【解释热带森林结构】Franziska Taubert Markus Wilhelm Jahn Hans-Jürgen Dobner Thorsten Wiegand and Andreas Huth. The structure of tropical forests and sphere packings. PNAS 2015 doi:10.1073-pnas.1513417112
The search for simple principles underlying the complex architecture of ecological communities such as forests still challenges ecological theorists. We use tree diameter distributions—fundamental for deriving other forest attributes—to describe the structure of tropical forests. Here we argue that tree diameter distributions of natural tropical forests can be explained by stochastic packing of tree crowns representing a forest crown packing system: a method usually used in physics or chemistry. We demonstrate that tree diameter distributions emerge accurately from a surprisingly simple set of principles that include site-specific tree allometries random placement of trees competition for space and mortality. The simple static model also successfully predicted the canopy structure revealing that most trees in our two studied forests grow up to 30–50 m in height and that the highest packing density of about 60% is reached between the 25- and 40-m height layer. Our approach is an important step toward identifying a minimal set of processes responsible for generating the spatial structure of tropical forests.
一项研究使用树冠的随机聚集，解释了诸如树木尺寸分布和叶面积分布等森林属性，这些属性衡量了热带森林结构，可以用于估计地面以上的生物质和碳储存。(来源：EurekAlert!)
【气候、地形与沉积物尺寸】Clifford S. Riebe Leonard S. Sklar Claire E. Lukens and David L. Shuster. Climate and topography control the size and flux of sediment produced on steep mountain slopes. PNAS 2015 doi:10.1073-pnas.1503567112
Weathering on mountain slopes converts rock to sediment that erodes into channels and thus provides streams with tools for incision into bedrock. Both the size and flux of sediment from slopes can influence channel incision making sediment production and erosion central to the interplay of climate and tectonics in landscape evolution. Although erosion rates are commonly measured using cosmogenic nuclides there has been no complementary way to quantify how sediment size varies across slopes where the sediment is produced. Here we show how this limitation can be overcome using a combination of apatite helium ages and cosmogenic nuclides measured in multiple sizes of stream sediment. We applied the approach to a catchment underlain by granodiorite bedrock on the eastern flanks of the High Sierra in California. Our results show that higher-elevation slopes which are steeper colder and less vegetated are producing coarser sediment that erodes faster into the channel network. This suggests that both the size and flux of sediment from slopes to channels are governed by altitudinal variations in climate vegetation and topography across the catchment. By quantifying spatial variations in the sizes of sediment produced by weathering this analysis enables new understanding of sediment supply in feedbacks between climate tectonics and mountain landscape evolution.
对美国加州High Sierra 集水区的沉积物的一项研究发现，寒冷、陡峭的高海拔山坡产生的沉积物比低而缓的山坡产生的沉积物更粗糙，这提示了气候、地形和风化率的变化可能通过影响沉积物尺寸从而塑造山地地貌的演化。(来源：EurekAlert!)
【生物量生产率】 M. Campioli S. Vicca S. Luyssaert J. Bilcke E. Ceschia F. S. Chapin III P. Ciais M. Fernández-Martínez Y. Malhi M. Obersteiner D. Olefeldt D. Papale S. L. Piao J