In Morrowind, Cyrodiil is described as both a "jungle" and a "rainforest". The game also makes note of Deciduous trees--that is, trees that shed their leaves. When speaking of Valenwood, however, the authors made a point of calling the forests in southern Elsweyr as "tropical rainforests". This is when the revelation struck me: Aha! I said, the Cyrodiil team has it all wrong! Oblivion's temperate Cyrodiil wasn't a retcon of its aforementioned "jungles" or "rainforests". It was a temperate rainforest, very much like those along the west coast of North America and elsewhere around the globe. Sure, the vegetation could have been denser (Bethesda was limited to using an outside utility for generating their forests, though) and perhaps it could have rained more (but really, who wants that? XD), but it is clear to me now that Bethesda stayed pretty close to the original lore. And jungle can really just refer to an area with dense vegetation.
I came into the series with Oblivion...so perhaps I'm ignorant of lore that said otherwise.
Thanks and good luck with Stirk!