Paleosymmetry: tipping points and the dynamics of range contractions

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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.