Impact of center pivot irrigation on vegetation dynamics in a farming-pastoral ecotone of Northern China: A case study in Ulanqab, Inner Mongolia

•The number of center pivot irrigation (CPI) in Ulanqab first increased and then decreased during 2002–2017.•Both the average NDVI and the percentage of significant improvement inside the CPI are large than those outside the CPI.•Center pivot irrigation caused vegetation degradation within 10,000 m surrounding the CPIs.•There is a significant positive correlation between the size of CPIs and the degree of vegetation degradation.