| Qiandao Lake region in Zhejiang Province, China, is an ideal spot to study the secondary succession of forest for it's consistent-formed, well-protected secondary communities. A quadrat (240 m×240 m) was set in Laoshan island of Qiandao Lake Region and the synecological characteristics, population structure and spatial distribution patterns of the dominant tree species and photosynthetic characteristics of seedlings of the dominant species were studied. The main results were shown as follows:(1) The vegetation floristic component analysis shows that there are 91 species in 69 genera and 40 families of vascular plants, among which 3 species in 3 genera and 3 families of pteridophyta,4 species in 4 genera and 3 family of gymnosperms and 84 species in 62 genera and 34 families of angiosperms. There are 77 species in 56 genera and 30 families of dicotyledon and 7 species in 6 genera and 4 families of monocotyledon in the angiosperms. Analysis on the distribution area types of spermatophytes the areal types can be divided into 8 kinds, the tropic type and subtropic type are the most, the temperate type took the second place and the cosmopolitan type was the least. At the genus level, the areal types can be divided into 13 kinds. The tropic type is dominant and there is also quite proportion of temperate type. By the method of Ruankiaer's life-form statistics, phaenerophytes are the dominant species of the community life form. The characters of leaf are mainly microphyllous, simple, coriaceous, unentire. There is a clear distinction between layers, and the vertical structure can be divided into tree layer, shrurb layer and herbaceous layer. (2) The population structure, survivorship curve and spatial distribution patterns of the dominant tree species in this community was analyzed using the method of replacing time series with spatial sequence. The importance values of Pinus massoniana population was the highest (50.47%), followed by Lithocarpus glabra, Castanopsis sclerophylla and Cyclobalanopsis glauca population. The population structure of P. massoniana was spindle type with trend of decline. The number of individuals at 1st and 2nd age size was very small with severe defect in juvenile individuals. The population structures of L. glabra, Ca. sclerophylla and Cy. glauca were pyramid types. Based on the analysis of static life table, the mortality of small size classes was negative, indicating that the P. massoniana seedlings were severely defective and the population of P. massoniana tended to be decline. The survivorship curve of P. massoniana population was a convex curve, while those of L. glabra, Ca. sclerophylla and Cy. glauca populations were approximate linear. The spatial distribution pattern of total individuals or individuals at different size classes of four dominant species presented clumping distribution. In a word, P. massoniana population was stable type with a declining trend, while L. glabra, Ca. sclerophylla and Cy. glauca populations was stable developing. During the succession process, the community would develop into conifer-broadleaved forest and evergreen broadleaved forest at last.(3) The diurnal variations of photosynthetic active radiance, air temperature, air relative humidity, CO2 concentration and the photosynthetic characteristics of seedlings of P.massoniana, L. glabra, Ca. sclerophylla and Cy. glauca in forest gap and understory habitats were studied by using a LCA4 Portable Photosynthesis System in sunny August 2009. In canopy gap, the diurnal change of photosynthetic of P. massoniana was of one-peak type, but the others' were of double-peak type with obvious "midday-depression" of the net photosynthetic rate (Pn), which might be due to the non-stomatal limited elements. In the under-story, all the diurnal photosynthetic variations of seedlings of the dominant species, which were of double-peak type with flat curve. In the canopy gap the daily average Pn of Cy. glauca was significant lower than that of the others, and in the under-story the daily average Pn of P. massoniana was significant lower than that of the others (p< 0.05). There were significant differences of the daily average Pn of P. massoniana, Ca. sclerophylla, L. glabra and Cy. Glauca in different habitats (p<0.05). The LCP,LSP,Amax and Rd of P. massoniana were the highest, those of Ca. sclerophylla took the second place. The LCP,LSP,Amax and Rd of L. glabra, Cy. Glauca were the lowest. AQY of L. glabra, Cy. Glauca were significant higher than P. massoniana and Ca. sclerophylla (p<0.05), with significant differences between P. massoniana and Ca. sclerophylla. Analysis of the chlorophyll fluorescence of seedlings of the dominant species in different regimes, the seedlings of L. glabra, Cy. Glauca suffered photoinhabition in the canopy gap but P. massoniana and Ca. sclerophylla didn't.This indicated that photosynthetic physiological characteristics and material synthesis of seedlings of the dominant species decided the seedlings renew of their population. The renew ability determined their population's status in the community and the mutual competition and change, which could impact the process of community succession significantly. |
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