Analyses On Regeneration And Succession Of Pine Forests, Formosan Sweetgum Forests In The Southeast Of Hubei Province And Their Seedling Responses To Light And Nitrogen Variation

The middle and lower reaches of Yangtze-river is one of the most important economic districts of China, which also is recognised as an ecologically degraded and frail area that needs to be restored and conserved. Pine (Pinus massoniana) forest and Formosan swwetgun (Liquidambar formosana) forest are the most important forest of this district. To manage these vegetation effectively, a full understanding of their natural succession was essential. In this paper, a series of field work and control experiments in green house was conducted to study the regeneration and succession of these two forest types. The results indicated that:(1)in Pine forests, the population of P. massonaina was a cohort aged from 25 to 30 years, but the population of Formosan sweetgum was as an increasing population; on the other hand, the Formosan sweetgum population in sweetgum forests was a decreasing population; the shoot growth of Platycarya strobilacea and Albizia julibrissin seedlings decreased earlier than pine and Formosan sweetgum. (2) Seedling regeneration and sprout regeneration were coexisted in sweetgum populations. Higher survival of stumps, higher "self-thinning" of existing sprouts and higher shoot growth rate than seedlings are the characteristics of Formasan sweetgum sprouting. (3) Our experiments suggested that non-dormant seed and seedling shade intolerance were the key factors limiting seedling regeneration of L. formosana. We did not find any litter leachate inhibition effect on seed germination and store. (4)Survival, growth, and morphology of Quercus acutissima, Quercus serrata var. brevipetiolata, L. formasana, P. massoniana, P. strobilacea seedlings were strongly affected by PAR (Photosynthetic active radiation), but nitrogen supply had little effects on these traits. The shade tolerance rank among five species was Quercus acutissima> Quercus serrata var. brevipetiolata>L. formasana>P. massoniana>Platycarya strobilacea. Our results also suggested that there was no RGR (Relative growth rate) rank reversal among PAR gradients. The effects of PAR on seedlings functional traits conferring to RGR were different between Q.acutissima, Q. serrata var. brevipetiolata and shade intolerant species L. formasana, P. massonian and P. strobilacea. Shade tolerant species had a higher RMR, but shade intolerant species showed a higher LMR (Leaf mass ratio), LAR (Leaf area ratio), and SLA (Specific leaf area). According to the data that shade tolerant species possessed a lower mass based Amax (Light-saturated CO2 assimilation rate), mass based Rd (Dark respiration rate) and the results of whole plant gas exchange simulation, we concluded that strategies of shade tolerant species under low light environment were low leaf investment, low carbon capture rate and low respiration rate. Our results also revealed that seedling survival was strongly correlated with the NSC (Non-structural carbon) concentration in root.