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High mountain ecosystems and their biota are governed by low-temperature conditions and thus can be used as indicators for climate warming impacts on natural ecosystems, provided that long-term data exist. We used data from the largest alpine to nival permanent plot site in the Alps, established in the frame of the Global Observation Research Initiative in Alpine Environments (GLORIA) on Schrankogel in the Tyrolean Alps, Austria, in 1994, and resurveyed in 2004 and 2014. Vascular plant species richness per plot increased over the entire period, albeit to a lesser extent in the second decade, because disappearance events increased markedly in the latter period. Although presence/absence data could only marginally explain range shift dynamics, changes in species cover and plant community composition indicate an accelerating transformation towards a more warmth-demanding and more drought-adapted vegetation, which is strongest at the lowest, least rugged subsite. Divergent responses of vertical distribution groups of species suggest that direct warming effects, rather than competitive displacement, are the primary causes of the observed patterns. The continued decrease in cryophilic species could imply that trailing edge dynamics proceed more rapidly than successful colonisation, which would favour a period of accelerated species declines.

High mountain areas above the alpine zone are, despite the low-temperature conditions, inhabited by evolutionary and functionally differing organism groups. We compared the abundance and species richness of vascular plants, oribatid mites, springtails, spiders, and beetles, as well as bacterial and methanogenic archaeal prokaryotes (only abundance), at 100 m vertical intervals from 2,700-3,400 m in the Central Alps. We hypothesized that the less mobile microarthropods and microorganisms are more determined by and respond in similar ways to soil properties as do vascular plants. In contrast, we expected the more mobile surface-dwelling groups to forage also in places devoid of vegetation and thus to show patterns that deviate from that of vascular plants. Surprisingly, the observed patterns were diametrically opposed to our expectations: soil-living oribatid mites and springtails showed high individual numbers at high elevations, even where vascular plants barely occurred. Springtails also showed a rather constant species richness throughout the entire gradient. In contrast, patterns of surface-dwelling organisms and of archaeal prokaryotes did not differ significantly from vascular plants, because of either comparable climate sensitivity or their dependency on vegetated habitats. This study may serve as a baseline to estimate the risks of biodiversity losses in response to climate change across different biotic ecosystem components and to explore the potential and limitations of vascular plants as proxy for other organism groups that are far more challenging to monitor.

Areas of 2,800-3,000 m a.s.l. represent the alpine-nival ecotone in the Alps. This transition zone connecting the closed swards of the alpine belt and the scattered vegetation of the nival belt may show particularly strong climate warming driven fluctuations in plant species richness compared to the nival belt. To test this hypothesis, 12 summits within this range were investigated in the canton of Grisons, Switzerland in 2004. Complete lists of vascular plant species consisting of 5-70 species were collected on each summit and the elevation of the uppermost occurrence of each species was recorded. These data were compared to historical records over 120 years in age. Within this time, vascular plant species richness increased by 11% per decade on summits in the alpine-nival ecotone. Despite this considerable change, a comparison with nival summits did not support the hypothesis that species richness increase at the alpine-nival ecotone is higher than in the nival belt. A general trend of upward migration in the range of several metres per decade could be observed. Anemochorous species were more often found to be migrating than zoochorous or autochorous species and migration was higher on calcareous than on siliceous bedrock. A comparison between the summits with the adjacent slopes in our study revealed that changes in species number could be used as an indicator for climate-induced changes--if at all--only for the narrow summit areas.

The alpine–nival ecotone is the transition between the lower located alpine grassland/tundra zone and the upper located sparsely vegetated nival zone in the mountains. Its characteristics are qualitatively known. Here we study the dynamics of the ecotone through a quantitative approach based on plant data (from MtSchrankogel, 3497m, observations 1994 and 2004) and snow data (from 268 routine climate stations in the Alps, observations 1975–2004). We introduce the nivality index as the area ratio of nival and alpine plants, and the snow duration as the length of the summer snow cover. We fit a nonlinear probabilistic model to our field data; it yields state functions of both quantities. The nivality index curve comprises the entire information of the plant data in one analytical function; the snow duration curve represents the equivalent for the full snow data set. Thus all relevant parameters of both quantities follow from the respective state function. We find that the analytical profile of the alpine–nival ecotone at MtSchrankogel (based on nivality index observations from the altitude interval 2910–3090m) happens to sit right in the center of the independently determined summer snow profile across the entire Alps; specifically, the central altitude of the Schrankogel ecotone coincides almost perfectly with the central altitude of AlpineWe distinguish between the terms ‘Alpine’, which addresses the European Alps in a geographical/climatological context, and ‘alpine’, which describes a vegetation zone. snow duration. Both state functions show extreme temperature sensitivity at 2967m (vegetation) and 2897m (snow), and both altitudes exhibit a positive trend during the measurement period.