DISSERTATION RESEARCH: Belowground Bud Bank Populations as Regulators of Vegetation Responses to Ecosystem Drivers in African Grasslands

在草原和稀树草原生态系统中，地下营养芽（芽库）的数量对当地植物种群的持续和动态起着关键作用。在许多草原上，这种芽库，而不是种子，是植物繁殖、茎的季节性更新和当地人口可持续性的主要来源。事实上，在高草草原上，高达99.6%的植物茎是由芽而不是种子形成的。芽库可能在草原对全球环境变化的响应中发挥关键作用。土壤种子库的总体生态学已经得到了很好的研究，但与之不同的是，芽库的重要性仍然没有得到充分的重视和理解。本研究解决了芽库对植被和生态系统动态影响的四个问题，并验证了在北美草原上，火灾、放牧和气候变率等关键因素对植物群落多样性和生产力的影响可能主要通过它们对地下芽库动态的影响来调节的假设。本论文的加强项目检验了这些生态假设的一般性以及北美草原上火灾和放牧的作用，并将研究扩展到测试芽库在博茨瓦纳奥卡万戈三角洲地区草为主的生态系统中的关键作用，博茨瓦纳是非洲南部一个具有重要生态和社会经济意义的地区。了解芽库动态将有助于预测草原和稀树草原对长期环境变化的反应，以及对其三个主要生态驱动因素（火灾、放牧和水文制度）变化的反应。

In grassland and savanna ecosystems, the population of belowground vegetative buds (the bud bank) plays a key role in local plant population persistence and dynamics. In many grasslands, this bud bank, rather than seeds, is the primary source for plant reproduction, the seasonal regeneration of stems, and local population sustainability. In fact, in tallgrass prairie as many as 99.6% of plant stems are derived from buds, not seeds. Bud banks may play a key role in the response of grasslands to global environmental change. Unlike soil seed banks, whose general ecology has been well studied, the importance of bud banks remains under-appreciated and poorly understood. This research addresses four questions about the effects of bud banks on vegetation and ecosystem dynamics, and test the hypothesis that in North American grasslands, the effects of key factors such as fire, grazing, and climatic variability on plant community diversity and productivity may be mediated principally through their effects on belowground bud bank dynamics. This dissertation enhancement project tests the generality of these ecological hypotheses and the roles of fire and grazing across North American grasslands, and extends the research to test the key role of bud banks in the grass-dominated ecosystem of the Okavango Delta region of Botswana, an area of great ecological and socio-economic importance in southern Africa. Understanding bud bank dynamics will help predict responses of grasslands and savannas to long-term environmental change and to alterations in their three main ecological drivers: fire, grazing, and hydrologic regimes.