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Ecosystem reconstruction in the high mountains of Norway using dwarf shrubs for dendroecological analyses.

Bär, Annette*,1, 2, 3, 1 University of Oldenburg, Oldenburg, Germany2 University of Bonn, Bonn, Germany3 University of Bergen, Bergen, Norway

ABSTRACT- An interesting way to study changes in high mountain ecosystems is implemented by using a combined dendro-ecologic and micro-environmental approach. Study plots were defined at different scales along micro-topographic, altitudinal, and macroclimatic gradients. By mapping micro-environmental parameters like plant abundance, vegetation structure, root density and soil properties as skeleton fraction, and pH current ecosystem functioning is recorded. A time scale is complemented to the analysis by studying woody plants. There, growths determine factors in mountains like temperature, precipitation, and snow cover are recorded in annual tree rings which enable to study their impact and changes over time. Above tree line they are mainly represented by dwarf shrubs. The approach to use dwarf shrubs for dendro-ecological analyses is new and allows first attempts for such kind of reconstructions in high mountain ecosystems. By using different spatial scales within a hierarchical sample concept growth limiting factors can be determined which are representative for each scale. For that approach, three dwarf shrub species that exhibit clearly visible, countable and measurable annual growth rings and that occur along all studied transects were selected for dendroecological analysis: Empetrum hermaphroditum, Loiseleuria procumbens and Betula nana. The ages of the analysed individuals reaches up to 100 years. First results of measurements on Empetrum show that it is possible to use alpine dwarf shrubs for quantitative dendroecological analyses. However, several technical obstacles have to be overcome. In alpine regions, annual increments are in general very low and vary between 0.08 on summer warm, snow protected south facing slopes and 0.05 mm/yr on snow free ridges. In addition, eccentric piths, extremely asymmetric trunk geometry, and discontinuous rings cause severe problems for proper cross-dating of the ring width series. However, it is possible to synchronise individual growth curves and to construct site-specific ring width chronologies. For the ecological interpretation of the growth curves, local measurements of several climate parameters within the study sites are available. Concluding, dwarf shrubs can be used to reconstruct past climate and ecosystem changes.

Key words: Dendroecology, High Mountains, Dwarf shrubs

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