Thanks everyone for the supportive comments!

Geogramatt, good point about change in land-use and livelihoods, which is certainly a more immediate and dramatic change than that it climate.

Yiyannanjin, there's not an easily available guide to rhododendrons of Yunnan, as you suggest mostly because of the incredible richness of species.

There is a guide in Chinese that's available sometimes in the Zhongdian bookstores, called something like "The wild ornamental plants in the three parallel rivers", that's pretty good for flipping through and at least getting to genus, although it won't often have the exact species that you're looking for. Another book with superb photos and good coverage of Yunnan rhodos is "Guide to the Flowers of Western China" in English from Kew Press, but its cost and weight are both heavy.

If/once you know what genus you're looking at, the Flora of China available for free, online at www.efloras.org/flora_page.aspx?flora_id=2 . Looking through a botanical key can be a bit daunting, but there are names, elevation ranges, illustrations along with the more detailed descriptions.

Each of these works will also have good details on begonias, orchids, and the other taxa that Yunnan is famous for (primula, pedicularis, etc.)