Trolls need the mountain areas, dwarves need mines and whatever the species there has to be a source of clean water, which is unlikely to dry up. Even more crucially the lakes that feed the Fountain of Youth in the Queen's Palace grounds must never dry up given all fairies must drink from this fountain regularly to top up their "in the blood" natural powers. The Kingdom's fairies could be killed off by draining this fountain and what feeds it.
Incidentally other species are known to drink from the fountain. They don't get the benefit of magical rejuvenation but the water is renowned for its wonderful, sweet taste and even the witches love it. (The more friendly they are to the Queen and fairies generally the more likely they will be allowed to use the fountain sometimes. It is not worth trying to get around the Palace guards and spells set up to defend the Queen. Beings die when they do that).
Landscapes of course dictate what kind of species can live there as is the case with life on Earth. Fresdian has made a huge study of this and has collected photos from Earth of some of the scenery she has seen and admired there.