What Causes Large Local-Scale Variation in Tree Diversity in a Neotropical Forest? An Experimental Approach

小行星9615226 与地形和旱季土壤水分相关的树木多样性在热带森林的小空间尺度上发现了出乎意料的巨大差异。 本研究是一个简单的假设，即热带树木的多样性在很大程度上是由干旱胁迫控制的幼苗和小树苗阶段的实验测试。 在较干燥的地方，一小部分树种可能有足够深的根系作为幼苗，比在较潮湿的地方长时间的干旱生存。 这一假设将通过对移植到单一热带森林内旱季土壤湿度和干旱胁迫程度不同的地点的幼苗进行浇水实验来检验。 该实验将证明，与不浇水的对照地块中的幼苗相比，旱季浇水是否会增加幼苗的存活和生长。 该实验还将显示这种影响是否足够大，以解释在不同地点之间观察到的物种丰富度的巨大差异。 热带森林树种丰富度的全球模式显示出一种强烈的、无法解释的模式，即随着年平均降雨量的增加而增加。 这一研究将有助于我们了解热带森林多样性大的地理变异的潜在原因，以及它是否受苗期事件的控制。 这项研究将改进关于全球气候变化对热带森林多样性丧失的影响的预测。 全球气候模式预测，在下一个世纪，全球年降雨量和季节降雨量的分布将发生重大变化，预计大部分热带地区将变得更加干燥。

9615226 Hubbell Unexpectedly large differences in tree diversity that correlate with topography and dry season soil moisture have been found on small spatial scales in tropical forests. This research is an experimental test of the simple hypothesis that tropical tree diversity is controlled largely by drought stress in the seedling and small sapling stages. In drier sites, a smaller fraction of tree species may have sufficiently deep root systems as seedlings to survive prolonged periods of drought than is the case in wetter sites. The hypothesis will be tested by a watering experiment on seedlings transplanted to sites with greater or lesser dry season soil moisture and drought stress within a single tropical forest. The experiment will demonstrate whether dry season watering increases seedling survival and growth compared with seedlings in non-watered control plots. The experiment will also show whether the effect is sufficiently large to explain the large observed differences in species richness between sites. World-wide patterns of tree species richness in tropical forests show a strong, unexplained pattern of increasing richness with mean annual rainfall. This research will help us to understand the potential causes of large geographical variation in tropical forest diversity and whether it is controlled by events in the seedling stages. The study will improve predictions on the impact of global climate change on loss of tropical forest diversity. Major changes are forecast in the next century by Global Climate Models in the worldwide distribution of annual and seasonal rainfall, and much of the tropics is expected to become drier.