Aboveground productivity and community stability tend to keep stable under long-term fencing and nitrogen fertilization on restoration of degraded grassland

•Using community productivity and stability to estimate restoration of degraded steppe.•Community productivity did not continuously increase as restoration duration extended.•Degraded steppe reached optimal status after seven years’ restoration.•Community stability decreased in early phase, but maintained stable in later phase.•Species asynchrony and dominant species stability regulated community stability.