Nepal contains a disproportionately large diversity of plants and animals, relative to its size. Nepal, in its entirety, forms the western portion of the eastern Himalayan biodiversity hotspot, with notable biocultural diversity. The dramatic differences in elevation found in Nepal (60 m from sea level in the Terai plains, to 8,848 m Mount Everest) result in a variety of biomes. Eastern half of Nepal is richer in biodiversity as it receives more rain, compared to western parts, where arctic desert-type conditions are more common at higher elevations. Nepal is a habitat for 4.0% of all mammal species, 8.9% of bird species, 1.0% of reptile species, 2.5% of amphibian species, 1.9% of fish species, 3.7% of butterfly species, 0.5% of moth species and 0.4% of spider species. In its 35 forest-types and 118 ecosystems,{{efn|198 ecological types were first proposed in 1976, which was further revised and reduced to 118, which was further reduced by IUCN to 59 in 1998, which was further reduced to 36 in 2002. As this issue has yet to be settled, the 35-forest-type classification is generally preferred to the ecological categorization.}} Nepal harbours 2% of the flowering plant species, 3% of pteridophytes and 6% of bryophytes.