Climate variability and growth competition in an arctic-alpine ecosystem: retrospective growth analyses of one deciduous and one evergreen dwarf shrub in the Norwegian Scandes

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Alpine ecosystems are regarded as vulnerable to climate change. Species evolved under specific harsh conditions might lose their competitive ability under warming conditions, resulting in range shifts in the species distribution, structural alterations of alpine ecosystems, and in certain areas, ultimately, a replacement of species currently growing in the upper alpine belts with those from the lower alpine belts. Retrospective growth analyses support predictions of the fate of alpine ecosystems under future global warming. In the upper alpine belts woody dwarf shrubs species form the backbone of the ecosystem. As trees, such shrubs form annual growth rings, and in recent years dendroecology of (dwarf) shrubs has emerged as a new and promising scientific field. Here, we aim to analyze the timing of growth of, climate-growth interactions in, and competition between two species, one deciduous and one evergreen, as example of a characteristic low alpine ridge site in the Norwegian Scandes. This will be done through the construction of ring-width chronologies (one for each species) and the statistical comparison of these growth time-series with both a unique, long-term, site specific, micro-climatic record and the regional climate record. By studying the species response to past and ongoing climate variability through retrospective growth analyses, the susceptibility of the species to their local climate envelope and the influence of climate variability on their competition will be revealed. This way, their future growth response to modified climatic site conditions can be quantified and our understanding of the vulnerability of arctic-alpine ecosystems to climate change will increase.