Increased drought frequency causes the extra-compensation of climate wetness on tree growth to fade across inner Asia

Abstract

The marked increase in drought extreme frequency in drylands raises concerns about the stability and sustainability of forest productivity. However, the responses of forests to climate extremes in drylands such as Inner Asia have received limited attention thus far despite their importance for forest sustainability and ecosystem services. After examining the changes on tree growth observed during and after droughts as well as the relations of growth increments associated with climate wetness at 32 forest sites across Inner Asia, we found that the growth compensation by climate wetness can reach 278% in Inner Asia (tree growth increasing 0.39 mm during climate wetness vs decreasing 0.14 mm during droughts), 2.5 times higher than the global average of 93%, reflecting the adaptation of forests in water-deficient areas to high-frequency climate extremes. However, we further observed fading extra-compensation of climate wetness on tree growth since the 1980s, namely decreasing growth enhancements occurring during wet periods, while significantly increasing growth declines occurring during dry periods. Fading extra-compensation on tree growth was leading to persistent and pervasive declines on tree growth rate in the study area. Our results indicate that this fading extra-compensation of climate wetness will weaken the resistance of forests to droughts and potentially reduce the carbon sink strength of forests in Inner Asia.