Abstract:

To explore patterns of plant diversity along altitudinal gradients on the west slope of Sejila Mountains, Tibetan, vegetation of different altitudinal gradients were investigated. Furthermore, we analyzed the reason of plant diversity patterns along altitudinal gradients. The results showed that there were 288 species, which belong to 58 families and 163 genera, on the west slope. There were four vegetation types, i.e. coniferous forest(3 000~3 200 m), dark coniferous forest(3 300~4 200 m), open forest or scrub(4 300~4 400 m), and alpine meadow (4 400~4 800 m) from low to high elevation. The altitudinal pattern of family, genera, species, shrubs, and herb species richness showed a double-humped pattern, while trees richness first increased and then decreased with increasing elevation, peaking at the altitudes of 3 300 m. Maximum values of Shannon-Wiener index and Simpson index occurred at the altitudes of 3 300 m, while maximum β diversity occurred at the altitudes of 3 500 m, and three diversity indexes were all the lowest at the altitude of 3 700 m. The altitudinal patterns of the ratio of number of species/number of genera and number of genera/number of family also showed a double-humped pattern, but the ratio of number of species/number of family increased with increasing elevation. We also found that the number of stems decreased with increasing elevation, maximum values of basal area and maximum DBH occurred at the altitudes of 3 900 m, while it occurred at the altitudes of 3 600 m for maximum height. The correlation analysis between species richness and environments showed that species richness was negatively correlated with elevation, and was positively correlated with slope aspect. The relationships between species richness and altitude and slope aspect could be described by different regression equations.

Key words: species composition, species diversity, altitudinal gradient, environment factors, Sejila Mountains