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感兴趣，但我们在很大程度上仍然对森林属性(如动态、多样性、结构)和这些森林生长环境的物理性质之间的相互关系一无所知。近年来，已有描述全球约10%的热带树种多样性的生长、死亡和补充的数据集。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的网络开发，并使用与调查和普查巴罗科罗拉多岛(BCI)50公顷森林动态图相同的方法建立，正如来自BCI样地的数据在我们理解在地方尺度上发生的生态过程的社区层面后果方面发挥了重要作用，我们将展示这些样地现在如何提供了一个前所未有的机会来检验热带生态学中的一个古老问题：土壤资源如何影响样地之间以及样地内不同生境类型之间观察到的森林结构和人口周转率的变化？为了实现这一目标，我们提出了三套测量方法。在九个样地上，我们将使用水文模型(TOPMODEL)来表征土壤水分有效性的变化。该模型基于降雨量、径流数据和当地地形来预测土壤水分饱和亏缺。第二，为了实现这一目标，我们提出了三套测量方法在目前缺乏土壤数据的五个地块中，我们将采样标准化的、地形定义的生境类型内的土壤化学性质。第三，在相同的地块中，我们将使用菌根和非菌根先锋物种进行苗木生长实验，以评估每种生境类型的土壤养分的植物有效性。这些测量将使我们能够在两个空间尺度上解决问题。在小区间尺度上，我们将能够询问茎密度和断面积，以及生长、死亡和补充的群落宽度与水分有效性和土壤肥力之间的关系。在小区内尺度上，我们将询问物种是否表现出特殊的表层水生态位，以及生境类型在土壤肥力、周转率、生境类型上是否存在差异解决这些广泛的问题，涉及土壤资源和植被特征之间的相关性，反过来将允许我们完善未来的假设，旨在了解物种间人口和分布差异的机制基础。这项研究将提供热带森林生长环境的第一个标准化的大规模测量。我们很少尝试跨洲方法来测试生态系统功能和群落组织的问题，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极限的理解，这将是至关重要的。了解水和养分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的多样性这对于预测未来植被对气候变化的反应至关重要，也将在指导管理以保护森林多样性方面迈出第一步。该项目成果的广泛传播和应用得到了国内合作者的积极参与和通过国家森林论坛共享数据的保证。

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.