| Abstract: | The geoecological conditions of Xizang (Tibet) are very complicated. An approach on the floristic phytogeographical differentiation of Xizang has been made in the present paper with a quantitative floristic method. According to areal types of the species the flora of Xizang may be classified under five major geoelements: the north temperate zone geo-element (N), the Central Asiatic geoelemcnt (C), the Qinghai-Xizang Tibetan Plateau geo-element (T), the Sino-Himalayan geo-element (SH) and the tropical geo-element (Tr). Different diagrams of spectra of floristic elements of Xizang are presented. Four cross-sections were chosen for illustrating the regional differentiation of spectra of floristic elements of Xizang. It is obvious that the SH-geo-element prevails in the Eastern and Southeastern Xizang and the Trgeo-element is confined at lower elevation of the southern flanks of the Himalayas. On the contrary, on the Plateau proper the Tgeoelement dominates and the C-geo-element plays a significant role in the northwestern part of Xizang. It corresponds to the following horizontal zones of vegetation from southeast to northwest: montane forest-alpine meadow-alpine steppe-alpine desert. An example at the southern slopes of the Eastern Himalayas has been taken to investigate the vertical variation of the spectra of floristic elements, the boundary between the both subbelts of the montane evergreen broad-leaved forest belt at an elevation of 1,800 m has been proposed as the upper limit dominated by the tropical geo-element. On the basis of dominance spectra of the fioristic elements in the grid-square system floristic boundaries are defined, which separate different floristic regions from one another, thereafter a floristic division of Xizang has been discussed. There are the sub-region of the "Himalayan flanks belonging to the Indo-Malaysian sub-kingdom of the Palaeotropical kingdom, the Sino-Himalayan sub-kingdom and the Qinghai-Xizang Plateau sub-kingdom of the Holarctic kingdom. |
