| Pollen analysis has proven to be an effective way to interpret and reconstruct past vegetation patterns and to effectively try to understand the likely effects of future environmental changes.Relative pollen productivity(RPP)refers to the ratio of the amount of pollen produced by the corresponding plant species of a certain type in a unit projected area to the amount of pollen produced by the corresponding plant species in the same area of the reference plant species(RPP = 1).The Relevant source area of pollen(RSAP)represents that the correlation between the pollen deposited at a site and the surrounding vegetation exceeds a certain distance,but the correlation does not improve.In other words,with the expansion of the radius of the sedimentary basin,the accumulation of certain type of pollen does not change.RPP and RSAP are necessary data for Landscape Reconstruction Algorithm(LRA)to reconstruct regional palaeo-vegetation.Tianmu Mountain area has typical subtropical forest vegetation landscape.The study of RPP and RSAP in this region(118°39?08.54?-119°53?0.55?E,29°51?36.28?-30°50?18.45?N,24-497 ma.s.l)is of great significance for understanding the relationship between pollen and vegetation in the subtropical forest region,as well as the quantitative reconstruction of the past land cover in the subtropical region by using fossil pollen.Based on the pollen and vegetation data of 33 sample sites in Tianmu Mountain,this study estimated the relative pollen yields of 12 major pollen types and determined the RSAP of deciduous and broad-leaved mixed forest in Tianmu Mountain by using the Extended R Value Model(ERV)model and the vegetation pollen data of 25 sample sites.To verify the reliability of RPP,using the Landscape Reconstruction Algorithm,REVEALS(Regional Estimates of VEgetation Abundance from Large Sites)model and Love(Local Vegetation Estimate)model,were used to quantitatively reconstruct the Vegetation coverage of the other 8 sample points.By comparing the Vegetation coverage with the actual survey,it was confirmed that the landscape reconstruction method was also applicable in this study area.The results are as follows:(1)There are 39863 pollen grains were identified from 33 sample sites in Tianmu Mountain,belonging to 54 pollen types of arbor plants,17 pollen types of shrub plants,41 pollen types of herbaceous plants and 2 spore types of pteridophytes,belonging to 114 families and genera.The 12 pollen types selected in this paper are: Pinus,Quercus(a deciduous species of the genus Quercus),Artemisia,Moraceae,Poaceae,Liquidambar,Mallotus,Cyclobalanopsis,Cyperaceae,Rosaceae,Theaceae,Taxodiaceae.The settling rates of 12 selected pollen types were calculated,and the results showed that the pollen of Pinus had the highest settling rate(0.150 m/s),the pollen deposition rate of Cyclobalanopsis was the lowest(0.005 m/s).(2)323 species belonging to 101 families were identified by field vegetation investigation,the vegetation composition is mainly composed of arbor group and herb group.According to the composition of vegetation species,seven main community types can be divided: coniferous forest(4),evergreen broad-leaf forest(2),broadleaved deciduous forest(2),mixed coniferous broad leaved forest(15),evergreen-deciduous broad-leaved mixed forest(3),phyllostachys forest(3),Theaceae plant association(2),carya cathayensis forest(2).(3)The combination of Prentice weighting method and ERV sub-model 3 has the highest likelihood function score and the best data fitting degree,and relevant source area of pollen on evergreen and deciduous broad-leaved mixed forest in Tianmu Mountain is about 290 meter.(4)Taking Quercus(a deciduous species of the genus Quercus)as the reference species(relative pollen yield was 1),the relative pollen yield of 12 major plant genera in Tianmu Mountain was obtained,and the RPP sequence was as follows: Pinus(14.922±1.337)>Artemisia(1.325±0.119)> Quercus(a deciduous species of the genus Quercus)(1)> Moraceae(0.677±0.447)> Poaceae(0.619±0.039)> Liquidambar(0.581±0.069)> Mallotus(0.435±0.054)> Cyclobalanopsis(0.130±0.057)> Cyperaceae(0.097±0.023)> Rosaceae(0.073±0.016)>Theaceae(0.062±0.004)>Taxodiaceae(0.035±0.028).Cyclobalanopsis and Theaceae were first estimated all over the world.The RPP of the same pollen type is different in different study areas,which may be related to the different plants corresponding to the same pollen type.The RPP of Pinus is obviously higher than that of other subtropical regions,which may be due to the different vegetation types of Pinus in different altitudes.The RPP of Artemisia was significantly higher than that of Dabie Mountain,but lower than that of Shandong,which might be related to the higher proportion of farmland and the distribution of bamboo forest communities.In addition,the selection of reference species,palynological transmission mode,flowering period of plants,climatic topography,sample types and sampling methods may also cause differences in pollen yield.(5)By comparing the reconstructed vegetation coverage with the actual vegetation coverage using the landscape reconstruction algorithm(LRA),a scatter plot was made and the correlation coefficient was calculated.The results showed that the reconstructed relative vegetation coverage had a strong correlation with the investigated vegetation coverage.Among the tree types,the reconstructed coverage of Pinus was higher than the surveyed coverage,with the best correlation(correlation coefficient was 0.95).The reconstructed coverage of Deciduous Quercus,Taxodiaceae,Liquidambar,and Moraceae had a higher fitting degree with the actual coverage(correlation coefficient > 0.82).The results showed that the RPP and RSAP results of the main plant types obtained in this study were reliable and could be applied to the quantitative reconstruction of the palaeo-vegetation in the evergreen and deciduous broad-leaved mixed forest in the Tianmu Mountain area.This paper selected Tianmu Mountain area for pollen collection and vegetation survey,estimated RSAP and RPP,and reconstructed regional vegetation at the same time.On the one hand,it provided research on pollen production in different regions,and explored the reasons for the differences in pollen production in the study area of evergreen and deciduous broadleaved mixed forest at different altitudes in the subtropical monsoon area.On the other hand,the applicability of the landscape reconstruction algorithm in subtropical zone is further verified. |
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