Study On The Suitability Of Main Invasive Plants In Hainan And The Influencing Factors Of Their Population Dynamics

Invasive plants have always been concerned by the ecological scientists,but the dynamic changes after the invasion of invasive plants,we need to do in-depth research.In this paper,the distributions of six invasive plants will be predicted by MaxEnt and ArcGIS technology,combined with field survey data on Hainan Island.The six invasive plants are Mimosa pudica,Chromolaena odorata,Lantana camara,Praxelis clematidea,Wedelia trilobata,and Conyza sumatrensis.The distributions characteristics and change trends of these invasive plants were used fixed-point tracking to monitor in different habitats(cultivated land,woodland,grassland,shrub)on the north-west of Hainan to test the results of above predictions.The main results were as follow:(1)The suitable establishment areas of the six invasive plants are gradually decreasing from coastal to inland.The climate,elevation,aspect,temperature,rainfall and land use type are impact factors for distributios of invasive plants.Further analysis using the Jackknife showed that land use type is an extremely important factors.There are high suitability of these invasive plants in the surrounding areas of villages,urban construction land,other construction land(mines),and cultivated land.The distribution fit levels of these invasive plants are different in different types of woodland and grassland.The suitability of these invasive plants is higher in shrubbery,sparse woodland,and other woodland habitats than in woodland(natural forest and plantation with canopy density>30%).The suitability is higher in low-coverage grassland and medium-coverage grassland habitats than in high-coverage grassland(>50%).(2)The 75 plots were surveyed in northwest regionthe of Hianan island,in order to study the distribution characteristics of invasive plants.The results showed that frequency of six invasive plants was Chromolaena odorata(84.8%)>Mimosa pudica(39.1%)>Praxelis clematidea(20.9%)>Lantana camara(18.7%)>Wedelia trilobata(14.1%)>Conyza sumatrensis(6.7%).The coverage of these plants was Chromolaena odorata(32.4%)>Wedelia trilobata(7.7%)>Mimosa Pudica(5.9%)>Lantana camara(5.9%)>Praxelis clematidea(3%)>Conyza sumatrensis(0.79%).The density of these plants was Chromolaena odorata(2.19 strain/m2)>Mimosa pudica(1.91 strain/m2)>Wedelia Trilobata(1.83 strain/m2)>Praxelis clematidea(0.8 strain/m2)>Conyza sumatrensis(0.22 strain/m2)>Lautana camara(0.09 strain/m2).The frequency,coverage,and density of these plants were cultivated land>grassland>shrub>woodland.The results of fixed-point tracking monitoring indicated that the frequency,coverage,and density of invasive plants were changed greatly by the changes of land use and species competitions.We can see that the frequency,coverage,and density of these invasive plants declined.After 4 years,the frequency of six invasive plants was Chromolaena odorata(20.5%)>Praxelis clematidea(12%)>Mimosa pudica(9.3%)>Lantana camara(6.7%)>Wediola trilobata(6.7%)>Conyza sumatrensis(0%);the coverage was Chromolaena odorata(4.8%)>Wediola trilobata(3.9%)>Mimosa pudica(3.2%)>Lantana camara(1.3%)>Praxelis clematidea(1.2%)>Conyza sumatrensis(0%);the density was Wedelia trilobata(1.1 strain/m2)>Chromolaena odorata(0.6 strain/m2)>Mimosa pudica(0.52 strain/m2)>Praxelis clematidea(0.43 strain/m2)>Lantana camara(0.08 strain/m2)>Conyza sumatrensis(0 strain/m2).The average frequency of these invasive plants were from 28.9%to 1.12%,32.7%to 10.9%,27.8%to 5.6%,and 28.5%to 13.9%;the average coverage were from 13.7%to 0.47%,11.5%to 1.04%,6%to 0,61%,and 4.6%to0.25%;the average density were from 1.9 strain/m2 to 0.24 strain/m2,1.62 strain/m2 to 0.726 strain/m2,0.9 strain/m2 to 0.5 strain/m2,0.32 strain/m2 to 0.055 strain/m2,on the cultivated land,the grassland,the shrub,and the woodland between in the first and last survey.This change was related to different habitat types.The results showed that the more instability of the land ecosystem,the greater the change.(3)The results also showed that the land use change was the main factors for affecting the distribution change of these invasive plant.There were 45 plots that disappeared within 4 years,accounting for 60%.Of the 45 disappeared plots,38 plots were disappeared due to land use changes,accounting for 84.4%,and 7 were disappeared due to competition with other plants,accounting for 15.6%.We can see that the cultivated land and grassland are easier to change than woodland and shrub.The change of Conyza sumatrensis was mainly affected by competition with other plants,the change of other invasive plant species was mainly affected by land use change.(4)The results showed that invasive plants were never seen due to natural competition in 7 plots,due to land use change in 38 plots.There were 30 plots remain basically.Monitoring data analysis of these 30 plots showed that the frequency and coverage of Chromolaena odorata,Mimosa pudica,Lantana camara and Conyza sumatrensis had slowly decreasing trend,Praxelis clematidea and Wedelia trilobata had slowly increasing trend;the changes of density of these invasive plants had a slowly increasing trend except Conyza sumatrensis that were never seen on the plots from 2014.These changes are not obvious,still need further observation.These results of studies indicate that invasive plants are more likely to invade secondary environments that are disturbed by humans.However,the population characteristic of these invasive plants would change by land use change after the invasion.Most of the plots disappeared due to changes of land use,and some disappeared due to competition with other plants.Chromolaena odorata has the strongest adaptability,followed by Wedelia trilobata and Mimosa pudica,again with Praxelis clematidea and Lantana camara,and finally Conyza sumatrensis.The invadability of land for these invasive plants is arable land>grassland>shrub>woodland,and the retentivity of land for these invasive plants is arable land<grassland<shrub<woodland.