RAPID: Is Carbon Starvation a Proximal Cause of Tree Mortality from Defoliation?

2015年，新英格兰南部爆发了一场严重的舞毒蛾疫情。到2018年，这次爆发导致数千英亩橡树林的树木大量死亡。自从这种入侵性昆虫在北美东部造成如此广泛的树木破坏和死亡以来，已经有30多年了。这一事件为解决生态学中的一个基本问题创造了一个稍纵即逝的机会：树木死亡的直接原因是什么？阔叶树在春天利用储存的淀粉和糖来长新叶。舞毒蛾吃树叶，限制了树木储存足够的糖和淀粉的能力，如果这些含量低于临界水平，树木就会死亡。在去年爆发期间，研究人员在橡树林中建立了一个地块网络，这些地块经历了不同程度和频率的舞毒蛾活动。如果他们行动迅速，从今年春天长出叶子之前经历了0到3年落叶的橡树上采集淀粉和糖，然后跟踪这些树到下一个生长季节，研究人员就可以确定饥饿是否直接导致树木死亡。更好地了解树木死亡的时间和原因将为森林和景观树木的管理提供信息。这项研究也将提供学生在回答科学问题和如何运用科学知识解决森林管理问题方面的训练。温带落叶乔木在春季利用储存的非结构性碳水化合物（NSC）来产生新的木质部和叶片。碳饥饿假说认为，当NSC储存耗尽时，二次生长和冲洗是不可能或不充分的，树木死亡。落叶，如舞毒蛾侵染期间发生的落叶，是测试碳饥饿假说的直接机制。这项研究将评估NSC水平与落叶频率和严重程度的关系，以确定是否存在一个关键的NSC阈值，低于该阈值树木就会死亡。研究人员将通过从已知落叶历史的橡树的茎和根中收集小的木材样本来取样NSCs。这项研究有可能提供对树木死亡事件的机制理解，并为科学家和决策者预测生态系统对全球变化的反应提供模型。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

A severe gypsy moth outbreak began in 2015 in southern New England. By 2018, this outbreak had caused dramatic death of trees across thousands of acres of oak forest. It has been more than thirty years since this invasive insect caused such extensive tree damage and death in eastern North America. This event has created a fleeting opportunity to address a fundamental question in ecology: what are the immediate causes of tree death? Hardwood trees draw on stored starches and sugars in the spring to produce new leaves. Gypsy moths eat leaves, limiting a tree's ability to store enough sugars and starches, and if these drop below a critical level, the tree can die. During last year's outbreak, the researchers established a network of plots in oak forests that had experienced differing severity and frequency of gypsy moth activity. If they act fast and sample starches and sugars from oak trees that have experienced defoliation for 0 to 3 years before they leaf-out this spring, then follow these trees through the next growing season, the researchers can determine if starvation directly causes tree death. Better understanding of the timing and causes of tree mortality will inform forest and landscape tree management. This research will also provide student training in answering science questions and how to apply scientific knowledge to solving forest management problems.Temperate deciduous trees draw on stores of non-structural carbohydrates (NSC) in the spring to produce new xylem and foliage. The carbon starvation hypothesis posits that when NSC stores become depleted, secondary growth and flushing is impossible or inadequate, and the tree dies. Defoliation, such as occurs during gypsy moth infestations, is a straightforward mechanism for testing the carbon starvation hypothesis. This study will evaluate NSC levels in relationship to defoliation frequency and severity to determine if there is a critical NSC threshold below which tree mortality occurs. The researchers will sample NSCs by collecting small wood samples from the stem and root of oak trees with known defoliation histories. This study has the potential to offer a mechanistic understanding of tree mortality events and inform the models scientists and policy-makers rely on to forecast ecosystem responses to global change.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.