Transitions and thresholds in global ecological changes of forest ecosystems

全球生态变化正在对森林生态系统产生意想不到的影响，人们对各种人为应激源(如气候变化)如何与自然干扰机制相互作用的了解在很大程度上是未知的。这部分是由于经验分析不足，部分是因为对门槛行为的建模不足。我们从经验和模型的角度考察了各种影响--从个人到群体再到景观。主要目标是提高我们对空间和时间动态的理解，包括在面临压力和干扰时预测树木、树木种群和森林动态的“关键”转变。我们研究计划的一个目标是检查树木(主要是树干年代学)和森林(通过古孢粉)数据，并使用现有的和新的分析(统计)工具来探索‘预警系统’，以帮助检测关键和非关键的过渡。另一方面，我们将在种群和生态系统层面建立基于过程的模型，以帮助更好地理解一些新情景下的这些转变，密切关注最近发现的树木的阈值行为。在将可用于检测关键过渡的统计工具与基于流程的模型联系起来方面，几乎没有做过什么工作，这突出了我们工作的新颖性。更紧密地结合经验和理论方法来了解胁迫和干扰对森林动态的影响，将推动生态学领域的发展，提高我们对森林生态系统的基本理解，并为管理决策提供信息。我们的研究将有助于确定在哪些条件下会发生突然变化，以及这些变化是否“关键”，可能有助于为未来生态系统响应中的意外情况做好准备或避免。尽管新的实地研究将重点放在加拿大和巴西，但这些发现将适用于世界各地，因为理论、统计和建模方法更一般，可以很容易地适应当地的研究/物种。

Global ecological changes are having unexpected effects on forest ecosystems and understanding of how various human-induced stressors (e.g., climate change) interact with natural disturbance regimes is largely unknown. This is partly due to insufficient empirical analysis and partly due to insufficient modeling of threshold behavior. We examine a variety of effects -– at scales from individuals to populations to landscapes -– from both empirical and modeling perspectives. The main objective is to improve our understanding of spatial and temporal dynamics, including predicting “critical” transitions in tree, tree population and forest dynamics in the face of stress and disturbances. One objective of our research program is to examine tree (largely dendrochronological) and forest (through paleopollen) data and explore ‘early-warning systems' using both established and new analytical (statistical) tools to help detect transitions, both critical and non-critical. On the other hand we will build process-based models at the population and ecosystem level to help better understand these transitions under a number of new scenarios, paying close attention to recently discovered threshold behaviour of trees. Little work has been done to link statistical tools available to detect critical transitions with process-based models which highlights the novelty of our work. A closer integration of empirical and theoretical approaches to understanding stress and disturbance effects on forest dynamics will advance the field of ecology, improve our fundamental understanding of forest ecosystems and inform management decisions. Our studies, which will help to determine under which conditions abrupt changes occur, and whether or not they are ‘critical', could help to prepare for or avert future surprises in ecosystem response. Though the new field studies will focus on Canada and Brazil, discoveries will be applicable worldwide because the theoretical, statistical and modelling approaches are more general and can be easily adapted to local studies/species.**