Effects of habitat fragmentation on the demography of the critically endangered tree Pterospermum kingtungense (Sterculiaceae) in Yunnan, China

We compared the demographic structure and reproductive output of the critically endangered tree Pterospermum kingtungense population in different size forest fragments (5-ha and 15-ha) and continuous forests in southwestern China. Specifically, we tried to answer the following questions: (1) are habitat fragmentations affecting the population demographic structure? (2) Do the plant reproductive outputs vary in the different size forest fragments compared with continuous forests? Within each of the three habitats, three permanent demographic plot of 50 m × 100 m in size were established and surveyed. We found that the density of P. kingtungense is relatively higher in the 15-ha fragment and continuous forests than in the 5-ha forest fragment, but the difference is not significant in the three habitats. Large trees (dbh ≥ 15 cm) were significantly higher in continuous and 15-ha forest fragments than that of the 5-ha forest fragment, whereas no seedlings occurred in the 5-ha forest fragment. The flowering proportion of the P. kingtungense populations was also lower in the 5-ha fragments than that of 15-ha fragment and continuous forests. During the investigation, no flowering occurred in the 5-ha forest fragments for two consecutive years, indicating that habitat fragmentation has an effect on the reproduction of the population. Due to the self-compatible of the species, the fruit and seed settings of the two types of forest fragment were similar to that of the continuous forests. Our findings showed an alteration of basic underlying demographic properties due to forest fragmentation, which may influence the population dynamic of P. kingtungense.