Constructing Red Number for endangered plant species:
Israel flora as a test case
The main problem in conservation policy is to define the priority of a certain species to invest conservation efforts in a limitation of resources. We suggest a method of constructing red number for plant species, in order to set priorities in conservation policy. The Red Number is an additive index, summarize values of four parameters:
1. Rarity - The number of sites (one square kilometer) where the species is present. A rare species determined as a species present in 0.5% of the area or less.
2. Declining rate and habitat vulnerability - Evaluate the decreasing rate in number of sites and the destruction probability of the habitat.
3. Attractivity - following the flower size and the probability of cutting or exploiting the plant.
4. Distribution type - more emphasis given to narrower endemics and to peripheral species that are in the edge of their distribution, reflecting the importance and unique nature of peripheral populations.
The plant species of Israel were scored for the parameters of the red number. 373 species, 16.28% of the Israeli flora entered to the “Red List” receiving red number above 6. Out of the Red List, 273 species are Mediterranean, significantly over-represented comparing the whole flora of Israel. “Post Mortum” analysis for the 34 extinct species of Israel revealed average Red Number of 8.6, significantly higher than the average of the current Red List. Only 15 species were limited to one site before extinction, indicate that rarity is not the only factor of extinction in Israeli flora.