Re-established Vegetation Response To Climate Factors On Surface Mined Land

The potential impact of climate change on the long-term stability of the reconstructed ecosystem in mining area has aroused wide academic concern.Considering the drastic changes of biological and abiotic components such as soil hydrology and microclimate,vegetation response to climate factors in reclaimed mined areas may be different from the surrounding undisturbed areas.This study aims to provide scientific basis for predicting climate change impacts on reclaimed ecosystems,optimizing the reclamation technologies and ensuring the long-term stability of these reconstructed ecosystems,by comparing differences of vegetation response to climate factors between reclaimed mined lands and their adjacent unmined lands,and analyzing the causes for these differences.Based on the time series data of enhanced vegetation index(EVI)(135 images in total)and corresponding meteorological data in the growing season from 1997 to 2017,the response of vegetation dynamic change to climate variability in reclaimed plots and undisturbed plots in Pingshuo mining area was compared using the generalized additive model.(1)Climate factors.The climate factors of reclaimed vegetation are temperature,rainfall,air humidity and wind speed variability,while those of undisturbed vegetation are only temperature and air humidity variability.(2)Climate variability explains the EVI change of 19.95%-46.46%in reclaimed plots and 0.70%-1.74%in undisturbed plots,indicating that reclaimed vegetation is far more sensitive to climate variability than undisturbed vegetation.(3)Climate variables have significantly different time effects on reclaimed vegetation and undisturbed vegetation.The effect of climate variables in reclaimed area is greater than that in undisturbed area.The causes for the difference between reclaimed vegetation and undisturbed vegetation in response to climate variables are as follows.(1)Rainfall variability contributes to EVI of reclaimed sample plot is 0.21%?6.20%,while there is no significant impact on undisturbed sample plot.Although field water holding capacity of the reconstructed soil after 20 years is close to or greater than that of the natural soil,the thickness of the reconstructed soil layer in reclaimed area(?1 m)is far less than that of the loess layer in the natural area(up to 35 m).It indicates that rather than poor soil hydrological characteristics,the thin soil layer is the major reason that reclaimed vegetation is more dependent on rainfall then natural vegetation.(2)Due to the acceleration of wind by the mountain terrain in the reclaimed area(120 m?150 m higher than the surrounding),wind speed variability only affects the reclaimed vegetation.(3)The contribution of temperature variability on vegetation growth in reclaimed sample plots(12.89%?40.26%)is much greater than that in undisturbed sample plots(0.70%?1.17%).The land surface temperature retrieval shows that surface temperature of the reclaimed sample plots is lower than that of the undisturbed sample plots as a whole,indicating that the acceleration of wind by mountain terrain of the South dump and low temperature caused by the block of shady slope are the main reasons for the stronger temperature constraints on the reclaimed vegetation.(4)The contribution of air humidity on reclaimed vegetation(0?12.75%)is greater than that of undisturbed vegetation(0%?0.57%),which is mainly due to higher vegetation fragmentation and greater edge effect in the reclaimed area.(5)The time-accumulation effect of climate variables on reclaimed vegetation is longer than that of undisturbed vegetation,especially the average temperature factor(45?65 days in reclaimed plots and 10?15 days in undisturbed plots).It shows that compared with undisturbed vegetation,reclaimed vegetation recovers more slowly from adverse climate events.The damaged resilience of reclaimed ecosystem further aggravates the restrictions of climate variability on the reclaimed vegetation growth.Literature analysis and investigation of typical mining areas in multiple bioclimatic zones show that factors caused the change of the vegetation response to climate generally exist in most open-pit mines.The divergence of succession stage and succession direction makes the reconstructed vegetation in the mining area very different from the surrounding undisturbed area in species composition,community structure and coverage.Taking Yimin Open-pit Mine for example,the vegetation type on undisturbed area is herb community with high coverage,and a total of 62 species of herbs are found;in contrast,herbaceous plant coverage of the reclaimed area is sparse,with only 47 herbaceous species,and the community is combined of lichen crust,moss crust and vascular plants.The soil layer in the reclaimed area is thinner than that in surrounding undisturbed area.The thickness of reclaimed soil in desert and grassland is less than 0.35 m,and that in the Loess Plateau is less than 1 m,which is far less than the depth of soil water available to plants under natural conditions(herbaceous plants can be as deep as 1 m,woody plants can be 2 m or deeper).The restriction of thin soil layer and the limitation of available water would make the reclaimed vegetation more sensitive to rainfall variability and more vulnerable to high temperature stress.The changes of ecosystem components such as vegetation community composition,soil and geological layer group would lead to the different response of reclaimed vegetation to climate from the undisturbed area.There are three negative effects on the reconstructed ecosystem caused by the changes of hydrology,microclimate and the response of reconstructed vegetation to climate.First,compared to the thick loess layer in undisturbed area,the reconstructed soil layer is less than 1m and the water holding capacity is poor in reconstructed mining area,which makes the reclaimed vegetation more dependent on rainfall and more vulnerable under drought stress.Second,the temperature reduction caused by the change of terrain in the reclamation area shortens the growth period of reclaimed vegetation by about 17%.Third,hostile microclimate and inappropriate species selection lead to the secondary degradation of locally reconstructed vegetation(e.g.S5 sample plot).It can be inferred from the general process of open-pit mining that the change of the response of the reconstructed ecosystem to the climate caused by the environmental post-effect of open-pit mining will restrict its ecosystem productivity,affect the species composition,community structure and succession direction,and threaten the long-term climate stability of the reconstructed ecosystem in the mining area.There are implications for reclamation research and practice from the conclusions.Current reclamation techniques and reclamation strategies may be difficult to maintain the long-term climate stability of the reconstructed ecosystem in the mining area under the impact of climate change.Optimization of site hydrological,microclimate conditions,and plant species selection should be considered in reclamation design.So as to reduce the negative impact of post mining environmental effects and improve the climate stability of the reconstructed ecosystem.Future research should pay more attention to the response of reclaimed vegetation to different dimension of climate to establish a foundation for accurately predicting the impact of climate change on the reconstructed ecosystem in the mining area.Mechanism of the change on response of vegetation to climate caused by environmental post-effect in open-pit mining and its impact on the reconstruction of ecosystem in the mining area should be further studied,in order to help us deal with the dual challenges of environmental problems caused by mining and climate change.