A great belt of deserts, including the Sahara desert, and Arabian desert, separates the Palearctic and Afrotropic ecoregions. These desert ecoregions are included in the palearctic ecozone; other biogeographers identify the ecozone boundary as the transition zone between the desert ecoregions and the Mediterranean basin ecoregions to the north. This would place the deserts in the Afrotropic, while others place the boundary through the middle of the desert.