It has been found that floristic patterns are strongly associated with geographical (particularly latitudinal) factors in local floras across China.Prof ZHU Hua of Xishuangbanna Tropical Botanical Garden (XTBG) used a database of 135 regional floristic works covering the areas of southern China south of 30°N to illustrate the distribution patterns of their floristic elements.
By analyzing the distribution patterns of geographical elements of seed plants from an updated database of regional floras in southern China, the researcher discussed the boundary of the tropical zone of China biogeographically. The study was also concerned with the palaeovegetation patterns of China from the implications of the distribution of geographical elements of seed plants.
The study found that the tropical geographical elements of seed plants contributed a majority to regional floras in southern China. Their frequencies decreased in proportion with increasing latitude. The frequency patterns illustrated several demarcations. The areas for which tropical genera account for > 80% of the total genera in the flora are south of 22°30′N in southern and southeastern China, which corresponded closely to the northern boundary of the tropical monsoon forest and rain forest in southeastern China. The line at c. 22°30′N was therefore suggested to be the northern biogeographical boundary of the tropical zone in south and southeastern China.
South of 22°30′N, tropical plants, such as coconuts, rubber trees, coffee, jackfruits, pepper etc., could generally survive the winter without cold protection. The line was far north of the northern boundary of the marginal tropical climate, which implied that the tropical zone extended further north during geological history. It’s concordant with the palaeoecological studies that suggested the northward shifts of tropical and subtropical broadleaved evergreen forest in eastern China during the mid-Holocene.
The study entitled “Geographical elements of seed plants suggest the boundary of the tropical zone in China” has been published online in Palaeogeography, Palaeoclimatology, Palaeoecology, http://dx.doi.org/10.1016/j.palaeo.2013.04.007,
