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，但我们仍然在很大程度上忽视了森林属性之间的相互关系（例如，动态，多样性，结构），以及这些森林生长的环境的物理特性。近年来，数据集已经可以描述大约10%的全球热带树种多样性的生长，死亡和补充。这些数据来自热带森林科学中心（CTFS）协调的大规模森林动态图网络的开发，并使用与巴拿马巴罗科罗拉多岛（BCI）上50公顷森林动态样地调查和普查相同的方法建立。正如BCI样地的数据在我们理解当地尺度上生态过程的生态水平后果方面发挥了突出作用一样，我们将展示这些地块现在如何提供一个前所未有的机会来研究热带生态学中一个值得尊敬的问题：土壤资源如何影响森林结构和人口周转率的变化，以及在地块内的栖息地类型？为了实现这一目标，我们提出了三套测量方法。在九个样地，我们将使用水文模型描述土壤水分有效性在全年和整个样地中的变化（TOPMODEL）。该模型根据降雨量、径流数据和当地地形预测土壤水分饱和度不足。其次，在目前缺乏土壤数据的五个地块，我们将在标准化范围内对土壤化学性质进行采样，地形定义的栖息地类型。第三，在相同的地块上，我们将使用菌根和非菌根先锋物种进行幼苗生长实验，以评估每种生境类型土壤养分的植物有效性。这一实验将使我们能够在两个空间尺度上解决问题。在样地尺度上，我们将能够询问树干密度和断面积，以及整个群落的生长、死亡和补充模式与水分供应和土壤肥力之间的关系。在样地内尺度上，我们将询问物种是否表现出对特定水文生态位的专门化，以及栖息地类型是否在土壤肥力方面存在差异，周转率，和当地物种丰富度。解决这些广泛的问题，有关土传资源和植被特征之间的相关性，反过来将使我们能够完善未来的假设，旨在了解种间差异的人口统计学和分布的机制基础。这项研究将提供第一个标准化的大规模测量的环境背景下，热带森林生长。我们的跨-用大陆的方法来检验生态系统功能和群落组织的问题很少有人尝试，但如果我们要提高对生态学概括的地理和生物物理限制的理解，这将是必不可少的。了解水和养分的有效性如何变化决定了森林的结构、组成和动态，并通过生态位划分潜在地影响当地的多样性，将是至关重要的预测未来植被对气候变化的反应，也将提供指导管理，以保护森林多样性的第一步。广泛传播和应用这个项目的结果是由国内合作者的积极参与，并通过CTFS共享数据。

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.