COLLABORATIVE RESEARCH: Mechanisms of tree recruitment limitation across a savanna soil moisture availability gradient

热带草原或稀树草原覆盖了地球上20%以上的土地，养活了世界上大多数牲畜和野生食草动物，因此养活了世界上很大一部分人口。在它们的边缘，稀树草原经常变成森林，它们可以缩小或扩大，这取决于森林是前进还是后退。似乎有三个主要因素可以解释稀树草原和森林之间的界限：杀死树木的火灾，维持树木生长的降雨，以及食草动物对树苗和草的放牧。这个项目将在世界上最多产的热带草原之一——坦桑尼亚的塞伦盖蒂草原上进行一项非常大的实地试验，以测试哪种火、水和放牧的组合能最好地维持热带草原。来自美国和坦桑尼亚的研究人员将把优势树种的种子和幼苗种植在降雨量高低不等的不同地点的围栏或非围栏、燃烧或未燃烧的地区，然后在三年内测量这些树木的成功情况。除了让我们对稀树草原为什么会在哪里出现以及它们的边界在未来可能如何变化有了新的理解之外（这些知识对我们管理牲畜和提供食物的能力很重要），这项研究还将培训新的科学家，促进国际合作，并在发展中国家建立科学能力。该项目将帮助培训两名坦桑尼亚科学家以及密苏里大学的一名坦桑尼亚研究生和北卡罗来纳州维克森林大学的一名博士后学者。为了在非洲建立科学能力，该项目将为坦桑尼亚Sokoine农业大学的学生提供关于数据收集和统计的年度讲习班。

Tropical grasslands, or savannas, cover over 20 percent of the land on Earth, support most of the world's livestock and wild herbivores, and thus feed a large fraction of the world's population. At their edges, savannas often grade into forest, and they can shrink or expand depending on whether the forests advance or retreat. Three major factors seem likely to account for the boundary between savanna and forest: fire that kills trees, rainfall that sustains them, and the grazing of the herbivores on tree seedlings and grass. This project will mount a very large field experiment in one of the most productive savannas in the world, the Serengeti of Tanzania, to test which combinations of fire, water, and grazing best maintain savanna. Researchers from the U.S. and Tanzania will plant seeds and seedlings of dominant trees into fenced or unfenced, and burned or unburned areas within different sites that range from low to high rainfall, and then measure the success of the trees over three years.Besides giving us new understanding of why savannas occur where they do and how their boundaries may change in the future, knowledge important to our ability to manage livestock and provide food, this research will train new scientists, promote international collaboration, and build the capacity for science in the developing world. The project will help train two Tanzanian researchers plus a Tanzanian graduate student at the University of Missouri and a postdoctoral scholar at Wake Forest University in North Carolina. To build scientific capacity in Africa, the project will offer annual workshops on data collection and statistics for students at Tanzania's Sokoine University of Agriculture.