Lakes cannot burn and buried charcoals cannot fly: Reconciling lake- versus soil-based reconstructions of past forest dynamics

Abstract

Fundamental understanding of paleoecological proxies is necessary when attempting to compare, complement, or contrast two or more methods, and lack thereof may lead to erroneous conclusions. This comment addresses three such misunderstandings found in a recently published paper by Paillard et al. regarding soil macrofossil charcoal analysis (SMCA) and its relationship to lacustrine sediment analysis. The aim is to correct some misinformation associated with the following three assertions: (1) Broadleaved tree species produce fewer charcoal fragments than coniferous species. Although coniferous stands are more fire-prone, experimental burning shows that species with denser wood, that is, broadleaves, produce greater amounts of charcoal under similar fire conditions. (2) Preservation of charcoal particles is poor at the referenced study site. Once buried in the mineral soil compartment, charcoal particles remain quite stable. As such, SMCA has revealed Late Pleistocene marginal stands of broadleaved species. (3) Underestimating the importance of range-edge dynamics on the results of SMCA reconstructions. SMCA offers a stand-scale historical reconstruction that has proven well-suited to study peripheral stands and to reflect the heterogeneity of a landscape mosaic. By attempting to reconcile the SMCA (in situ) and lake sediments (ex situ) narratives, Paillard et al. missed one key aspect of comparing complementary proxies: they show different aspects of the past.