| Seed rain and seedling dynamics are two key ecological processes, affecting the structure,composition and natural regeneration of forest ecosystem.150 "seed trap-seedling plot" monitoring stations (refer to a seed trap and its three associated seedling plots) were established in a 20 hm2 forest dynamics plot in Parashorea chinensis forest in Xishuangbanna in late October 2007. The seed rain of 16 dominant tree species and the composition, spatial distribution, survival and recruitment of tree seedlings (DBH<1 cm) were monitored for one year from October 2007 to October 2008. The results were as following:1. A total of 1 640 seeds and fruits from the 16 dominant tree species in the plot were collected in one year, including 670 mature-intact seeds (40.85% of the total) which were.mainly the seeds of Sloanea tomentosa (36.57%), Pittosporopsis kerrii (13.88%), Garcinia cowa (12.39%) and Dichapetalum gelonioides (11.94%). The amounts and composition of seed rain varied greatly among the dominant tree species. The top four species with the most seeds and fruits collected in the seed traps were Sloanea tomentosa (826), Castanopsis megaphylla (156), Castanopsis echidnocarpa (108) and Pittosporopsis kerrii (106), while few seeds and fruits were captured in Knema furfuracea (3),Baccaurea ramiflora (0),Nephelium chryseum (4) and Diospyros hasseltii (2); Immature seeds and fruits were the major component of seed rain in the seven tree species(Parashorea chinensis, Pometia tomentosa, Diospyros hasseltii, Castanopsis echidnocarpa, Sloanea tomentosa, Castanopsis hystrix and Castanopsis megaphylla), while mature seeds comprised the major composition of seed rain in the eight tree species(Pittosporopsis kerrii, Garcinia cowa, Mezzettiopsis creaghii, Knema furfuracea, Phoebe lanceolata, Nephelium chryseum, Dichapetalum gelonioides and Pseuduvaria indochinensis). Tree species with large proportion of damaged seeds and fruits were Parashorea chinensis (44.00%), Castanopsis echidnocarpa (25.00%) and Castanopsis megaphylla (39.74%); For the cumulative seed rain of the 16 dominant tree species, the seed rain was mainly composed of immature seeds and fruits in the dry season (92.41%). However, mature seeds contributed to 66.73% of seed rain in the rain season. There were significant associations between the spatial pattern of seed rain and the distribution of their conspecific mature trees.2. The plot had relatively high tree seedling richness and differences in numbers of seedlings among species. In the first survey, among the 6 593 seedlings recorded,6 383 tree seedlings were identified to species, representing 49 families, 116 genera and 163 species. The seedlings had values of Simpson, Shannon-Wiener and Pielou indexes of 0.70,2.31 and 0.45, respectively. Species with less than 5 seedling accounted for 50.32% of the total number of species. At the I-m2 scale, seedling density and species richness were (14.18±0.71) ind.·m-2 and (3.78±0.10) sp.·m-2 (Mean±SE, n=450), respectively. Dominant species included Parashorea chinensis, Castanopsis echidnocarpa and Pittosporopsis kerrii, which showed different spatial distribution patterns that were closely associated with the topography, altitude and spatial patterns of their conspecific mature trees.3. In one year, mortality rate of seedlings recorded in the first survey was 37.05%, which was 23.28% and 13.77% in the dry season and rain season, respectively. Mortality rates varied widely among the dominant species, e.g., in one year, mortality rates were 80.72% and 55.42% for Litsea panamanja and Parashorea chinensis, respectively. However, low mortality rates (< 9%) occurred in the other five dominant species (Dichapetalum gelonioides, Knema furfuracea, Pseuduvaria indochinensis, Saprosma ternate and Garcinia cowa). In addition, for Litsea panamanja and Parashorea chinensis, relatively large proportion of the death occurred in the dry season (77.61% and 64.08%, respectively), while slight changes were detected between the dry season and rain season for other species.4. During the one year period,765 seedling recruits were recorded, of which, 529 tree seedlings (51 species) were identified. The species with the most recruits were Pittosporopsis kerrii (194), Castanopsis echidnocarpa (52), Pseuduvaria indochinensis (48), Parashorea chinensis (48) and Dichapetalum gelonioides (23), which accounted for 69.00% of the total number of identified recruits. The recruitment of the five species with most recruits happened around the conspecific mature trees. In addition, different temporal dynamics of seedling recruitment were found in the five dominant species:the recruitment of Parashorea chinensis and Castanopsis echidnocarpa occurred between early November 2007 February and late October 2008. From late April 2008 to later July, most recruits were presented by Pittosporopsis kerrii and Dichapetalum gelonioides. For Pseuduvaria indochinensis, the recruitment occurred between later July 2008 and later October. |
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