Collaborative Research: Mechanisms of tree population collapses in eastern North America: Disentangling causes of abrupt ecological change during the Holocene

合作研究：北美东部树木种群崩溃的机制：解开全新世生态突变的原因

• 批准号: 1856047
• 负责人: Bryan Shuman
• 金额: $ 20.99万
• 依托单位: University of Wyoming
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-06-01 至 2024-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1856047&HistoricalAwards=false
• 关键词: Collaborative; Research; Mechanisms; tree; population

Trees are dying at alarming rates worldwide, raising concerns about forest health in the face of increasing droughts and fires. In the US, eastern forests have been less affected by droughts and fires than western forests. However, several eastern tree species -- notably eastern hemlock and American beech -- have experienced big population collapses over the last several thousand years. Hence, eastern forests may be at greater risk of collapse than commonly thought. This project will collect new data and apply powerful mathematical tools to test hypotheses about why hemlock and beech forests have suffered big declines. Researchers will focus on the roles of severe droughts, bigger and more frequent fires, and greater competition among tree species. Ultimately, this project seeks to 1) better understand the fundamental processes that trigger abrupt collapse of tree populations and 2) thereby inform and reduce current risks to forest health.The project will analyze long-term records (6,000 years, at decadal resolution) of forest composition, fire regime, and drought, based on lake sediment cores to be collected at four sites -- two at places where beech and hemlock are abundant today and two where only beech is abundant. At each site, the timing of past tree population declines will be established by records of fossil pollen and radiocarbon dates, while past fire events will be identified through analysis of the abundance of charcoal fragments in sediments. Because plant water stress affects the kinds of carbon isotopes in plant tissue, this project will identify past drought episodes through an innovative approach that requires precise measurements of the carbon isotopic content of individual pollen grains. Because all records will be co-located from the same sediment cores, the relative sequence of events will be precisely known. At two sites, reconstructions of changes in lake water balance, based on characteristics of the lake sediments, will provide an independent check on the drought and water-stress signals inferred from carbon isotopes. A new community-level statistical model will integrate data and be used to test hypotheses about the relative importance of drought, fire events, and competition on past declines of tree populations. All data collected will be archived in the Neotoma Paleoecology Database, an open public repository of long ecological records, curated by experts. All source code for statistical software developed here will be made publicly available, and a workshop will be held to train students and early career scientists in the new methods that will be developed.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

世界各地的树木正在以惊人的速度死亡，面对日益严重的干旱和火灾，引发了人们对森林健康的担忧。在美国，东部森林受干旱和火灾的影响比西部森林要小。然而，一些东部树种——尤其是东部铁杉和美国山毛榉——在过去几千年中经历了种群数量的大幅下降。 因此，东部森林崩溃的风险可能比人们普遍认为的更大。 该项目将收集新数据并应用强大的数学工具来检验有关铁杉和山毛榉森林为何大幅减少的假设。研究人员将重点关注严重干旱、规模更大、更频繁的火灾以及树种之间更激烈的竞争所扮演的角色。 最终，该项目旨在 1) 更好地了解引发树木种群突然崩溃的基本过程，2) 从而了解和减少当前对森林健康的风险。该项目将根据在四个地点收集的湖泊沉积物核心来分析森林组成、火灾状况和干旱的长期记录（6,000 年，以十年为单位）——两个地点位于当今山毛榉和铁杉丰富的地方，两个地点仅盛产山毛榉。 在每个地点，过去树木数量下降的时间将通过化石花粉和放射性碳日期的记录来确定，而过去的火灾事件将通过分析沉积物中木炭碎片的丰度来确定。 由于植物水分胁迫会影响植物组织中碳同位素的种类，因此该项目将通过一种创新方法来识别过去的干旱事件，该方法需要精确测量单个花粉粒的碳同位素含量。 由于所有记录都来自相同的沉积岩芯，因此可以准确地了解事件的相对顺序。 在两个地点，根据湖泊沉积物的特征重建湖泊水平衡的变化，将为从碳同位素推断的干旱和缺水信号提供独立的检查。 一个新的社区级统计模型将整合数据，并用于检验有关干旱、火灾事件和竞争对过去树木种群数量下降的相对重要性的假设。 收集到的所有数据都将存档在 Neotoma 古生态数据库中，这是一个由专家管理的长期生态记录的开放公共存储库。 这里开发的统计软件的所有源代码都将公开，并将举办一个研讨会，以培训学生和早期职业科学家使用即将开发的新方法。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。