Longues séries dendrochronologiques établies à partir de troncs subfossiles

Long tree-ring chronologies are often used in paleoecological and paleoclimatic reconstructions. However, in some regions of the World, such as Eastern North America, these chronologies are scarce. One objective of the ARCHIVES project was to develop a network of long tree-ring chronologies using black spruce subfossil logs collected in six lakes of the Quebec boreal forest. A large number of the sampled logs (1832 specimens) were successfully crossdated, which allowed the development of six long tree-ring chronologies spanning at least 1238 years. At the local scale, these chronologies show the influence of past wildfires on subfossil log recruitment in the lakes and on riparian forest growth. Furthermore, these chronologies are strongly correlated with observed July-August mean temperatures during the last century. These local chronologies were thus used to reconstruct past summer temperatures in the region. A well-expressed Medieval Warm Period (around AD 910-1250), which was warmer than recent conditions, was followed by the Little Ice Age (around AD 1300-1900) and by recent warming. The coldest decades of the last millennium, corresponding to the lowest riparian forest growth, were observed after the strong Kuwae and Tambora volcanic eruptions in AD 1452 and 1815, respectively.