Study On Guided Restoration Of Damaged Vegetation In Semi-arid Coal Mine Area

The eco-environment of semi-arid mining areas in Western-China is fragile,and the climate conditions are bad.Large-scale coal mining makes the original fragile eco-environment worse and the social ecological environment problems worsen.It is very urgent to realize the sustainable management of mine land and restore its production capacity.It is necessary for the sustainable development of the ecological environment in the mining area to find out the influence of the surface environmental factors change on the vegetation under the condition of coal mining and to explore the effective method of the guided restoration of the plants in the semi-arid mining area.However,there are several basic problems in the guided restoration of damaged vegetation in semi-arid mining areas,such as,to what extent can vegetation self recover?When manual guidance intervention is needed,where to intervention?How to intervene?To what extent?Therefore,chlorophyll fluorescence induction technology,airborne hyperspectral monitoring technology and satellite remote sensing monitoring technology were used to extract the disturbed vegetation in semi-arid mining area from multiple angles and scales in this paper.On the basis of the research on the mechanism of plant damage caused by coal mining collapse and the law of time and space disturbance,the above four basic problems are studied to explore the vegetation guided recovery model in semi-arid mining area,so as to provide the methodological basis for the construction of green mine and the reconstruction and utilization of vegetation in mining area.The research results are as follows:(1)The collapse of coal mining results in the destruction of soil site conditions,the deformation of rapid chlorophyll fluorescence induction curve of plant leaves,the reduction of energy share used for electron transfer in plant leaves,resulting in the gradual inhibition of electron transfer and the reduction of photosynthesis efficiency of plant leaves.The stomatal conductance,photosynthetic rate and transpiration rate decreased with the increase of stomatal limitation.The damage degree of plants in the tensile and compression areas is greater than that in the neutral areas,so the priority should be given to the restoration of damaged plants in the compression and tension areas.The reason for the damage of individual plants in the subsidence area is that the coal mining subsidence forms a large number of cracks on the surface of the earth,destroys the soil structure,increases the evaporation surface of soil water,and accelerates the loss of soil water.At the same time,groundwater is evacuated and the buried depth of phreatic water level is reduced,which affects the supply of groundwater to surface water.Soil water content is the most important factor to affect the photosynthetic physiological activities of plants in semi-arid coal mining subsidence area.The threshold values of soil water content of plants under stress and death were 8.91%and 4.87%,respectively.For the mining area with soil water content less than 8.91%,corresponding soil technology should be adopted in advance to improve soil water content,so as to avoid the rapid deterioration of vegetation caused by the decrease of soil water content.(2)Based on the CARS feature selection algorithm,hyperspectral inversion models of the maximum photosynthetic efficiency(Fv/F_M),leaf relative water content(LRWC)and chlorophyll content value(SPAD)of vegetation leaves was established,and the spatial distribution characteristics of the photosynthetic physiological factors in the mining area scale were obtained.The values of Fv/F_M,LRWC and SPAD were in the range of 0.764-0.822,35.81-52.32%and 30.35-48.41 mg/g respectively.The growth of surface plants in the mining area is disturbed by coal mining,the spatial pattern of original plants is broken,and some areas appear plant degradation,which leads to the increase of spatial variation of photosynthetic physiological elements in leaves and the decrease of spatial autocorrelation.Due to the spatial heterogeneity of soil water content in compression area,extension area and neutral area,the changes of Fv/F_M,LRWC and SPAD of plant leaves in three areas after coal mining collapse also have spatial differences.Compared with compression area and extension area,Fv/F_M,LRWC and SPAD of plant leaves in neutral area are higher.Finally,according to the inversion results of Fv/F_M,the spatial recognition of the stressed areas of plants in the disturbed area of coal mining was carried out.(3)Based on the Airborne Hyperspectral Data and the fully constrained least square method,the surface typical plants in Daliuta mining area are identified,and the influence of coal mining on the spatial and temporal distribution and diversity of typical plant species in semi-arid mining area is analyzed.The matching degree of typical plant classification and extraction results with the real results is 77.41%in general.The distribution of surface plants in the mining area is dominated by shrubs and herbs.The percentage of trees,shrubs and herbs is 15.94%,57.97%and 26.09%,respectively.The main plant diversity of mining area and non-mining area is little affected by the disturbance of surface subsidence.Through the significant analysis of the difference between the main plant diversity index of mining area and non mining area.2-7 years after coal mining collapse,the impact of coal mining on trees is greater,while the important value of shrub and grass plants with relatively strong anti collapse interference ability is increased.8-12 years after collapse,the growth site conditions are restored,the vegetation community structure tends to be stable,and the important value of trees and plants is increased.12 years after collapse,the important value of plants in the collapse area is gradually stable.In order to ensure the sustainability of vegetation restoration in semi-arid mining area,the period of restoration management should be at least 12 years.(4)From 2001 to 2016,NDVI of vegetation in Shendong central mining area showed a phenological periodic change.According to the analysis of NDVI difference between mining area and non mining area,the change of NDVI of vegetation in mining area is a process of continuous decrease compared with non mining area in 5years after mining.7 years after mining,vegetation began to recover and NDVI difference began to decrease.By 12 years after mining,NDVI of vegetation in the mining area can basically recover to the level of non mining area.In Shendong central mining area,72.35%and 27.65%of the total central mining area are increased and decreased in vegetation coverage,respectively.The coverage of inter annual vegetation mainly fluctuated in middle and low range.The groundwater depth of 4 m and 8 m are two important thresholds that affect NDVI of vegetation in Shendong mining area.When the groundwater depth is more than 4 m,the wet vegetation with shallow roots will be replaced by the dry vegetation with long roots;when the groundwater depth is more than 8 m,the dry vegetation will be replaced by the sand vegetation.The influence of groundwater depth on vegetation types is mainly realized by affecting soil moisture content.By comparing the composition and abundance differences of typical plant species under different site conditions and different vegetation coverage trends,taking the average abundance value of plant species in the area with increased vegetation coverage as the vegetation reconstruction abundance benchmark,the threshold value of vegetation restoration and reconstruction abundance under different site conditions is between 36.60%and 45.30%.In addition,the different proportion of arbor,shrub and herbage allocation in different site conditions was also obtained.(5)The guided restoration of damaged vegetation in semi-arid mining area should adopt the mode of"both natural restoration and artificial restoration,natural restoration as the main and artificial restoration as the auxiliary".First of all,the treatment of ground fissures in different collapse areas is carried out,and then the key restrictive factors such as groundwater level buried depth,soil moisture content and their threshold recognition are taken as the basic starting point,and whether the restrictive factors recover to the threshold condition is taken as the basic standard to judge the reasonable degree of the vegetation restoration target in the mining area,and the key and targeted guidance to restore the vegetation growth site conditions is carried out.Finally,according to the threshold value of vegetation restoration and reconstruction under different site conditions and the proportion of different arbors,shrubs and herbs,the vegetation community structure was restored by the mode of"first shrub and grass in the early stage of restoration,and then in the later stage of restoration".In this paper,the guided restoration model of damaged vegetation in semi-arid mining area is constructed,and the degree of vegetation self restoration is explained?When manual guidance intervention is needed,where is the intervention?How to intervene?To what extent?So as to provide methodological basis and practical basis for vegetation restoration in semi-arid mines.