Key message Mature Caragana stenophylla shrubs facilitated intraspecific sapling establishment by two mechanisms: microhabitat amelioration and protection against herbivory. Facilitation was mediated by climate, grazing, and sapling age. Context Pre-existing shrubs could facilitate sapling establishment of woody plants; however, how these facilitation vary across abiotic and biotic stress gradients and the underlying mechanisms remain unclear. Aims The aim of this study is understanding the facilitation of shrub on sapling establishment and how the two underlying mechanisms, microhabitat amelioration and protection against herbivory, vary across climatic aridity gradients, grazing gradients, and sapling age. Methods We conducted field sowing experiments to examine the facilitation of mature Caragana stenophylla Pojark on intraspecific sapling establishment. Results Facilitation of C. stenophylla on sapling survival increased as drought stress, grazing intensity, and sapling age increased. Microhabitat amelioration increased as drought stress and sapling age increased. Similarly, protection against herbivory increased as drought stress, grazing intensity, and sapling age increased. Relative importance of microhabitat amelioration increased as drought stress increased, and relative importance of protection against herbivory increased as grazing intensity and sapling age increased. Conclusion Facilitation of shrub on sapling establishment involves both microhabitat amelioration and protection against herbivory. Facilitation, the two mechanisms, and relative importance between the two mechanisms would all be affected by climatic aridity, grazing intensity, and sapling age. Shrub establishment has a positive feedback effect. |
