| Summary: | With the current loss of biodiversity, efforts are being amassed to prioritize biodiversity hotspots that should receive high conservation priority. These studies often compare different biogeogrpahical regions using absolute estimates of species richness or rarity. Consequently, arid, semiarid, and other areas (e.g., boreal) are often ignored or are undervalued. Here, using a regional case study, we propose and demonstrate an approach that enables us to determine plant-based hotspots over landscape units across biogeographical regions using normalized, and comparing with absolute, measures. Three botanical variables were calculaled for 521 predetermined landscape units in Israel. These included plant species richness, the sum of scores of red (endangered) species, and a spatial exclusiveness score, all calculated from the Israel Plant Information Center (Rotem) database. We classified the landscape units into six rainfall belts (from extreme-arid to mesic-Mediterranean), as a normalization method to enable comparison and ranking across different environments. Residuals from the species-area curves were calculated within each belt for each of the variables, as a means to normalize for sampling effects. The 25 highest-ranking landscape units were identified as botanic hotspots, both before and after normalization. Prior to normalization, most of the hotspots were located in the Mediterranean region. Following normalization, hotspots were identified across the entire climatic gradient and corresponded with threatened habitats where many threatened plant species exist, such as wetlands, sandy loamy soil, and heavy clayey soil areas. The use of rainfall belts enabled us to identify additional important conservation hotspots that are located in relatively poor species environments, such as deserts. This method should be further applied on a global basis to identify hotspots within additional biomes that have been mostly excluded from existing global hotspot maps, such as the Taiga, Boreal forests, Tundra, and the arid and semiarid desert and Xeric shrublands.
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