School for Environmental Research, Charles Darwin University, Darwin, NT 0909, Australia.
Present address: Department of Biological Sciences, Macquarie University, NSW 2109, Australia.
New Phytol. 2011 Jul;191(1):197-209. doi: 10.1111/j.1469-8137.2011.03689.x. Epub 2011 Apr 4.
• We aimed to identify the limits of savanna across Africa, Australia and South America. We based our investigation on the rich history of hypotheses previously examined: that the limits of savanna are variously determined by rainfall, rainfall seasonality, soil fertility and disturbance. • We categorized vegetation on all continents as 'savanna' (open habitats with a C(4) grass layer) or 'not-savanna' (closed habitats with no C(4) grass layer) and used a combination of statistical approaches to examine how the presence of savanna varied as a function of five environmental correlates. • The presence of savanna is constrained by effective rainfall and rainfall seasonality. Soil fertility is regionally important, although the direction of its effect changes relative to rainfall. We identified three continental divergences in the limits of savanna that could not be explained by environment. • Climate and soils do not have a deterministic effect on the distribution of savanna. Over the range of savanna, some proportion of the land is always 'not-savanna'. We reconciled previous contradictory views of savanna limits by developing a new conceptual framework for understanding these limits by categorizing environmental factors into whether they had a positive or negative effect on woody growth and the frequency of disturbance.
• 我们旨在确定非洲、澳大利亚和南美洲各地热带草原的范围。我们的调查基于之前检验过的丰富假说：热带草原的范围由降雨量、降雨季节性、土壤肥力和干扰等因素决定。 • 我们将所有大陆的植被分为“热带草原”（具有 C(4)草层的开阔栖息地）或“非热带草原”（没有 C(4)草层的封闭栖息地），并结合统计方法来研究热带草原的存在如何随五个环境相关因素的变化而变化。 • 热带草原的存在受到有效降雨量和降雨季节性的限制。土壤肥力在区域上很重要，尽管其影响方向相对于降雨量而变化。我们确定了热带草原范围的三个大陆差异，这些差异不能用环境来解释。 • 气候和土壤对热带草原的分布没有决定性影响。在热带草原的范围内，总有一定比例的土地是非热带草原。我们通过将环境因素分为对木质生长和干扰频率有积极或消极影响的因素，为理解这些限制提供了一个新的概念框架，从而调和了先前关于热带草原限制的矛盾观点。
