The han subgroups are generally groups which are categorized according to their respective chinese dialect such as Hokkien, Cantonese, Teochew, Shanghainese, Gan, Wuhan dialect, Sichuan dialect, Mandarin etc.
Chinese language is generally divided into 7 major groups. 6 dialect groups are from the south while only Mandarin is from the north. However, you can even subdivide the major linguistic groups into sub-dialect groups. For instance, Hokkien (Minnan), Teochew, Fuchow, Putian etc are all classified under "Min" group.
Under "Mandarin", you can subdivide it into Beijing Mandarin, Nanjing Mandarin, Sichuan dialect, Shandong dialect etc.
For info about chinese Language groups, refer to
http://en.wikipedia.org/wiki/Chinese_languageThe various dialect groups (han-sub group) are what has caused cultural differences in different regions of China. There is also differences in culture between north and south due to different dialects spoken. That means to say regional culture in China was developed due to the different dialects spoken in a particular region.
QUOTE
What Han subgoup(s) are native Mandarin-speakers?
Strictly speaking, the standard Mandarin is currently based on Beijing accent. Thus, beijing chinese are considered to be 'native Mandarin speakers". However, the northerners generally speak Mandarin but with varying northern dialect tones.
There are now also many southern chinese who speak Mandarin at home and are considered to be native Mandarin speakers. Their mandarin are considered to be 'less standard' as compared to Beijing standard.