Vegetation Succession Of Large Open-pit Coal Mine In Semi-arid Loess Area

Vegetation restoration is effective for ecological reclamation of mining areas.The growth and restoration of vegetation can characterize the extent and quality of land reclamation in the mining area.Understanding the dynamics of community structure and composition is critical for revealing mechanisms of species coexistence and biodiversity maintenance in the process of vegetation restoration.Pingshuo Open-pit Coal Mine,the land reclamation base of the Ministry of Natural Resources-field scientific research base of Shuozhou,Shanxi,provides us an opportunity to analyze the vegetation succession in different reclamation patterns in an open-pit coal mine waste dump in Loess area.The main results are as follows:?1?Using the method of permanently fixed monitoring sample plot,based on two datasets obtained in 2010 and 2015,the community dynamics of artificial vegetation under four reclamation patterns were analyzed from the 17^th to 22^nd year since reclamation.During this five-year period,the composition of tree species was found relatively stable.The increase in the number of independent individuals with diameter at breast height?DBH??1 cm was in the following order:S??Robinia pseudoacacia×Ulmus pumila×Ailanthus altissima?>S??R.pseudoacacia×Pinus tabuliformis?>S??R.pseudoacacia×P.tabuliformis?>S??R.pseudoacacia?.The annual mortality was in the following order:S?>S?>S?>S?,and recruitment rate was in the following order:S?>S?>S?>S?.The highest mortality and recruitment were each found among the R.pseudoacacia and U.pumila.The net increase in basal area was S?>S?>S?>S?.Interestingly the largest decrease and increment of the basal area were both found in R.pseudoacacia.The average DBH increased in R.pseudoacacia,P.tabuliformis and A.altissima,but decreased in U.pumila.The size class structure of different plots has changed greatly.The small individuals had higher mortality.The population of R.pseudoacacia and A.altissima generally decreased.P.tabulaeformis population basically maintained its original size,and U.pumila population grew rapidly.?2?The species diversity of herbaceous layer under four patterns of artificial vegetation was measured using multiple indicators.The variance ratio?VR?method,the?² test,and the Spearman's rank correlation coefficient test were used to analyze the overall association of the herbaceous plant communities and the association between dominant species pairs.The perennial and mesophyte plants dominated the two surveys of herbaceous plants.Important value of annual or annual/biennial,and mesophytic herb decreased,while the dominance of perennial,xerophytes and intermediate mesophyte herb increased along with succession.The species richness index of herbaceous layers decreased,and the Shannon-Weiner index and Pielou evenness index increased.The positive-negative correlation ratio of the dominant species increased,indicating that the structure of herb community tended to be stable.The species diversity of the herbaceous layer of R.pseudoacacia×P.tabuliformis was moderate,and the community stability was the highest.The overall associations of herbaceous layer of the R.pseudoacacia pure forest was significantly negative,which indicated that the interspecific competition was fierce.?3?The linear mixed model was used to explore the effects of tree size,neighborhood competition and environmental factors?soil nutrients and topographic factors?on the growth of artificial vegetation.Multivariate stepwise regression method was used to analyze the influencing factors of species diversity in herbaceous layer.Tree size was typically the most important predictor of growth in 17²2 years of reclamation.Tree indices?average height,average DBH and canopy openness?and soil factors?pH,organic matter and available phosphorus content?together affected the species diversity of the herbaceous layer after 22 years of reclamation.?4?Based on the BEF?Biodivesity-ecosystem functioning?experimental plot,the survival rates and individual growth of artificial vegetation and natural invasion characteristics of herbaceous layer under 15 reclamation patterns were compared,and the influencing factors of the survival rate of artificial vegetation and the species diversity of herbaceous layer were analyzed by multiple stepwise regression.After five years of reclamation,the survival rates of P.tabulaeformis pure forest,R.pseudoacacia and P.tabulaeformis mixed forest,and P.tabulaeformis and Hippophae rhamnoides mixed forest were significantly higher than other reclamation patterns.There were significant differences in the survival rates of the four experimental species,which were characterized by P.tabulaeformis>R.pseudoacacia>Caragana korshinskii>H.rhamnoides.Reclamation pattern and soil nutrient content had no significant effect on the survival of most tree species.Soil pH and available phosphorus content had the most significant effect on species diversity of herbaceous layer in early succession.?5?The method of combining permanently fixed monitoring plots with traditional sampling plots was used to compare the differences in species diversity of herbaceous layer and soil nutrient content under artificial restoration and natural restoration approaches.After five years of restoration,there was no significant difference in species diversity of herbaceous layer and soil nutrient content between the artificial community under 15 reclamation patterns and the spontaneously restored community,which were lower than the original landform level.In the short term,the effect of vegetation restoration on soil nutrient improvement was relatively limited.After 22years of restoration,the soil nutrient content of artificial plant communities under four reclamation patterns and spontaneously restored plant communities has exceeded the original landform.The species diversity of herbaceous layer of the former has approached or exceeded 90%of the original landform,while the latter only restored to68.50%of the original landform,and it was difficult to form a composite structure of arbor,shrub and herb in a short time.