Dendroecology in the Arctic
Stef Weijers, Department of Geography, University of Bonn
In recent years dendrochronology and -ecology of (dwarf) shrubs has emerged as a new and promising scientific field, still largely unexplored. Retrospective growth analyses of woody dwarf shrub species can advance our knowledge of the impact of climate change on the arctic and alpine ecosystems of which they often form the backbone. In addition, growth chronologies of such species often exceed the length of local instrumental climate records in remote areas such as the high arctic. If so, annual growth parameters may serve as a climate proxy.
Here, the potential of shrub dendroecology is shown with the circumarctic evergreen dwarf shrub Arctic white heather, or Cassiope tetragona, as an example. Annual growth parameters of this species can be quantified as it forms smaller leaves at the beginning and end of each growing season resulting in wave-like patterns visible along its stems. After leaf removal, annual shoot length growth can be measured by summing the distances between two lows in leaf scar distances. Leaves and leaf scars are no longer present on older shoot parts, but the discovery of wintermarksepta (WMS), dark bands in the pith of C. tetragona stems coinciding with lows in leaf lengths and scar distances, has enabled the construction of growth chronologies of over 150 years in length. Climate-growth relationships for the species were tested at several sites in the High Arctic Archipelago of Svalbard, in northern Greenland, in northern Sweden, and in the Yukon through the construction of shoot length chronologies. In addition, field experiments were executed on the tundra in which temperature, precipitation, shading, and snow depth were manipulated.
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