Abstract:

The arid hardwood forests in mountainous region is distributed in the upper edge of dry-hot valley of Jinsha River in Southwest Sichuan, in which, Castanopsis delavayi is one of the main constructive species. C. delavayi forest is typical arid hardwood forest. By the investigation of seed rain pattern and seed bank dynamics on the earth's surface during seed rain, and the seedling situation in two low density populations of C. delavayi in mountainous area in Southwest Sichuan, the seed productions, seed retentions and their contributions to seedling establishments were discussed. The results showed as follows: 1) the duration of seed rain was above 2 months, but there was a different top time of seed fall between the studied plots. 2) the seed production of C. delavayi was low in the studied area, seed rain had a low dispersing density (2.3 to 2.8 grain·m ^-2). 3) in the whole process seed rain, the decayed and germinating seeds in the seed bank were never found. The sound seeds and the damaged seeds by insects were slightly fluctuated. The retaining density of sound seeds was 0.13 grain·m^-2, on the contrary, there were accumulative effects of cups and aborted seeds on the earth's surface. Therefore, various constituents of soil seed bank had different dynamics. 4) the retention rate was only 8.7% and 2.17% of dispersing seeds, which was the main cause of soil seed bank losing, 91.3% lost in population 1 and 97.83% lost in population 2. 5) three key links I. E., the low seed production, the low seed retention in soil seed bank and difficult establishment of seedling, limit the population regeneration of C. delavayi.

Key words: Castanopsis delavayi, seed rain, seed bank of soil, mountainous area in Southwest Sichuan