Research On Mechanism Of Vegetation Degradation And Vegetation Restoration In The Riparian Zone Of Li River

Vegetation degradation in the Lijiang riparian zone has seriously affected its landscape ornamental value.As a world-famous tourist river,vegetation degradation in Lijiang river has attracted much attention in recent years,and vegetation restoration in Lijiang river has become the focus of research.Understanding the mechanism of Lijiang river vegetation degradation is the key to Lijiang river vegetation restoration.Around this central question,this study,starting from the existing vegetation configuration pattern of Lijiang river riparian zone,analyzed the influencing factors of vegetation degradation.On this basis,the Lijiang river forest health status was evaluated,and the vegetation distribution,composition and diversity differences of nearly natural landscape,grazing disturbance landscape,tourism landscape and sand mining landscapes were compared and analyzed,according to different influencing factors.Further,through the corresponding analysis and regression analysis,the research of plant communities' distribution along the potential ecological gradient was conducted to reveal the main environmental impact factors of different landscapes,and the contrasts of environmental factors during the different landscapes and the inundated zones was conducted to reveal the vegetation degradation mechanism.Finally,based on the above results,the Lijiang river vegetation restoration strategy was proposed,and the vegetation restoration experimental study was carried out on the difficult sites of vegetation restoration,to propose a fine vegetation restoration technology.The main results are as follows:(1)The Lijiang river riparian vegetation configuration pattern is divided into Central island natural shrub-herb type(T1),Exurb natural forest arbor-shrub-herb type(T2),Urban artificial arbor-herb type(T3),Gentle-slope-washland natural herb type(T4),Scenic area artificial forest arbor-shrub-herb type(T5)and Suburban natural arbor-shrub-herb type(T6)and the existing vegetation configuration pattern is mainly affected by natural factors and human disturbance factors,among which the natural factor is hydrological disturbance,and the human factor mainly includes tourism disturbance,grazing disturbance and sand mining disturbance.(2)On the whole,there were no obvious regeneration problems in the forest,but there were obvious difficulties in the regeneration of the dominant tree species Pterocarya stenoptera,especially in its dominated forest land.In order to avoid the degradation and disappearance of the native tree species,artificial regeneration should be carried out appropriately.In bamboo-dominated woodlands,the regeneration and diversity of other tree species were inhibited with the increase of bamboo stand basal area.The reasonable density and distribution of bamboo stands should be constructed to achieve the coordination of ecological and landscape effects.The perturbation of grazing,sand mining and tourism human activities is larger in midslope terrace and upland side slope,this makes habitat fragmentation of the Lijiang riparian zone,changed the increased tendency of species richness as far to the river,and makes the distribution of species in the human disturbance landscapes more unstable and species diversity get decreased.(3)In the nearly natural landscape,the dominant environmental factor affecting vegetation is soil fertility;the dominant environmental factors under grazing landscape type are soil structure and texture;Organic matter content and clay content are the dominant environmental factors under tourism landscape;and the main limiting factors for sand mining landscape are available nitrogen and clay particles which can absorb soil nutrient ions.The Lijiang river riparian zone is greatly affected by hydrology,and human disturbance destroys the soil structure and texture of the Lijiang river riparian zone,leading to the erosion of fine particulate matter by water flow,which further reduces soil fertility and available nutrients and leads to vegetation degradation.(4)Based on the gradient distribution of Lijiang river plants in various major environmental impact factors,the vegetation restoration species groups of flood-tolerant,low-phosphorus,soil compact-type,sand grain type and low-organic matter type were selected,which played an important role in the selection of vegetation restoration models.(5)The existing functional vegetation is mainly planted in the Lijiang river intersecting zone,which can be supplemented by landscape species;In the river section with serious vegetation degradation,vegetation restoration is carried out by combining ecological slope protection measures;Urban riparian zones should be planned and improved as a whole to be as close to the natural state as possible while the sand mining activities should be strictly prohibited,awareness of protection should be improved,and the supervision and management should be strengthen.For areas with poor site conditions of gravel beach,the way of "soil dressing-stolon-cover" can be adopted for rapid greening,and the technology of "soil fixation and grassing" and "sand and gravel covering" can be adopted for long-term vegetation restoration.