Study On Diffusion Mechanism Model Of Invasive Exotic Plants

With the globalization trend of development, exotic species invasion has become an integral part of the global environmental change. Every year due to invasive exotic species cause enormous economic losses, and increasing activities of exotic species invasion, some parts of China has caused enormous ecological imbalance and economic losses. The Qinghai-Tibet Plateau is the world's most ecologically fragile areas, the Qinghai-Tibet Railway allows this area more frequent contact with the outside world, the vegetation along the railway has had a certain impact. Through the establishment of the mechanism model spatial diffusion of alien plants, analysis of the impact of invasive species spread factors, while a typical simulate the typical invasive species along the Qinghai-Tibet Railway diffusion. it has great significance of invasive exotic species prevention and control, while the vegetation on the Qinghai-Tibet railway rehabilitation and reconstruction, to prevent exotic species invasion was a certain practical significance.This CA model for intrusion theory and combined with the initial CA model of neutral landscape model, competition model of seed, seed propagation model and adult competition model, the formation of CA model for the spread of plant invasions. The model can be set to the extent of different habitats intact degree, life history parameters of different plants, different competitive ability and outline the different distribution patterns of plants, through the diffusion process of dynamic simulation of invasive exotic species, output the landscape patterns and the occupied habitat conditions of differents species.This paper sets four levels of habitat destruction: habitat is not damaged and 5%, 15%, 30% destruction of habitat. The former sets the exotic species has a strong competitive and has the same competitive with the native species, simulate native species and exotic species have different seed germination, seed dispersal mode and seed yield the three kinds of different life history parameters and both of them distribution and landscape pattern changes; when habitat is destructed, simulate native species and exotic species with different life history parameters then theirs distribution of the landscape pattern and habitat changes. Then using the model to simulate the typical exotic species along the Qinghai-Tibet Railway. Stellera chamaejasme Linn. diffusion process in the local species of Kobresia pygmaea and Kobresia humilis community.By comparing the above analysis of different cases of external factors to affect the spread of invasive species, mainly the following conclusions:(1) In the habitat is destroyed 5%, exotic species invasion basically does not affect, and moderate habitat destruction is more conducive to exotic species invasion, when the habitat break level increased to 30% and above, alien species invasion process is subject to strong obstacles, diffusion slowed down;(2) With habitat destruction, less competitive species are located in crowded areas of habitat destruction, with destruction of habitat as a barrier against the invasion of more competitive species, which is the early stage of the invasion of exotic species in habitat is damage in the area ;(3) For seed yield, if the seed production of exotic species higher than native species, the exotic species can successfully invade; when the seed yield of exotic species and native species is sub-equal or slightly lower than the native species, if the exotic species has the same competitiveness to the local species, the native to exotic species can get symbiotic state, if the competitive ability of exotic species higher than native species ,the invasive species can successfully invade and the gradual extinction of local species; when the seed yield of exotic species is 2/3 of the the seed yield of native species, no matter how competitive exotic species, invasive exotic species will fail;(4) For seed germination, the seed germination of the exotic species is higher than the native species, the exotic species can successfully invade and make the gradual extinction of native species; when the germination rate of exotic species and germination rate of the local variety have the same value, if the exotic species competitiveness is the same to the native species , native and exotic species can get symbiotic state, if the competitive ability of exotic species higher than native species ,the invasive species can successfully invade and the gradual extinction of local species; when the germination rate of exotic species is 3/4 of the native species , if the exotic species and the native species competitiveness have the same value , exotic species will gradual demise and failure, if the competitive ability of exotic species is higher than the native species, the invasive species successfully invade and the native species will gradual extinction ;when the germination rate of exotic species is 1/2 of the native species seed germination rate , regardless of how competitive exotic species, invasive exotic species will fail;(5) For seed dispersal, the exotic species has medium-distance spread and the the native species has long-distance spread, exotic species has short-distance spread and native has long-distance spread, exotic species has short-distance spread and native has media-distance spread, invasive exotic species will fail.(6) Stellera chamaejasme Linn. extent of the destruction of the habitat is less than 30% compared to intact habitats will speed up, intact habitats and habitat destruction more than 30% of its spread has slowed down. Therefore, the destruction of the Qinghai-Tibet Railway is led to the invasion of exotic species is one of the important reasons to maintain well native vegetation, reduce the number of exotic species of seeds and seed germination rate of control of invasive species is an effective way.