| Ambrosia artemisiifolia L.and Ambrosia atrifida L.are serious annual malignant invasive weeds worldwide.Since their invasion in the Yili River Valley was confirmed in 2010,the distribution area of the two invasive species has increased by 10,150 times and 2,150 times respectively from 2016,seriously endangering the local ecological environment and the development of the tourism industry,and having the risk of spreading throughout Xinjiang.Therefore,it is necessary to study the spatial distribution pattern and community species diversity characteristics of the two species,summarize the invasion and diffusion rules of the two species,and take effective measures to prevent and control them efficiently.Through the general survey of the whole Yili River Valley,this thesis records the data of the distribution area and distribution area of the two species,analyzes and summarizes their spatial distribution characteristics and habitat preference;With the help of geostatistics,the diffusion routes and transmission media of the two species in six habitats such as both sides of the road,grassland,farmland,under the forest and river were analyzed;By analyzing the species diversity composition and niche characteristics of associated species in the invasive community,the community characteristics that the two species can invade are proved.The results are as follows:1.The distribution of A artemisiifolia and A atrifida has obvious habitat preference,mainly distributed on both sides of roads,under forest,river habitat and meadow.Among them,there are 186 A artemisiifolia distribution populations in total,of which the largest populations are distributed on both sides of the roads,accounting for 32.34%of the total distribution populations,followed by 22.84%under forest and 14.98%on farmland.Relatively few distribution points were recorded in residential areas,river courses and grassland habitats,accounting for 8.82%,9.27%,and 11.75%,respectively.Many habitats on both sides of the river are continuously distributed in strips,and the population distribution area is the largest,accounting for 69.01%of the total distribution area of the Yili River Valley.A total of 138 A atrifida populations were recorded,mainly in the grassland,under the forest and on both sides of the subgrade.The largest population points are distributed in the grassland habitat,accounting for 26.09%of the total distribution points,and its distribution area is also the largest,accounting for 72.79%of the total distribution area of Yili River Valley.In general,A artemisiifolia has a wider distribution range and larger distribution area than A atrifida.2.The study on the spatial distribution pattern shows that the invasion area of the two species is mainly in Xinyuan County.The A artemisiifolia population has formed 4 serious invasion areas and multiple diffusion source areas(mainly located in Zeketai Town,71 Regiment,Bestobe Township;Turgen Township and Alemale Town;Arele Tobe Township,Kansu Town,and the western area of Nalati Town;and the 1st Company of the 79th Regiment and the surrounding area of the Agricultural Village),the invasion areas of the severely invaded areas reached 6.53 km~2,16.68 km~2,27.91 km~2 and 5.37 km~2,respectively.The A atrifida population has formed two serious invasion areas and dense multiple diffusion source areas.The serious invasion areas are mainly located in the east of Zeketai Town,Turgen Township and part of the 71st regiment and the 79th regiment and the agricultural In the surrounding area of the village,the distribution area of severe invasion area is 12.02 km~2 and 1.01 km~2.Severe intrusion zones contain diffusion source zones.3.According to the size of the A artemisiifolia population,six different invasion periods were artificially divided.The geostatistical study found that the population with the largest distribution area(initial invasion stage)was randomly distributed in the distribution area,indicating that A artemisiifolia initially invaded the local area through random factors.The two species showed a concentrated distribution in six habitats including road sides,pastures,farmland edges,forests and river channels.Combining visits and field investigations,it is found that the dispersal vectors of different habitats have their own emphasis.Among them,the distribution in the habitats on both sides of the roads,pastures and farmland mainly depends on cattle and sheep activities and transfer,transportation of agricultural and animal husbandry materials,and transportation of agricultural machinery.In forests and residential areas,it mainly depends on animal activities and the transportation of agricultural and animal husbandry materials;in rivers and canals,it mainly depends on water flow and animal activities.4.In terms of species composition of the invasive community,there are 21 families and 60 planting species in the A artemisiifolia invasive community,including 16 species of Gramineae,13 species of Compositae,4 species of Leguminous and Polygonaceae plants each,accounting for 55%of the total species.The percentages of Gramineae and Compositae species in quadrats were 93.5%and 89.7%respectively.According to the statistics of A atrifida invasive community,there are 18 families and 38 planting species,including 9 species of Gramineae and 9 species of Compositae.The percentages of Gramineae and Compositae species were 91.3%and 77.5%respectively.Artemisia caruifolia,Erigeron canadensis,Achillea millefolium,Setaria viridis,Eleusine indica and Elymus dahuricus are the main dominant species in the invasive community of A artemisiifolia and A atrifida.The correlation analysis between the coverage of A artemisiifolia and A atrifida invasion quadrat and the richness of associated species found that the invasive ability of the two species was not related to the species richness of the community.5.The analysis of species niche characteristics showed that A artemisiifolia and A atrifida have the largest niche width in each invasive habitat,and the niche width ranged from 0.983 to 0.996.The overlap coefficients between the two species and the associated species in the invasive area are between 0.808-0.996and 0.615-0.998 respectively,which are highly overlapped with the local associated species in resource utilization.Therefore,there is a high-intensity competitive relationship between the two species.To sum up,A artemisiifolia and A atrifida have obvious habitat preference,which are mainly distributed on both sides of the road,under the forest,beside the farmland,grassland and river habitat.The initial invasion of the two species is random diffusion and once settled successfully,the bridgehead strategy will be used to expand the population nearby.A artemisiifolia and A atrifida have obvious habitat preference,which are mainly distributed on both sides of the roads,under the forest,beside the farmland,meadow and in the river habitat.Livestock activities such as cattle and sheep,transportation of agricultural and animal husbandry materials,farming machinery,roads,and water flow are mainly the transmission media for the long-distance diffusion of the two species.This paper provides basic data for the study of diffusion distribution and community characteristics of A artemisiifolia and A atrifida in Xinjiang. |
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