WEAVE: Climatic Controls of Tropical Rainforest Productivity

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理解是现实模拟当前和未来可能气候情景下TRF在全球碳预算中的作用的主要障碍。最近在哥斯达黎加实地工作的结果，得到了其他模型研究的支持，表明后热带雨林的树木生长在每年的基础上变化很大。这种变化与气候变量的简单年平均无关，因此假设是这些变量在次年尺度上相互作用的结果。为了确定这一主要生态系统反应的基础，将需要在生理学相关的时间尺度上结合控制观测和建模，这是本项目的目标。本研究将探讨四个中心假设：1)林分水平的森林生产力在不同年份之间有很大的差异。(2)年地上产量的变化受辐射和温度的次年变化的共同驱动，土壤湿度具有幕式限制。3)林分林分产量在林内地形梯度上存在显著差异。4)树种组成对后叶生物量的影响显著。为了评估森林水平的生产力及其与气候的关系，将测量树木生物量、细凋落物、细根和粗木屑的年生产量。研究地块将在哥斯达黎加La Selva生物站的老生长TRF的主要地形和地形梯度上复制。在研究样地的同时，还将确定不同功能类群树种对气候因子的中短期功能响应。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。根据这项工作开发的反应函数将在每月测量的一系列个体上进一步测试和校准。然后，这些功能响应将被用于参数化基于冠层碳增益和拦截辐射之间关系的自顶向下森林生产力模型。森林生产力的实证研究和森林水平过程模型的结果将有可能广泛适用于理解森林生产力的区域差异、预测对全球气候变化的响应以及管理受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.