Abstract:

Yuanjiang dry-hot valley is a poorly vegetated and fragile arid ecosystem in low land. Although it was lushly forested before the middle of the 17^th century, it became a tropical montane savannah after the end of the 17^th century. This study focuses on the diversity and distribution patterns of plants in this representative xerophytic flora, aiming to explain the impact of main environmental factors such as temperature, precipitation and underground water supply on species and populations, so as to explore the adaptation of plants. Furthermore, dry-hot environment indications corresponding to species and species assemblage were considered. Therefore, alpha and beta indices were employed to cope with biodiversity differences in plant species and its environment, respectively. Selected indices were subscribed to the relationship among species, population size, and their living circumstances in terms of Species_estimated, Singletons, Uniques, ACE, ICE, and Chao2. The results show that: (1) alpha diversity is higher in the transects and plots closing to the river channel (< 25 m), and decreases away from the riverway; (2) beta diversity increases from upper to lower stream in L-transect (Bray-Curtis < 0.500), however, it is reversed in P-transect, the homoplasy is obvious (Bray-Curtis > 0.500); (3) in the lowland of dry-hot valley, indices of Species_estimated, Singletons, Uniques, ACE, ICE, and Chao2 are significantly high beside river especially in the tidal range, which indicates a strong reliance on water supply. Conclusively, species composition and distribution patterns in the lowland of Yuanjiang dry-hot valley are deeply affected by heterogenity of water and temperature allocation. Plant species and their diversity are closely correlated to the microhabitat along river channel, and this correlation could be an approach for environmental monitoring potentially.

Key words: Yuanjiang dry-hot valley, lowland, biodiversity, species distribution, indicator species, Yuanjiang-Red River