In the tropical rainforest, only very little light is penetrating the forest floor due to to dense canopies. Epiphytes evolved a life strategy where they can catch more light by growing on trees, but therefore they are threatened by desiccation, as their roots don’t stick in the soil. In cloud forests like on this picture on Mount Kinabalu on Borneo at around 1800 a.s.l., epiphytes are surrounded by moisture all the time and can so grow in high numbers and diversity.