Seed Germination, Seedling Emergence And Early Seedling Establishment Of Micro-landform Dominant Tree Species On Various Micro-landform Units In Tiantong National Park, Zhejiang

Seed germination, seedling emergence and seedling establishment as early stages of forest regeneration are critical in the formation and development of vegetation patterns. Topographical structures induce environmental factors'differences, which determine the seedling establishment and consequent tree growth. Studies on seedling dynamics in various topographical positions are important to explain the role of seedling establishment stage in the formation of vegetation patterns and be critical for understanding small-scale vegetation pattern and regeneration of degraded forests. Based on former vegetation investigations,7 micro-landform dominant tree species were selected, and through indoor seed germination experiment, outdoor direct seeding and seedling monitoring we investigated seed germination, seedling emergence and seedling establishment on various micro-landform units. The role of seedling establishment stage for the formation of present vegetation pattern was discussed, results are:(1) Indoor experiment indicated that 7 kinds of seeds were either dormant or had low continuous germination rates. Water contents of Cyclobalanopsis nubium and Lithocarpus harlandii, Castanopsis fargesii and Choerospondias axiliaris were higher than 30%; water contents of Carpinus viminea, Schima superba and Celtis vandervoetiana were between 10%～20%. Germination rates of Carpinus viminea and Choerospondias axiliaris were 0, and others were lower than 60%. Cyclobalanopsis nubium had the highest germination rate (56.50±7.14%) while Castanopsis fargesii the lowest(6.00±1.42%).(2) There was no significant difference among the micro-landform units and light conditions (p<0.01). Total gap fraction on the upper slope was larger than that of lower slope. Total gap fraction had a trend of increasing with the increase of altitude. Soil erosions were not significantly related with micro-landform units and light conditions (p>0.05).Soil moistures were significantly different among micro-landform units (p<0.001), and not significant between light conditions (p=0.067). Soil moisture was obviously higher than that of lower slope. In each month there was a trend that soil moisture on upper slope was higher than that of lower slope.(3) 7 kinds of seeds had different germination strategies. Carpinus viminea and Schima superba of group A geminated the first, Choerospondias axiliaris and Celtis vandervoetiana of group B the second, and Castanopsis fargesii, Cyclobalanopsis nubium and Lithocarpus harlandii of group A the latest. Schima superba, Carpinus viminea and Celtis vandervoetiana had the largest seedling numbers in April, and had high mortality rates. Choerospondias axiliaris had the largest number in May and June among the micro-landform units and had relatively low mortality rate. Castanopsis fargesii, Cyclobalanopsis nubium and Lithocarpus harlandii reached the largest amounts at the end of the 1st growing season and had high survival rate. (4) Seedling emergence rate was influenced by one or a number of environmental factors, and was not significantly different among the micro-landform units. Seedling emergence was at least correlated with one of the environmental factors, namely soil moisture, total gap fraction and soil erosion, except for Lithocarpus harlandii and Celtis vandervoetiana. Seedling emergence was not significantly different between the light conditions (except for Choerospondias axiliaris on lower hillslope area, P<0.001) and slopes (except for Choerospondias axiliaris under canopy,P=0.048). Seedling emergences of Carpinus viminea and Castanopsis fargesii were not significantly different among the micro-landform units. Seedling emergences of Schima superba, Cyclobalanopsis nubium, Lithocarpus harlandii, Choerospondias axiliaris, and Celtis vandervoetiana had little differences except for some micro-landform units, which indicated that seedling emergences at a micro-landform unit scale were not significantly different.(5) Seedling survival rates and seedling mortality rates varied among species, and were affected by environmental and biological factors. Seedling survival rates of Castanopsis fargesii, Cyclobalanopsis nubium and Lithocarpus harlandii were obviously higher than other species and seedling survival rates of Castanopsis fargesii and Lithocarpus harlandii at some micro-landform units could reach 100%. Carpinus viminea had relatively lower seedling survival rate. Seedling survival rates of all tree seedlings except for Carpinus viminea decreased with the increase of soil moisture. The increase of total gap fraction significantly increased the seedling survival rates of Carpinus viminea, Schima superba, Castanopsis fargesii and Cyclobalanopsis nubium. Seedling survival rates of Carpinus viminea, Schima superba, and Cyclobalanopsis nubium decreased with the increase of soil. Withering was the main cause of mortality of Carpinus viminea, Schima superba and Choerospondias axiliaris. The main cause of Cyclobalanopsis nubium and Lithocarpus harlandii was physical damage.(6) Seedling establishments varied not significantly among the micro-landform units, except for some units which were not correlated with the pattern of the adult trees. These results do not fit the former observed vegetation pattern on various micro-landforms. Seed germination, seedling emergence and seedling establishment of the studied species are the results of the synthesis of seed biological characteristics and environmental factors'influences, and these stages are not the main cause of the present vegetation pattern among the micro-landform units in Tiantong area. The present vegetation distribution differences are likely to vary among the dispersal, sapling, small tree or even big tree stage, which may be related with their different adaptabilities to soil and climate or other factors.