Collaborative Research: Effects of Soil-Borne Resources on the Structure and Dynamics of Lowland Tropical Forests

尽管目前人们对热带森林作为全球碳循环的关键组成部分和生物多样性的中心很感兴趣，但我们对森林属性（例如，动态、多样性、结构）和这些森林生长环境的物理特性之间的相互关系仍然知之甚少。近年来，已有数据集描述了全球约10%的热带树种多样性的生长、死亡和补充情况。这些数据来自热带森林科学中心（CTFS）协调的大型森林动态样地网络的发展，并使用与巴拿马巴罗科罗拉多岛（BCI） 50公顷森林动态样地调查和普查相同的方法建立。正如来自BCI样地的数据在我们理解在当地尺度上发挥的生态过程的群落水平后果方面发挥了突出作用一样，我们将展示这些样地现在如何为研究热带生态学中一个古老的问题提供了前所未有的机会：土壤资源如何影响样地之间观察到的森林结构和人口流失率的变化，以及样地内栖息地类型的变化？为了实现这一目标，我们提出了三套衡量标准。在9个样地，我们将使用水文模型（TOPMODEL）描述全年和整个样地的土壤水分可用性变化。该模型基于降雨、水流数据和当地地形来预测土壤水分饱和亏缺。其次，在五个目前缺乏土壤数据的地块上，我们将在标准化的、地形定义的栖息地类型中取样土壤化学性质。第三，在相同的样地，我们将使用菌根和非菌根先驱物种进行幼苗生长试验，以评估每种生境类型的土壤养分植物有效性。这些测量将使我们能够在两个空间尺度上解决问题。在图间尺度上，我们将能够询问茎密度和基底面积，以及整个社区的生长、死亡和补充模式，如何与水分有效性和土壤肥力相关联。在样地范围内，我们将询问物种是否对特定的水文生态位表现出专门化，以及栖息地类型在土壤肥力、周转率和当地物种丰富度方面是否存在差异。解决这些关于土壤资源和植被特征之间的相关性的广泛问题，将使我们能够完善未来的假设，旨在了解种群和分布的种间变化的机制基础。这项研究将首次对热带森林生长的环境背景进行标准化的大规模测量。我们的跨大陆测试生态系统功能和群落组织问题的方法很少被尝试过，但如果我们要提高我们对生态概括的生物地理和生物物理限制的理解，这将是必不可少的。了解水分和养分有效性的变化如何决定森林结构、组成和动态，并通过生态位划分潜在地影响当地多样性，对于预测未来植被对气候变化的响应至关重要，也将为指导管理以保护森林多样性提供第一步。国内合作者的积极参与和CTFS的数据共享确保了该项目的广泛传播和应用。

Despite current interest in tropical forests as key components of the global carboncycle and as centers of biodiversity,we remain largely ignorant of the inter-relationshipsamong forest attributes (e.g.,dynamics,diversity,structure),and the physical propertiesof the environments in which these forests grow.In recent years datasets have becomeavailable describing growth,mortality and recruitment of approximately 10%of theglobal diversity of tropical tree species.These data result from the development of anetwork of large-scale forest dynamics plots coordinated by the Center for TropicalForest Science (CTFS),and established using methods identical to those used to surveyand census the 50-ha Forest Dynamics Plot on Barro Colorado Island (BCI),Panama.Just as data from the BCI plot have played a prominent role in our understanding of thecommunity-level consequences of ecological processes played out at local scales,we willshow how these plots now provide an unprecedented opportunity to examine a venerablequestion in tropical ecology:How do soil-borne resources influence the variation in foreststructure and demographic turnover rates observed among plots,and among habitat typeswithin plots?To achieve this objective we propose three sets of measurements.At nine plotsites we will characterize variation in soil-moisture availability through the year andthroughout the plots using a hydrological model (TOPMODEL).This model predictssoil-moisture saturation deficit based on rainfall,stream-flow data and local topography.Second,at five plots currently lacking soils data we will sample soil-chemical propertieswithin standardized,topographically-defined habitat types.Third,at the same plots wewill perform seedling growth experiments using mycorrhizal and non-mycorrhizalpioneer species to assess plant-availability of soil nutrients for each habitat type.Thesemeasurements will allow us to address questions at two spatial scales.At the among-plotscale we will be able to ask how stem density and basal area,as well as community-widepatterns of growth,mortality and recruitment,correlate with moisture availability and soilfertility.At the within-plot scale we will ask whether species exhibit specialization toparticular hydrological niches,and whether habitat types differ in soil fertility,inturnover rates,and in local species richness.Resolution of these broad questionsconcerning correlations among soil-borne resources and characteristics of the vegetationwill in turn permit us to refine future hypotheses aimed at understanding the mechanisticbasis for interspecific variation in demographics and distribution.This study will provide the first standardized large-scale measurements of theenvironmental context within which tropical forests grow.Our trans-continental approachto testing questions of ecosystem function and community organization has rarely beenattempted,but it will be essential if we are to improve our understanding of thebiogeographic and biophysical limits to our ecological generalizations.Understandinghow variation in water and nutrient availability determines forest structure,compositionand dynamics,and potentially influences local diversity through niche partitioning,willbe essential to predicting future vegetation responses to climate change and will alsoprovide a first step in guiding management to protect forest diversity.Wide disseminationand application of the results of this project is ensured by the active participation of in-country collaborators,and by data sharing through CTFS.