Latitudinal patterns in geographical elements of woody plants in a karst area of southwestern China

Three representative distribution areas of native karst vegetation were surveyed, including Nonggang and Longhushan Nature Reserves respectively located in the northern tropics and southern subtropics of Guangxi Province and Maolan Nature Reserve situated in the central subtropics of Guizhou Province. Woody plant species in the three regions were determined according to field surveys and literature review, with their latitudinal variation and floristic composition then analyzed. The categories of woody plants in the three climatic zones were as follows:104 families, 425 genera, and 936 species in Nonggang; 99 families, 363 genera, and 636 species in Longhushan; and 100 families, 352 genera, and 995 species in Maolan. The woody flora was dominated by tropical and subtropical components, and the tropical nature of the dominant families gradually decreased with increasing latitude. The ratio of tropical floristic components to temperate floristic components (R/T) reflected the tropical nature of the woody flora of Nonggang and Longhushan Nature Reserves, whereas the ratio value was much lower in Maolan Nature Reserve, indicating that the proportion of genera with temperate characteristics increased with latitude. The similarity coefficients at the family, genus, and species level indicated that the woody plants of Nonggang and Longhushan were closely related, followed by those of Nonggang and Maolan, and finally those of Longhushan and Maolan, which were relatively distantly related.