Impact of extreme climates on vegetation from multiple scales and perspectives in the Agro-pastural Transitional Zone of Northern China in the past three decades

Climate conditions greatly control vegetation dynamics in terrestrial ecosystems, and global warming has become an indisputable fact, triggering a wide range of research on vegetation responses. However, evidence of vegetation responses to extreme climates is still inadequate, especially in arid and semiarid areas. Here, we explicitly investigated the impact of extreme climate on different vegetation types from 1986 to 2015 in the Agro-pastural Transitional Zone of Northern China (APTZNC), by using six extreme temperature and precipitation indices and the Normalized Difference Vegetation Index (NDVI) at monthly, seasonal, and yearly scales. The results showed that (i) the whole area showed a significant warming and nonsignificantly drying trend in terms of extreme climates; correspondingly, the NDVI increased in most areas with the proportion of 81.94% and decreased in some areas with a proportion of 18.06%; (ii) the time lag effects of extreme precipitation and extreme temperature on vegetation were at least two months and at least three months, respectively; and (iii) extreme temperature and precipitation had significant constraint effects on vegetation, showing hump shapes with threshold and exponential curves, respectively; (iv) the maximum total precipitation amount in consecutive five-day period (Rx5day) and the maximum value of daily maximum temperature (TXx) had the most considerable relative contributions to the NDVI with proportions of 29% and 23%, respectively. We hope our research will deepen our comprehensive understanding of the relationship between extreme climates and terrestrial ecosystems, with multiple scales, multiple methods, and multiple perspectives, and promote sustainable practices in the arid and semiarid region.