Beyond shrub dieback: Understory plant diversity, soil water and soil carbon storage were improved in a semi-arid region

Shrub plantation is an effective approach for controlling soil erosion and land degradation. However, the extensive dieback on shrubs as a result of climatic changes or soil drought may impair shrub plantations' ecosystem functions in arid and semi-arid regions. In this study, we sampled brown C. korshinskill plantations (shrub dieback > 90%), green plantations (shrub dieback was rarely < 10%) and an over-100 years' natural grassland as the reference. The changes in plant biomass and diversity of understory vegetation, soil water storage (SWS) and carbon storage (SOCs) across of 0-10 m soil profile were analyzed. The results showed that, (i) the understory herbaceous biomass in brown plantations was 134.1 g m  2 and significantly higher by 49.5% than green plantations. The biomass and diversity of perennial forbs and annual/biennial grasses in brown plantations was also increased significantly; (ii) shrub dieback replenished soil water within 1-5 m depth. The SWS under brown plantations was significantly increased by 44.6% compared with green plantations, and reached 84.7% of that in natural grassland; (iii) the SOCs was notably higher in shrub plantations in the 0-10 m soil profile, increasing by 6.68% and 10.3% compared with natural grassland, respectively. SOC accumulation was mostly occurred at depths below 5 m under brown plantations. Overall, beyond shrub dieback, ecosystem functions of plantations were enhanced unexpectedly. The findings suggest that it was a blessing in shrub dieback disguise, understory herbaceous vegetation may maintain ecosystem functions of plantations in the semi-arid region alternatively.