Ecological Restoration Dynamics Of Robinia Pseudoacacia Population In An Open Pit Mine In Semi-arid Area

Vegetation restoration is an important method for mining area restoration.Studying the dynamic characteristics of plant population restoration is of great importance to reveal the succession law and the co-existence and maintenance mechanism of species in the process of vegetation restoration in semi-arid area,it is also of great significance to further optimize the allocation model of vegetation ecological restoration.In this study,Robinia pseudoacacia population structure and the ecological niche and spatial distribution dynamics of community associated species were studied by continuous monitoring of fixed quadrats in the ecological restoration area of the south dump of Antai Bao open-pit coal mine in semi-arid area.The main research conclusions are as follows:(1)There was a negative relationship correlation between planting density and survival rate of Robinia pseudoacacia population in the early stage.The survival rate was S1>S3>S4>S2,before recovery 22 years ago,and S3>S1>S4>S2 after 27 years of recovery.In S1 and S3 of Robinia pseudoacacia × Pinus tabulaeformis combination,the overall tree height and DBH of combination of Robinia pseudoacacia were the largest,and the growth of Robinia pseudoacacia first entered the slow stage after 22 years of recovery.The growth of Robinia pseudoacacia in pure S4 and S2 of Robinia pseudoacacia × Ulmus pumila × Ailanthus stinkella was poor and all of them were in the growth stage.With the increasement of recovery years,the proportion of individuals in middle diameter class and middle height class was the largest in all plots.The overall DBH and height structure all shifted to higher diameter class and height class.The proportion of individuals in large diameter class and height class showed S1 and S3>S2>S4.The overall age structure of Robinia pseudoacacia was in an increasing state.The growth potential of Robinia pseudoacacia population age structure in S1,S2 and S3 plots is great,and the future population structure tends to be reasonable.The number of young Robinia pseudoacacia in S4 sample plot decreased gradually,which made it difficult to renew and maintain Robinia pseudoacacia population,and it may be a declining population in the future.In general,Robinia pseudoacacia grew well and the population survival was better in Robinia pseudoacacia × Pinus tabulaeformis mixed forest,while Robinia pseudoacacia broad-leaved pure forest had the worst performance(2)By analyzing the dynamic characteristics of spatial distribution of dominant species in tree layer,we can see that Robinia pseudoacacia grows faster in S1 sample plot and enters the stage of random distribution first.Robinia pseudoacacia shows an aggregation distribution in S2 and S3,and a transition from random distribution to aggregation distribution in S4.In S2 and S3,the distribution of Ulmus pumila was aggregated,and it was aggregation and random alternately in S1 and S4.The distribution of Pinus tabulaeformis was random.The Ailanthus altissima alternates with aggregation and random distribution.Among them,Robinia pseudoacaciaa and Ulmus pumila had higher aggregation intensity.In general,the changes of spatial distribution of different populations are different.Most populations tend to be stable after 17 years of recovery,while a small number of populations show the dynamic characteristics of aggregation distribution and random distribution alternating.(3)According to the important values of major tree species in the tree layer,Robinia pseudoacacia was the dominant species in the community in plots S1,S3 and S4,and the dominance decreased slightly.In S2 plot,the dominance of Robinia pseudoacacia decreased significantly,and was replaced by Ulmus pumila as the dominant species in the community after 22 years of restoration.According to the niche characteristics,Robinia pseudoacacia,Ulmus pumila,Pinus tabulaeformis and Ailanthus altissima had a wide resource utilization capacity,and the resource niche overlaps and similarities were great.With the increase of restoration years,the niche width of Robinia pseudoacacia was the largest and the most stable,and the overlap of resource utilization with other species was also the highest.In general,Robinia pseudoacacia populations showed good performance in the dominance degree and niche width values in various plots,which indicated that Robinia pseudoacacia populations had strong adaptability in the reclaimed land environment.Ulmus pumila invasive species had better performance in the recovery process due to its strong drought tolerance,and also had good development potential.