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

点击翻译按钮获取中文摘要

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.