Dynamic characteristics of vegetation communities in natural recovery oil well development sites

This study was undertaken to reveal the succession rules of vegetation community in natural recovery oil well sites, and to explore the relationship between vegetation community characteristics and soil physical and chemical properties in oil well sites with different restoration years. Vegetation communities and soil physical and chemical properties were determined in typical oil development areas of Loess Plateau in northern Shaanxi province in China. The number of families, genera, and species of plant communities increased with length of time of restoration. Leguminosae, Compositae, and Gramineae were predominant. Herbage plants coverage, number of species, individual number, and aboveground biomass increased by 54.04%, 160.00%, 168.68%, and 49.21%, respectively, from recovery years 1 ~ 20. Shannon-Wiener and Margalef indices of plant communities increased with increasing restoration time. The Pielou index initially increased and then decreased. After 20 years of restoration, the community coverage and individual number were significantly higher than those of the natural restoration grassland (P < 0.05). However, species number and biomass were still lower than those of the natural restoration grassland (P < 0.05). With increasing length of restoration, soil pH, total petroleum hydrocarbon, available phosphorus, and soil carbon/nitrogen ratio decreased significantly. Soil organic carbon, total nitrogen, and nitrogen/phosphorus ratio increased by 6.73%, 75.00%, and 93.23%, respectively. Soil total phosphorus did not change significantly (P > 0.05). Community species diversity index showed a strong synergistic relationship with soil total petroleum hydrocarbon content, soil bulk density, and total nitrogen. The explanation rate of soil physical and chemical indicators to species changes was 62.13%. However, the response of different species to soil nutrient indicators differed. In general, the relationship between vegetation community and soil nutrients was synergetic during the natural restoration of oil well site. The vegetation community generally recovered in the direction of natural restoration grassland.