Study On Seed Rain And Seedlings Dynamic Recruitment In Nonggang Northern Tropical Karst Seasonal Rain Forest

The research of seed rain and seedling recruitment is the key part of understanding forest regeneration mechanism, and forest regeneration is an important matter of biodiversity research and the maintenance mechanism. Studying seed rain and seedling recruitment in the large scale permanent monitoring plots setting up in worldwide, that provide for the biodiversity research and the maintenance mechanism. In this paper,90 seed traps and their associated seedling ptots (270 quadrates of 1m×1m and 180 quadrates of 2mx2m) have been set in the 15 hectare Nonggang Northern Tropical Karst Seasonal Rain Forest Dynamics Plot. From May 2012 to April 2014, the seed traps and seedling plots were investigated regularly, then recording date. Based on the date recorded, we researched the trees’seed rain components, abundance, dynamic variation, spatial pattern, dispersal and the recruitment of tree seedlings, analyzed the correlation between them, and the effect of seed rain and the seedling seasonal dynamic changes on the recruitment of seedlings. The results were as following:(1) A total of 6623 seeds and fruits from 32 trees species belonging to 32 genus and 24 families in the plot were collected in these two years. The seed rain density and species richness were 145.23 ind/mr2 and 0.75sp/m-2, respectively. The species whose seeds were trapped differed over the two years, only four species were continuously recorded, such as Vitex kwangsiensis, Orophea anceps, Cieistanthus sumatmnus and Catunaregam spinosa. The total weight of all the seeds collected was 2025.41 grams, the average weighted 0.31 grams. Mature seeds comprised the major component of seed rain, with the number and weigh of 4321 (65.24%) and 1364.41 grams (67.36%), respectively. There were considerable differences in both the number and weigh of species’seed rain, tree species with large number of seeds and fruits were Canthium dicoccum (3637), Vitex kwangsiensis (1378), Cieistanthus sumatmnus (725) and Garcinia paucinervis (164), all the five accounted for 91.51%; free species with the average heaviest seed rain was Cylindrokelupha robinsonii (7.18 g/m"2), and the lightest was Canthium dicoccum (0.01 g/m-2).(2) There were obvlous seasonal and inter-annual variations of seed rain collected in the two years. For seasonal variation, main time of seed rain centered on the period from June to October, peaking in August firstly and September secondly, appeared bimodal. During May 2012 to April 2013,1124 seeds and fruits were recorded, comparatively,5499 seeds and fruits were collected from May 2013 to April 2014. In the spatial distribution, seed rain in the upper-middle slope was greater than the lower slope and valley bottom, which should be ascribed to the characteristics of fruiting of different communities.(3) We found that seedling in 2012 didn’t change noticeably, neither in species nor in the number of germination or death. But in 2013, many seeds and fruits were produced, part of seed rain germinated without dormancy leading to a big change in quantity and species of seedling. However, hot and humid climate, mainly from May to October, made the quantity of germination greater than of death; but from November to next April when it was cold and dry, there were almost no germination, worse, some seedlings died in this severe environment. All in all, the seed rain and seedling recruitment had an obvious positive correlation in inter-annual.(4) Seeds and fruits of the 32 tree species in the plot achieve to spread mainly by animals, gravity and wind-have 9 species,10 species and 13 species respectively. By analyzing the seed dispersal limitation and recruitment limitation, many species were affected by source limitation, excluding Cieistanthus sumatmnus.Canthium dicoccum, Saraca dives and Vitex kwangsiensis. Most of species were strongly affected by recruitment limitation, but to Cieistanthus sumatmnus.Canthium dicoccum, Sterculia monosperma and Saraca dives, the effect was smaller comparatively.(5) At small scale, the seed rain,seedlings and trees showed a kind of aggregated distribution pattern and they had positive associations. Alternate year bearing were common in this area, under the influence of climate and others, seed rain was collected few and seedlings grew slowly from 2012 to 2013; the time from 2013 to 2014 was a rich year, so many seeds and fruits produced and fell on the floor, then germinating without dormancy, as a result, huge quantity of seedlings emerged and renewed fast. As for forest community types, the different type had the corresponding regeneration dynamic of seed rain and seedling.