木本植物多度在草原和稀树干草原中增加的研究进展

Increased abundance of woody plants in grasslands and savannas

木本植物多度在草原和稀树干草原中增加已经成为全球范围普遍发生的现象。为揭示这一现象发生的原因 ,从放牧和气候变化与木本植物多度增加的关系、木本植物多度增加过程中的正反馈作用以及木本植物侵入的关键阶段——幼苗的补充和定居 ,这三个方面综述了目前的研究结果。强调放牧和气候变化之间的相互共同作用 ,可能引发了木本植物向草原和稀树干草原中的入侵 ;而生物引起的正反馈作用则进一步促进了木本植物的扩展。从生态系统干扰的角度 ,讨论了木本植物多度增加机制的复杂性 ,并指出木本植物幼苗补充和定居的连续性和间断性两种方式 ,对于草原和稀树干草原木本植物多度增加的贡献。

Abundance of woody plants has increased substantially in grasslands and savannas worldwide. To explain these phenomena, this paper reviews the three aspects of the related research results, including relationships between grazing or/and climate change and the increased abundance of woody plants, roles of positive feedback in increasing abundance of woody plants, and the recruitment and establishment of seedling of woody plants, which is considered the critical stage for woody plant invasion into the vegetation. It is emphasized that grazing, combined with climate changes, may trigger the encroachment of woody plants into these types of vegetation, and that biological positive feedbacks promote the increase of woody plant abundance within the vegetation. From a view of disturbances in ecosystems, we discuss the complexity of mechanisms for the increased abundance of woody plant, and indicate the contributions of episodic and continuous recruitment and establishment of seedling to woody plant expansion in the vegetation.