I have heard that the Appalachian Mountains is qualified as a temperate rainforest. What qualifies a temperate rainforest and what makes the Appalachian Mountains a temperate rainforest?
The definition of temperate rainforest is rather vague and varies around the world, but in general they are forests well away from the tropics which have a mild, damp climate, and prolific rainfall. Trees can be coniferous, evergreen broadleaf or deciduous broadleaf. Welsh rainforest (I prefer to call it woodland) is mainly deciduous oak, and rather bleak in winter. I have no experience of Appalachia, but I do have experience of rainforest in the west of Britain and rainforest in Malaya and Borneo, so I'm in a good position to make a comparison.
Anyone hoping to see rainforest in Britain which bears any resemblance to the rainforests of Malaysia will surely be disappointed, though in some other parts of the world there are temperate rainforests with a sub-tropical flavour. This is not to say that in UK rainforests there is nothing worth seeing. There is quite a lot, particularly in summer, and the same is probably true of Appalachian rainforests. Our UK rain forests are particularly rich in lichens, for those with an interest in lichens. Unfortunately some British rainforests are in danger of being taken over by rhododendrons, which are an invasive species and not native. Tropical rainforests are incomparably richer in species, plants as well as animals, but have the disadvantage that they are also far more dangerous.