RESUMO
We investigated the characteristics of plant species diversity in tree and shurb layers and the main influencing factors in different slope positions of a shady slope of degraded tiankeng talus. The results showed that there were 21 species in 17 genera and 13 families in the tree layer, and 20 species in 20 genera and 14 families in shrub layer in the south side of the Shenxiantang. Plant communities were subtropical moist coniferous and broad-leaved mixed forest. Micro-climate led to obvious vegetation variation between the pit and the pit slope at the tiankeng. The secondary collapse over the talus with mid-slope could conserve more water, which supported the water-demanding species in a high-quality niche. All the α diversity indices including Margalef (3.58), Shannon (2.47), Simpson (0.79) and Pielou (0.86) reached the maximum at the pit bottom edge with slight variability, and the maximum coefficient of variation was only 0.226. The ß diversity index fluctuated greatly among the pit-pit, slope-pit, bottom edge. The Routledge and Whilson-Shmida indices showed the trends of decrease-increase-decrease, with the maximum values of 15.95 and 1.20, respectively. Species turnover demonstrated the upward trend overall, and the number of co-species was decreased. Plant diversity on each slope position was mainly related to the contents of total nitrogen, total phosphorus, available phosphorus and organic carbon in soil. Soil was the most important factor leading to the difference among slope positions.
