Paleosymmetry: tipping points and the dynamics of range contractions

复杂的系统，如气候、社会和陆地生态系统，可能会从一个州突然变化到另一个州。这些突变的开始被称为临界点或临界点。人们对找到方法来衡量和预测这些临界点非常感兴趣，以便预测何时会发生临界点，或者系统是否处于临界点的过程中。理解临界点的性质以及如何识别它们的一种方法是研究过去发生的那些临界点。在最近为古生态学家汇编的50个优先问题中，有两个问题涉及研究过去的临界点的必要性。这项提议的主要目的之一是首次将花粉粒对称性的变化作为气候和植被变化的临界点的衡量标准。第二个目的是了解气候和火在加拿大西北部的黑云杉和魁北克的白松北部分布界限的撤退中的共同作用。

Complex systems such as climate, societies, and terrestrial ecosystems may change abruptly from one state to another. The start of these abrupt transitions is termed the threshold or tipping point. There is enormous interest in finding ways by which we can measure and anticipate these tipping points in order to predict when one will occur or if the system is in the process of tipping. One approach to understanding the nature of tipping points and how they might be identified is to study those that occurred in the past. In a recent compilation of 50 priority questions for paleoecologists, two questions concerned the need to study past tipping points. One of the primary aims of this proposal is to apply, for the first time, changes in the symmetry of pollen grains as a measure of tipping points in climate and vegetation change. The second aim is to understand the joint roles of climate and fire in the retreat of the northern distributional limit of black and white spruce in NW Canada and white pine in Quebec.