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Most likely, you’re going to see a degree of overlap rather than a hard and fast boundary. Rainforests are principally defined by the climate in which they exist; high precipitation and generally moderate variation in temperature are the key factors. Normally, climate zones don’t simply end, they blend, unless there is some geographical feature (like a mountain range) that creates a distinct microclimate. Think about it this way – you don’t often see a lush field that gets rainfall every day just across the road from a desert. The progression is gradual. So what you’ll see is a wet area that gradually tapers off along the edges, and within that marginal zone, you’ll get a mix. The more moisture tolerant species of the “normal” forest will intrude further into the rainforest area than the ones that need dryer soil, and the less water dependent species of rainforest plants will expand into the range of the normal forest. You see the same thing happen with temperature as you go up a mountainside. More cold tolerant low-land trees climb up the slope higher than the warmth-dependent ones and vice-versa. I hope that makes some sense.
As for what to call this type of forest, I’m not quite sure what you are looking for. There are lots of types of forest, depending on the type of climate, vegetation, etc. But since you mention broadleaf, I’m thinking the term you want is deciduous, which is essentially the corollary to coniferous. Trees such as oak, elm, etc would fall in this category.
Hopefully this will be of some use to you; if you want some specific reference resources, you might consider an atlas – most good complete atlases will have a section in the front that includes diagrams of dominant vegetation zones, so you can see what tends to border with what and in what climate regions.
Cheers,
Rumrunner
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"But as he gazed on truth his aching eyes grew dim...."
-- Byron, from Childe Harold's Pilgrimage, Canto the First
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