Abstract:

During the long-term recovery and restoration of shrub vegetation in desert-grassland regions， the issue of declining shrub morphology and function has become increasingly prominent， posing significant challenges to the sustainable ecological recovery of these areas. Understanding the effects and evolutionary trajectories of shrub vegetation restoration at the regional scale， and exploring how these trajectories depend on contextual factors （such as time since restoration began） and environmental factors （such as precipitation， mean annual temperature， and soil type）， is an important scientific need. In this study， this challenge was addressed by studying desert grassland ecosystems in northern China using a Meta-analysis of 86 Chinese and English scientific sources published from 2000-2023. This Meta-analysis integrated 135 shrub morphological and functional data from 64 independent experiments to carry out a systematic study. The results showed that： 1） During restoration root biomass， crown width and reproductive branch number of shrubs were enhanced by 50%-150% （P<0.05）， but the recovery effect for above-ground biomass was weaker-typically 3%-15% （P>0.05）. 2） With increasing number of years since restoration commencement， shrub biomass decreased by 50%-70% （P<0.05）； as precipitation increased， the restoration effect on branch number， crown width and number of reproductive branches increased by 30%-50% （P>0.05）； warmer temperatures during restoration resulted in a 20%-50% decrease in the shrub vegetation plant height， reproductive branch number， total branch number， and basal diameter （P>0.05）. In comparison with undegraded native soil habitats， sandy degraded habitats significantly promoted the recovery of shrub plant height， basal diameter and number of branches （P<0.05）， but limited the recovery of above-ground biomass and crown width （P>0.05）. 3） The environment-dependent characterization of the shrub restoration effects described above was marked by multiple threshold effects： precipitation （240 mm， P>0.05）， restoration duration （36 years， P<0.05）， and mean annual temperature （7.7 ℃， P<0.05）. The overall restoration benefit of shrubs changed from positive to negative for data lying before and after the threshold. In summary， where duration of shrub vegetation restoration and reconstruction in the desert grassland exceeded 20 years， there was a definable trajectory of decline and evolution of shrub morphology （branch number， plant height， etc.） and function （biomass）. Within this process of transformation there were multiple positive and negative environmental threshold effects within the restoration process. In the future， it will be necessary to formulate restoration and management strategies that are appropriate to the environment and take account of these environmental threshold intervals in conjunction with the more favorable shrub restoration capacity of sandy habitats in order to optimize the sustainability of restoration of shrub vegetation.

Key words: desert steppe, vegetation restoration, shrub decline, Meta-analysis