What determines the set of altitude zones?

Since the air temperature decreases with height, different natural zones are formed on different parts of the mountain slope. This phenomenon is called altitude zoning. The higher the mountain and the closer it is to the equator line, the more different natural zones can be found on it. Take the Himalayas as an example. The southern slopes of these mountains are in the tropical zone, and rainforests are formed there. Then deciduous and coniferous forests, alpine meadows, tundra and a zone of ice deserts appear.