurrence data, and sensitive habitat presence. The four indices were combined in a weighted-additive model framework, giving each index equal weight, to produce the ACE II biological index surface. Hexagons with a high biological index score represent those areas with high species richness, high levels of rarity and irreplaceability, and/or sensitive habitats. The biological index was calculated separately by USDA Ecoregion section, to identify the areas of highest richness and rarity within each ecoregion of the state. Because each ecoregion was analyzed separately, the biological index surface is meant to be viewed only one ecoregion at a time; biological index scores are not directly comparable between ecoregions.The ACE-II biological index is a broad-scale analysis and does not incorporate all biological considerations that should be addressed during comprehensive conservation planning, such as threats to natural habitats, level of habitat conversion (i.e., urbanization), intactness and connectivity, or current level of protection. It should not by itself be interpreted as a map of conservation priorities. See the ACE-II Project Report for a detailed description of data inputs and analyses at https://nrmsecure.dfg.ca.gov/FileHandler.ashx?DocumentID=24326. An abbreviated summary is provided below.To depict biological richness, four indices relevant to conservation value were produced: native species richness, rare species richness, "irreplaceability" (i.e., rarity-weighted richness), and the presence of sensitive habitats. Native richness and rarity layers were developed for each of six taxonomic groups: birds, fish, amphibians, plants, mammals, and reptiles. The data were then combined across taxonomic groups to produce total native species richness, total rare species richness, and total rarity-weighted richness indices. The data were normalized to give each taxonomic group equal weight, to remove any bias caused by the variation in the total number of taxa per taxonomic group.For ecoregional analyses, data were normalized by ecoregion, and for statewide analyses data were normalized statewide. Information on the location of four sensitive habitat types, wetlands, riparian, rare upland natural communities, and high value salmonid habitat, was also assembled. Final data sets were ranked ecoregionally and statewide by quintile. Raw ecoregional index values are provided, as well as ecoregional and statewide ranks for each index. Note that hexagons may have a low ecoregional ranking but a high statewide ranking. For example, in the Klamath Mountains Ecoregion, which has very high overall native species richness, even hexagons with the lowest relative ecoregional native richness (Native Species Richness Ecoregional Rank=1) have high native richness values with respect to the rest of the state (Native Species Richness Statewide Rank=4 or 5). The Statewide Rank was not incorporated into the ecoregional analysis, but may be an important consideration during planning.The four indices of richness and rarity were combined in a weighted additive model, giving each index equal weight, to produce the ACE II biological index surface. Hexagons with a high biological index score represent those areas with high species richness, high levels of rarity and irreplaceability, and/or sensitive habitats. The biological index was calculated separately by USDA Ecoregion section, to identify the areas of highest richness and rarity within each ecoregion of the state. Because each ecoregion was analyzed separately, the biological index surface is meant to be viewed only one ecoregion at a time; biological index scores are not directly comparable between ecoregions.Areas with a high biological index score would be expected to have high conservation value and meet multiple conservation goals. However, data included in ACE II are subject to certain assumptions and limitations that must be considered in any use or application of the data. The biological index surface is limited by the accuracy and scale of the input data, and does not represent all areas of high biological value throughout the state. Some areas with a high biological index score may have low biological or conservation value due to habitat conversion (e.g., urbanization) or other factors.The ACE-II biological index is a broad-scale analysis and does not incorporate all biological considerations that should be addressed during comprehensive conservation planning. It should not be interpreted as a map of CDFG's conservation priorities. Current level of protection, level of habitat conversion (i.e., urbanization), intactness and connectivity, and threats to natural habitats, all important considerations when determining conservation value, were not considered when developing the biological index. The biological index surface is not a delineation of the reserve configuration needed to ensure adequate protection of individual species or habitats. The biological index does not replace site-specific evaluation of biological resources and should not be used as the sole measure of conservation priority during planning.