Extremely draught resistant Opuntia cactuses form arid shrub forests in the lowlands, particularly on the larger islands, like Santa Cruz. At higher elevations, the climate of the Galapagos Islands, Ecuador, is cooler and with more rainfall. As a result there is true forest on the higher mountains thanks to the cooling of the air as it is forced up. When the air cools off, the humidity in the air condenses, thus forming clouds.