The influence of climate on pool inception in boreal fens

Abstract

Fens are one of the two most important peatland types of the boreal biome. The fen surface is often made of contrasted microenvironments, pools and strings, distributed in a geometric arrangement known as patterned fen. The fens are under the influence of varying water regimes causing the formation of pools, a process that we named aqualysis. The term refers to the physical degradation of the vegetation cover under the influence of water ponding. It is proposed here that pool inception is among a set of differential responses of peatland ecosystems to changes in hydrology caused by climate. In this study, we have evaluated the influence of climate on pool inception using the spatiotemporal distribution of trees found dead in pools of four boreal fens of northwestern Quebec. Tree-ring dating of tree mortality allowed the determination of the most recent and synchronized periods of pool formation in the studied fens. Most trees died over the last centuries, particularly after 1750 AD. The demographic pattern of tree establishment and mortality highlights a climatic forcing linked to the Little Ice Age oscillation opposing less humid events facilitating tree colonization succeeded by more humid events causing massive tree death and pool inception. We conclude that peatland aqualysis is among the processes controlled by climate contributing to the dynamics of patterned fens through pool formation.