| The large-scale rubber cultivation in the countries of Lancang-Mekong region has a certain impact on the ecosystem of tropical regions.At present,the effect of rubber planting on plant diversity in this area has not been studied comprehensively.The objective of this study was to analyze the composition of species and diversity of understory,rubber plantations in Lancang-Mekong region.Using typical sampling and random sampling methods,240 samples with an area of 100 m~2(10 m×10 m)were selected in 6 countries including Vietnam,Cambodia,Laos,Thailand,Myanmar and China.We comprehensively investigated the composition,abundance and coverage of plants in the plot,and analyzed the composition,distribution characteristics and uses of plant species in the community,as well as the diversity and influencing factors of plant species under different angles.The main results of this study were as follows:(1)There were 153 families,550 genera,and 949 species of plants in the rubber plantation on the Lancang-Mekong region,including 76 species of ferns,3 species of gymnosperms and 870 species of angiosperms.Among them,there were 86 families,278genera and 445 species of herbaceous plants.There were 32 families,62 genera and 101species of liana.There were 42 families,118 genera and 192 species of shrubs.There were66 families,151 genera and 211 species of tree.The undergrowth of rubber community was dominated by herbaceous plants(46.89%).The dominant families mainly include 318species of 163 genera in 9 families including Butterfly,Euphorbia,Gramineae,Rubiaceae,Compositae,Liliaceae,Mulberry,Sedge and Araceae,the number of species accounted for33.72%of the total species,which had obvious advantages.The dominant genera include46 species in 4 genera,such as Ficus,Solanum,Dioscorea and Smilax.The dominant species mainly include Cyrtococcum patens,Eupatorium odoratum,Asystasia chelonoides,Axonopus compressus and Ficus hispida.In the Lancang-Mekong region,most of species under the rubber plantations have utilization value,including 597 species of medicinal plants,163 species of edible plants,220 species of economic plants,64 species of forage plants,158 species of ornamental plants,62 species of ecological plants and 170 species of unidentified uses.(2)There were 128 families,512 genera and 873 species of seed plants in the rubber plantations in Lancang-Mekong region,and the tropical distribution of families and genera had the largest proportion,with 84 families and 475 species of tropical distribution family and 428 genera and 732 species of tropical distribution genera.The ratio(R/T value)of the tropical and temperate components of seed plant families and genera in communities was 10.5 and 8.09,respectively,and the tropical properties of seed plant families and genera were obvious.Comparing with the geographical components of seed plants of rubber plantations in 6 countries in the Lancang-Mekong region,it showed that the ratio of tropical components to temperate components of the seed plants in 6 countries(R/T value),was Cambodia(64.00)>Vietnam(28.00)>Myanmar(26.20)>Thailand(17.82)>China(17.50)>Laos(7.77),in addition,the tropical characteristics were obvious in 6countries.Six countries had the absolute advantage in the world wide distribution and tropical distribution,with the tropical distribution accounting for more than 50%of the family.(3)The variation patterns of the richness index,Shannon-Wiener index and Simpson index of the 6 countries in the Lancang-Mekong region were,Laos>Myanmar>China>Cambodia>Thailand>Vietnam of which the biodiversity of Laos was significantly higher than that of other countries,Vietnam had the lowest biodiversity.The plant species diversity of the rubber plantations community in the Lancang-Mekong region increased with the increase of forest age,with the highest diversity of rubber plantations with the age of>30 years and the forest age<8 years had the lowest species diversity.Species diversity in rubber undergrowth was different at different elevations(<200 m,200 m to 500 m,500m to 700 m,>700 m).Both the richness index and the Shannon-Wiener index were high between 500~700 m,while the richness index and the Shannon-Wiener index were lowest between 200~500 m and the Simpson index were the lowest in the range of<200 m.Under the conditions of different slopes(<2°,2°to 15°,15°to 25°,>25°),the species diversity of rubber plantations community shows an upward trend with the increasing slope under the different slopes(<2°,2°to 15°,15°to 25°,>25°),with shope<2°being the lowest and slope>25°being the highest.With the increase of latitude,the species diversity of showed an upward trend,while the species diversity showed a downward trend with the increase of longitude.The total species diversity index showed an upward trend with the increase of canopy density,and the richness index and Shannon-Wiener index were the highest between 80%and 90%of canopy density.With the increase of temperature and precipitation,the species diversity index showed an increasing trend,but the rate of increase was slow and the fitting degree was low.(4)Through the similarity analysis of rubber forest communities in the Lancang-Mekong region of Vietnam,Cambodia,Laos,Thailand,Myanmar and China,the overall variation range was 0.29 to 0.47,which reflected the similarity of species composition under rubber plantations in 6 countries.The high similarity between Myanmar and Thailand was 0.47,while the low similarity between China and Cambodia and Myanmar was 0.29,respectively,which was largely influenced by geographical environment factors and the location factors of rubber plantations.(5)The relationship between the distribution of plant species of rubber forests and10 influencing factors such as temperature,altitude,rainfall,latitude and longitude,gradient,slope direction,age,crown density and higher was studied in Lancang-Mekong region rubber plantations,the result showed that the relationship between the influencing factors of 10 influencing factors on the distribution of species accounted for 9.41%,the temperature explained the biggest contribution(1.14%),followed by latitude accounted for1.05%.Through analysis,it was found that the explanatory quantities of the 10 influencing factors were relatively low on the distribution of each species,indicating that the interference of human factors had a greater impact on the distribution of species.Temperature is the biggest factor in the distribution of species,followed by latitude and longitude.Temperature is influenced by longitude,latitude,altitude and so on,and also affects the distribution of species.(6)There were 45 families,91 genera and 121 species of exotic plants under the rubber plantations in the Lancang-Mekong region,accounting for 12.75%of the total species.Among them,the majority of the plants are herbaceous,with the largest number of Compositae and 237 sample lands containing invasive plants,most of which were from tropical America.The most invasive plants were found in Thailand(60 species),and the highest proportion was found in Cambodia(17.86%).There were 9 samples of more than10 species of invasive plants.With the increase of invasive plants richness,the richness index of the sample increased. |
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