- Metric Name:  Beta Diversity

- Data Vintage:  2021

- Unit Of Measure: Sørensen index, 0 to 1

The number of species that are not the same in two different environments; functional groups and vegetation communities. Beta diversity is a valuable complement to species richness due to its ability to link local-scale changes in species occurrence to landscape-scale shifts in patterns of species composition. Beta diversity measures changes in species composition by comparing species richness and species presence in one locality to all localities within a specified neighborhood size or among specified areas of interest. Localities exhibiting high beta diversity are distinctly unique in terms of species composition as compared to other localities used for comparison. Unlike species richness, beta diversity provides a measure of species composition that can be used to help identify localities which may harbor rare species, localities which could be sources for landscape-level diversity, and regions of either high heterogeneity or homogeneity. Calculated through time, beta diversity can also detect trends in diversity (i.e., loss or gain of heterogeneity among sites) or detect areas in which species composition changes very little.- Creation Method:  This has been generated using the California Wildlife Habitat Relationships model developed and managed by the California Department of Fish and Wildlife. The beta diversity index used is the Sørensen index. It is an occurrence-based measure of dissimilarity between species composition of two communities, one at the pixel scale and the other across all the other pixels within the associated 3,000m window. It is calculated as the sum of the number of species in each community, divided by two-times the number of species common to both communities plus the sum of the number of species in each community.

DSC = (S1+S2)/2c+S1+S2

Where c = species in common, S1 = species in community 1, and S2 = species in community 2.

Larger values represent greater differences among the two communities, and therefore greater beta diversity.

- Credits:  --	Forest type designation (FORTYPE) from Forest Vegetation Simulator (FVS) F3; 2021

--	National Land Cover Database (NLCD); 2019

--	Existing Vegetation (CALVEG), Region 5, MARS Team; 2016

--	California Department of Fish and Wildlife CWHR version 9.0 (CDFW); 2014