Complex interactions between diversity, land use and carbon stocks in tropical landscapes

热带森林占据了陆地表面的12%，蕴藏着一半以上的陆地生物多样性，并拥有40%以上的陆地碳(C)。这些森林在全球范围内受到高度威胁，热带森林砍伐约占温室气体排放总量的10%。因此，这项发现赠款提案旨在促进对热带景观碳封存潜力的科学了解。基于我对全球变化生物学的兴趣，更具体地说，在土地利用、树木多样性和碳储存之间的相互作用方面，我对这项研究计划的长期目标是(1)进一步了解热带森林生物多样性和生态系统功能之间的功能关系，(2)在景观水平上评估多样性和碳储量保护之间的协同/权衡。为了实现我的目标，我建议结合三种不同的方法。首先，生态学家在过去20年里投入了大量的努力来记录和确定解释生物多样性和生态系统功能之间关系的机制。几篇综述论文和荟萃分析现在提供的证据表明，物种混合的群落水平表现往往高于它们的单一栽培同行的平均水平。然而，到目前为止，森林生态系统在这项研究工作中的代表性不足。为了解决这一差距，我于2001年在巴拿马中部的撒丁尼拉建立了一片试验性人工林，将生物多样性与生态系统功能之间的关系的研究带入了一个新的现实主义水平。这片种植了5000棵树的森林是研究树木多样性和碳循环之间复杂联系的最古老的试验场之一。在未来五年的研究计划中，我建议使用撒丁岛人工林的长期数据集，以进一步了解生物多样性与生态系统功能关系的潜在机制。在模型的基础上，我还将评估树木多样性对生态系统功能稳定性的重要性。我提议的研究活动的另一部分建立在我们关于困扰热带森林C储量估计的不确定因素来源的工作之上。我们的结果表明，森林更新的动态及其对C类股票的影响是不确定性的主要来源。对次生林中碳的准确估计需要非常密集的抽样，因为累积率取决于森林和干预类型和年龄，因此我建议建立一个数据库，汇编巴拿马次生林生物量的现有数据，并产生新的数据来填补现有的空白。该数据库将用于估计不同森林类型的森林生物量和碳随时间积累的速度。这一演替的时间顺序将根据过去的土地使用情况而定。该数据库将首先为巴拿马开发，但我希望它将扩大到包括整个拉丁美洲区域的数据。最后，我希望促进对复杂的植被类型马赛克在生物多样性和碳保护方面的理解。我们最近在巴拿马进行的小空间尺度的研究表明，在密度的调节下，树木多样性和森林生物量之间可能存在权衡。在这里，我建议在巴拿马东部与当地土著和殖民农民密切合作，在整个分水岭的层面上制定碳和生物多样性的基线，将土地使用历史和生物多样性对碳储量的影响分开。建模将提供关于未来可替代土地利用后果的信息，为社会生态系统的研究做出坚实的贡献。

Tropical forests occupy 12% of the terrestrial surface, harbour more than half of terrestrial diversity and hold over 40% of terrestrial carbon (C). These forests are highly threatened globally and deforestation in the tropics accounts for some 10% of total greenhouse gas emissions. This Discovery grant proposal therefore seeks to advance scientific knowledge of the C sequestration potential of tropical landscapes. Building on my interests in global change biology, more specifically, in the interactions between land use, tree diversity and C storage, my long-term objectives for this research program are (1) to further the understanding of the functional relationship between biodiversity and ecosystem function in tropical forests, and (2) to evaluate the synergies/tradeoffs between diversity and C stocks conservation at the landscape level. To meet my objectives I propose combining three different approaches. First, ecologists have invested substantial efforts over the past two decades to document and identify mechanisms explaining the relationship between biodiversity and ecosystem functioning. Several review papers and meta-analyses now provide evidence that community-level performance of species mixtures tends to be higher than the average of their monoculture counterparts. Forested ecosystems however have been under-represented in this research effort to date. To address this gap, I established, in 2001, an experimental planted forest in Sardinilla, central Panama, which brought the study of relationship between biodiversity and ecosystem function to a new level of realism. With > 5000 trees, this planted forest is one of the oldest experimental sites studying the intricate links between tree diversity and C cycling. In the coming five years of this research program, I propose to use the long term data set from the Sardinilla planted forest to further the understanding of the mechanisms underlying the biodiversity-ecosystem function relationship. Relying on modeling, I will also evaluate the importance of tree diversity for the stability of ecosystem functions. Another part of my proposed research activities builds on our work on the sources of uncertainties plaguing the estimates of tropical forest C stocks. Our results suggest that the dynamics of forest regrowth and its impact on C stocks is a major source of uncertainty. Accurate estimates of C in secondary forests demand exceedingly intensive sampling because accumulation rates depend upon both forests and intervention types and ages, I therefore propose to create a database compiling existing data on secondary forests biomass in Panama and generate new data to fill existing gaps. The data base will serve to estimate the rate of accumulation of forest biomass and C through time for different forest types. This chronosequence of succession will be informed by past land use. The database will be first developed for Panama, but I hope that it will grow to include data from the entire Latin American region. Finally, I hope to advance the understanding of complex mosaics of vegetation types with regard to biodiversity and C conservation. Work that we recently carried out at small-spatial scales in Panama suggests that there might be a tradeoff, mediated by density, between tree diversity and forest biomass. Here I propose to work in eastern Panama in close collaboration with local indigenous and colonist farmers to develop a baseline for C and biodiversity at the level of an entire watershed disentangling the effects of land use history and biodiversity on C stocks. Modeling will provide information on the consequences of alternative future land uses making a solid contribution to the study of social-ecological systems.