Dina, you have to phrase your  Question more precisely. Broad-leaf versus coniferous? Or mixed coniferous/broad-leaf? Evergreen or deciduous broad-leaf. And not associate climate ("subtropical") with life form. 

Once clarified the above we may address the diversity.

Technical Report Vegetation Classification; a review for harmonization of maps

Thank you, i plan to do research in mixed coniferous-broadleaved forest , particularly in mixed broadleaved-korean pine forest, however first i would like to do brainstorming about this ecosystem and its issue/problem focus. I will state my question clearly. Thanks for the reference.

I found your paper on RG describing the forest site. All the mentioned east Eurasian tree species are from palaeartic genera (Pinus, Abies, Acer, Betula,Tilia, Ulmus) that have related (vicarieting) species in western Eurasia and North America.  In order words, there is a large body of literature you may consult on the diversity of such mixed coniferous/broad-leaf, deciduous forests.

A few observation to get you started. These six tree genera are usually not occurring together within a single forest site in western Eurasia. Generally, the  plant biodiversity (species richness; endemism) in forests dominated by the mentioned genera is mostly higher on the forest floor rather than in the tree layer. In contrast, in the equatorial forest, the diversity is usually higher in the tree layer, including arboreal orchids and liana.

thank you very much for your kind explanation, i have just did surveying in mixed coniferous/broad-leaf forest in Northeast China, as you mentioned, generally those genera are found. Now am trying to recognize the problems in this kind of forest also learn about plant communities. thank you