| Soil seed bank and seed rain provide the plants with settlement, survival, reproduction and development, and both of them play an important role in regenerating and recovering vegetation during the succession of community. For years, the lack of systematic research on the base of biological material and the rule of bioecology had made the natural recovery achieved little in the natural secondary broad-leavd forest on the western margin of Sichuan basin. This paper adopts the time series instead of spatial series to explain the evolvement and community development direction of the broadleaved natural recovery in this area forest through doing research on the structure, diversity, relativity, spatial distribution pattern about natural secondary broad-leaved forest at different time. Using the self-recovery of ecological system aims to provide theoretical and practical thesis for recovering and reconstructing the degenerating forest ecosystem in similar background. According to the shade tolerance, life form and structure, the present situation of vegetation recovery period was divided into three periods, including the prophase stage, the prometaphase stage and the metaphase stage. Through researching on the vegetation plot and the simple investigation of soil, the studied conclusions were as follows:1 The species proportion of soil seed bank was different at different recovery phases. The researched area belongs to subtropical evergreen and deciduous broad-leaved mixed forest. The species of soil seed bank at the three phases had 15 families and 23 species which consist of 4 herbs,8 shrubs and 11 arbors. Arbors and shrubs are mainly deciduous species. Herbs are mainly Balsaminaceae family and Poaceae family. Shrubs are mainly Rosaceae and Saxifragaceae. Arbors are mainly Cornaceae family and Rosaceae family. With the succession, the soil seed bank decreases gradually and the arbor, shrub, and herb decrease at the same time. The percent of herb seed increases first and the decreases late, and the maximum appears at the prometaphase stage, which is up to 20.29%, and the minimum is 9.18% at the metaphase stage. The shrub decreases first and the increases late, and the maximum appears at the metaphase stage, which is up to 15.31%, while the minimum is 5.72% at the prometaphase stage. The arbor increases all the time and the maximum is up to 75.51% at the metaphase stage.2 The storage of soil seed bank was different at the different recovery phases. The maximum of soil seed bank is 1610.29 ind.m-2 at the prophase stage, and the second is 610.42 ind.m-2 at the prometaphase stage, and the minimum is only 293.75 ind.m-2 at the metaphase stage. The difference is affected by the forest age and the amount of fruits. According to the activity of seeds, the highest percent is 55.28% at the prophase stage. The next one is 54.97% at the metaphase stage. The lowest one is 53.03% at the prometaphase stage.3 The species diversity of soil seed bank was different at three recovery phases. According to the data of the whole year, the conclusions were showed that with the succession, and Pielou index increases gradually and its change interval was from 0.672 to 0.785, and Marglef index and Shannon-wiener index decrease gradually and the former change interval is from 1.4146 to 1.82 and the latter is from 2.0716 to 2.0773, and Simpson index increases gradually and its change interval is from 0.8038 to 0.8149.4 The vertical distribution of soil seed bank was obvious in small-scale space. The number of species decreases with the soil depth increasing. The number of seeds increases first and decreases late with the depth increasing. With the succession, Pielou index of the litter layer decrease gradually and its change interval is from 0.813 to 0.878, and them of other three layers increase gradually and its change interval is from 0.64 to 0.932. The Marglef index decreases all the time and its change interval is from 0.5378 to 1.7421. The change interval of Shannon-wiener index is from 1.5794 to 1.8132. The change interval of Simpson index is from 0.7118 to 0.8205. The percent of seeds at the litter layer increases gradually. The density ratio of seeds decreases gradually when the soil layer is from 0cm to 5cm and from 5cm to 10cm and the change interval is from 3.09 to 4.14. That data show that it can benefit seed storage increasing soil depth.5 The characteristics of forest seed rain were different with different recovery phases. The species and the amount of seed rain decrease. The seed survival rate increases first and decreases late. The seeds are equally distributed. The Marglef index decreases gradually. The Shannon-wiener index and the Simpson index increase first and decrease late. The species of seed rain collected in the whole year consists of 9 families and 15 species which consist of 5 shrubs and 10 arbors. At the prophase stage, the species of seed rain consists of 9 families and 13 species which consist of arbors mainly, and the rainfall of seed has reached to 55.97 ind.m-2, and the survival rate increases first and decreases late, and the highest rate is 98.44% in October. At the prometaphase stage, the species of seed rain consists of 8 families and 10 species which consist of shrubs mainly, and the rainfall of seed is up to 16.83 ind.m-2, and the seed survival rate waves, and the highest rate is 99.49% in September. At the metaphase stage, the species of seed rain consists of 6 families and 7 species which consist of arbors mainly, and the rainfall of seed is up to 11.80 ind.m-2, and the seed survival rate increases with the whole year and the highest survival rate appears in October and November.6 The similarity indexes were different in the natural secondary broad-leaved forest at different recovery phases. The similarity index between the soil seed bank and the vegetation and between the soil seed bank and the seed rain increase first and decrease late with the succession, and the maximum index appears at the prometaphase stage, and the Sorensen index is 0.71 and 0.55 respectively. The similarity index between the seed bank and the seedling decreases first and increases late, and the minimum is 0.17 which appears at the prometaphase. At all the recovery phase, there were many seedlings which consist of mainly shrubs. The soil seed bank can provide the basis for the natural recovery ability and the biodiversity in secondary broad-leaved forest on the western margin of Sichuan basin.7 Many relativity indexs of soil seed bank were negative correlation at different recovery phases. Through X2 statistics test and relativity index AC,231 pairs of species of seeds were researched in August at three periods.At the prophase stage, the relativity were positive correlation in the 25 of the 66 pairs of seed species, and negative correlation in the 41 of the 66 pairs of seed species. At the prometaphase stage, the relativity were positive correlation in the 32 of the 120 pairs of seed species, and negative correlation in the 86 of the 120 pairs of seed species,and two of the 120 pairs are independent totally (Cornus controversa Hemsl-Sorbus wilsoniana Schneid, Cornus controversa Hemsl-Swida macrophylla Wall). At the metaphase stage, the relativity were positive correlation in the 17 of the 45 pairs of seed species, and negative correlation in the 28 of the 45 pairs of seed species. At this stage, there being none distinct species shows that the ecological community is relatively stable. Most of the species pairs were negative correlation which ntensity is higher, and it can be forecasted that competition of interspecies and species replacement would be fierce and frequent and the forest structure was not stable. In the process of operation and management, it should be adopt the measures that were thinning for easing contradiction, reduce self-thinning phenomenon due to competition.8 The soil seed bank presents a polymerizability distribution in small-scale space at different recovery phases. However, the degree of polymerizability was different. Take the PAI, Polymerizability Index, as an example; the indexes were 1.89 at the prophase stage, 1.97 at the prometaphase stage and 1.32 at metaphase stage. The example showed that the distribution of soil seed bank tends to be random in small-scale space. |
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