WEAVE: Climatic Controls of Tropical Rainforest Productivity

9629245 Oberbauer热带雨林（IRF）是世界上最具生产力的陆地生态系统，是全球碳预算的主要组成部分。缺乏对气候和TRF生产力之间关系的全面了解是现实地模拟TRF在当前和未来可能的气候情景下在全球碳预算中的作用的主要障碍。最近在哥斯达黎加进行的实地工作的结果，得到其他模拟研究的支持，表明扶轮基金会的树木生长每年都有很大的变化。这种变化与气候变量的简单年平均值无关，因此假设是这些变量在次年度尺度上相互作用的结果。为了确定这一重大生态系统响应的基础，将需要在生理相关的时间尺度上结合受控观测和建模，这是本项目的目标。 本研究将探讨四个主要假设：1）扶轮基金会森林一级的生产力在不同年份之间有很大的差异。 2)年地上生产量的变化是由辐射和温度的年际变化的综合影响，与情节土壤水分限制。 3)林分生产量在森林研究基金会内沿林内土壤梯度沿着变化很大。 4)TRF生产力受物种组成变化的显著影响。 为了评估森林一级的生产力及其与气候的关系，将测量树木生物量、细凋落物、细根和粗木残体的年产量。研究地块将在哥斯达黎加的拉塞尔瓦生物站古老的森林资源基金的主要地形和土壤梯度上复制。在平行的地块，树木功能对气候因素的反应，将确定在短期和中期尺度的树种从不同的功能组。短期研究将用于评估整棵树的性能与当地小气候之间的关系。从这项工作中开发的响应函数将进一步测试和校准的一系列个人每月测量。这些功能的反应，然后将用于参数化的自上而下的森林生产力模型，冠层碳增益和截获的辐射之间的关系的基础上。 森林生产力的经验研究和森林水平过程模型的结果，将有可能广泛的适用性，了解TRF生产力的区域变化，预测对全球气候变化的反应，并为管理人类影响的热带生态系统。

9629245 Oberbauer Tropical rain forests (IRF), the worlds most productive terrestrial ecosystems, are a major component of the global carbon budget. The lack of a comprehensive understanding of the relation between climate and TRF productivity is a major impediment for realistically modeling the role of TRF in global carbon budgets under current and possible future climate scenarios. Recent results from fie1d work in Costa Rica, supported by other modeling studies, show that tree growth in TRF varies significantly on a year-to-year basis. This variation is not related to simple annual averages of climatic variables, and is therefore hypothesized to result from the interaction of these variables on a sub-annual scale. To determine the basis for this major ecosystem response will require a combination of controlled observations and modeling at physiologically relevant time scales, which is the goal of this project. This research will address four central hypotheses: 1) Forest-level productivity in TRF varies substantially among years. 2) Variation in annual aboveground production is driven by the combined effects of subannual variation in radiation and temperature, with episodic soil moisture limitation. 3) Stand-level production in TRF varies significantly along within-forest edaphic gradients. 4) TRF productivity is significantly affected by variation in speeies composition. To assess forest-level productivity and its relation to climate, annual production of tree biomass, fine litter, fine roots, and coarse wood debris will be measured. The study-plots will be replicated across the main topographic and edaphic gradients present in the old-growth TRF at the La Selva Biological Station in Costa Rica. In parallel with the plots, tree functional responses to climatic factors will be determined at short and medium time scales for species of trees from different functional groups. Short-term studies will be used to assess the relation between whole-tree performance and local microclimate. Th e response functions developed from this work will be further tested and calibrated on a series of individuals measured monthly. These functional responses will then be used to parameterize a top down model of forest productivity, based on the relationship between canopy carbon gain and intercepted radiation. Results of both the empirical studies of forest productivity and the forest-level process model, will potentially have wide applicability for understanding regional variations in TRF productivity, predicting responses to global climatic change, and for managing human-influenced tropical ecosystems.