Herbarium records in Arctic dwarf shrub dendrochronology: Methodological approach and perspectives

Abstract

Our work aims to investigate whether herbaria resources can be used for the extension of Arctic dwarf shrub chronologies. The current use of herbaria reaches far beyond their initially aims; among the new applications, phenology observations and conservation biology can be mentioned. However, to this date, no studies on the use of herbarium specimens for dendrochronological research have been published. Examples of perennial plants from herbarium sheets that could potentially be used for such studies are dwarf shrubs, samples of which often consist of whole specimens, including the root system, the root collar and branches. Here, we present a protocol for the selection and processing of historical material. Based on the collections from Kew and Copenhagen, which are among of the largest herbaria with Arctic plants, a database of 25 areas from the Atlantic sector of the Arctic was created. Material from the following most common species was collected: grey willow (Salix glauca L.), polar willow (Salix polaris Wahlenb.), dwarf willow (Salix herbacea L.), net-leaved willow (Salix reticulata L.), arctic willow (Salix arctica Pall.), mountain avens (Dryas octopetala L.), dwarf birch (Betula nana L.). We present the preliminary results of a case study using historical samples of Salix arctica from the Thule (Qaanaaq) area, NW Greenland. Dwarf shrubs can commonly reach the age of 80–100 years or beyond, while herbaria resources may allow the extension of such series over the last centuries. Therewith, these resources may provide an excellent proxy data source on the changing natural environment beyond the northern and upper tree limits, where well-replicated proxy time-series remain sparse.