Estimating Forest Productivity Over Regional and Multi-Decadal Time Scales Using Carbon Isotopes in Tree Rings

使用树木年轮中的碳同位素估算区域和数十年时间尺度的森林生产力

• 批准号: 1229887
• 负责人: Alan Taylor
• 金额: $ 20.56万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-08-15 至 2016-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1229887&HistoricalAwards=false
• 关键词: Estimating; Forest; Productivity; Over; Regional

Terrestrial ecosystems are a key component of the global carbon cycle and a better understanding of their role in carbon cycle dynamics is needed to project the future carbon cycle. Current ecosystem carbon cycle models give highly variable projections for the response of the terrestrial carbon cycle to changing climate. Constraining ecosystem carbon-budget projections is an important issue given the interest in managing forests to increase the strength of the carbon sink to mitigate anthropogenic carbon emissions. Spatially explicit data on forest ecosystem productivity and net carbon exchange between the forest and atmosphere that span multi-decadal to centennial time periods, are needed to constrain model parameters and to evaluate model performance. But, such records are sparse. Current observational and remotely sensed data are limited to the last few decades, and tree-ring width records have shown relatively poor correlation with contemporary net carbon flux measurements. In this research project, the investigators postulate that carbon isotopes in tree-rings represent a proxy of forest ecosystem productivity and net carbon exchange between forests and the atmosphere. This hypothesis is based on carbon isotope theory and carbon isotope measurements from tree rings located in the footprint of an eddy covariance carbon dioxide flux tower. This project will test two related hypotheses. The first is that carbon isotopes in tree rings provide a good estimate of forest productivity and net ecosystem carbon exchange. This will be determined by comparing isotope measurements from trees with measurements from nearby long-running eddy-covariance flux towers. The second hypothesis will investigate whether the temporal variability of the carbon isotope record in the tree ring records representing forest productivity and ecosystem exchange are coherent between two flux towers separated by several hundred kilometers. This will be determined by sampling tree rings at nine sites between two flux towers and analyzing the spatial coherence of the tree-ring isotope record and several other climate and forest productivity variables across the sites. If the hypotheses are supported, a network of ecosystem-specific records of forest ecosystem productivity and net carbon exchange could be established to parameterize the next generation of earth system and carbon cycle models. The science education impact of this project will extend beyond the university by developing learning modules for use in secondary schools that service underrepresented groups using an established NSF GK-12 project at Penn State.This project will determine if carbon isotopes in tree rings record the exchange of carbon dioxide between forests and the atmosphere. Contemporary forest-atmosphere exchange measurements are only available for approximately twenty years, making it difficult to test models used to project the carbon budget of forests and other ecosystems into the future and to determine their likely contribution to future climate change. This project will demonstrate the potential of using carbon isotopes in tree rings to estimate forest productivity and net carbon storage by forests over time periods of a century or more at local to regional scales. More accurate estimates of regional century-scale forest productivity and net carbon storage will inform climate and carbon management-related policy decisions regarding carbon sequestration efforts to mitigate anthropogenic carbon emissions.

陆地生态系统是全球碳循环的关键组成部分，需要更好地了解它们在碳循环动力学中的作用，以预测未来的碳循环。目前的生态系统碳循环模型对陆地碳循环对气候变化的响应给出了高度可变的预测。考虑到管理森林以增加碳汇强度以减少人为碳排放的利益，限制生态系统碳预算预测是一个重要问题。需要关于森林生态系统生产力和森林与大气之间的净碳交换的空间明确数据，这些数据跨越几十年至百年的时间周期，以约束模型参数和评估模型性能。但是，这样的记录很少。目前的观测和遥感数据仅限于过去几十年，树木年轮宽度记录与当代净碳通量测量结果的相关性相对较差。在本研究项目中，研究人员假设树木年轮中的碳同位素代表了森林生态系统生产力和森林与大气之间的净碳交换。这一假设是基于碳同位素理论和从位于涡流相关二氧化碳通量塔足迹的树木年轮中测量的碳同位素。这个项目将检验两个相关的假设。首先，树木年轮中的碳同位素提供了对森林生产力和生态系统净碳交换的良好估计。这将通过比较树木的同位素测量值与附近长期运行的涡旋协方差通量塔的测量值来确定。第二个假设将研究代表森林生产力和生态系统交换的树木年轮记录中碳同位素记录的时间变率在相隔数百公里的两个通量塔之间是否一致。这将通过在两个通量塔之间的9个地点取样树木年轮，并分析这些地点树木年轮同位素记录的空间一致性以及其他几个气候和森林生产力变量来确定。如果这些假设得到支持，则可以建立一个特定生态系统的森林生态系统生产力和净碳交换记录网络，以参数化下一代地球系统和碳循环模型。该项目的科学教育影响将扩展到大学之外，通过开发中学使用的学习模块，利用宾夕法尼亚州立大学已建立的NSF GK-12项目为代表性不足的群体提供服务。这个项目将确定树木年轮中的碳同位素是否记录了森林和大气之间的二氧化碳交换。当代森林-大气交换测量只能获得大约20年的时间，因此很难测试用于预测森林和其他生态系统未来碳收支的模型，并确定它们对未来气候变化的可能贡献。该项目将展示利用树木年轮中的碳同位素在一个世纪或更长时间内估算森林生产力和森林净碳储量的潜力。对区域百年尺度森林生产力和净碳储量的更准确估计，将为气候和碳管理相关的政策决策提供信息，这些政策涉及减少人为碳排放的固碳努力。