Rereading a tree-ring database to illustrate depositional histories of subfossil trees

Late Quaternary tree-ring chronologies have been constructed using data collected from subfossil trees preserved under favourable conditions in lake sediments and peat deposits. Tree-ring widths and densities are commonly used for reconstructions of past climate variability. An alternative way of using these data is to explore the replication curves of these chronologies. Here, we make use of previously collected data that is currently available from tree-ring databases to demonstrate the depositional histories of pine trees once accumulated into the sediment in lake (i.e., riparian trees) and peatland sites. Divergent courses of depositional histories were obtained for different sedimentary settings in southern Finland. Accumulation of peatland pines was high, but that of riparian trees was low around 1.0 ka during the Medieval Climate Anomaly (MCA). By contrast, the accumulation of peatland pines declined towards the Little Ice Age (LIA), while that of riparian trees increased, with a culmination around 0.7 ka. We interpret these variations to mean transitional environmental changes in the corresponding habitats and to indicate increased precipitation and a rising water table from MCA towards the LIA. These results demonstrate the relative roles of recruitment and preservation potentials, and thus of palaeoecological and taphonomic processes, in controlling the tree accumulation in peatland and lake environments, respectively. We conclude that subfossil tree-ring chronologies, even those extracted from electronic databases, can provide important insights into palaeoecology, furnishing new perspectives on palaeoclimate, palaeohydrology of lakes and peatlands, and for studying the tree population responses to past climatic changes.