the number of herbivore and mammal species numbers within a given area. The index is also used in studies of climate change. Thermal classifications within the Thornthwaite scheme include microthermal, mesothermal, and megathermal regimes. A microthermal climate is one of low annual mean temperatures, generally between and which experiences short summers and has a potential evaporation between and . A mesothermal climate lacks persistent heat or persistent cold, with potential evaporation between and . A megathermal climate is one with persistent high temperatures and abundant rainfall, with potential annual evaporation in excess of . See also Ecological land classification Biogeographical realm Biome Geographical zone Hardiness zone Mediterranean climate or dry summer climate References Climate and weather classification systems