The findings, published in the journal Italian Botanist, come from repeated surveys of the same two-hectare patch of rock and scree, carried out in 1991, 2006 and 2021 and compared against Arietti’s original 1935 inventory. Because the peak is relatively isolated, ringed by ice and sheer cliffs, and because its flora was documented so carefully so long ago, it offers an unusually clean record of how climate change is reshaping life at the very top of Europe’s mountains.

The Alps have warmed by roughly 1.8 degrees Celsius since 1880, nearly double the global average, and climate models project an increase of more than 4 degrees by the end of this century for the southern Alps under a worst-case scenario. The area around Lobbia Alta is warming especially fast: measurements from the nearby Cima Presena weather station, at 3,015 metres, recorded average temperatures rising by 0.5 degrees per year between 1998 and 2008, and by 0.7 to 0.8 degrees per year when only summer months are considered.

Against that backdrop, the numbers tell a striking story. Between 1935 and 1991, the species count climbed from 17 to 36, with no losses, an entry rate of 0.34 species per year. From 1991 to 2006 the count rose to 45, with every species from the 1991 survey confirmed and the entry rate accelerating to 0.6 species per year — a figure consistent with the accelerating upward march of mountain plants documented across 302 European peaks in a landmark 2018 study. In the most recent interval, from 2006 to 2021, the total reached 51 confirmed species, with ten new arrivals offset by four that could no longer be found.

The newcomers are not simply more of the same. The biological composition of the summit flora has grown steadily more complex. Arietti recorded only hemicryptophytes and chamaephytes — perennial herbs and low cushion plants. By 1991 the first therophyte, the tiny annual eyebright Euphrasia minima, had appeared, along with the first dwarf shrub, the bog bilberry Vaccinium uliginosum subsp. microphyllum. Arietti had been categorical in 1936: shrubs were completely absent. By 2006, true woody plants had arrived in force, including common juniper, rusty-leaved alpenrose and the creeping dwarf willow Salix herbacea. And by 2021 the summit had gained its first true tree: a 35-centimetre-tall European larch, Larix decidua, growing at 3,130 metres.

That larch may be the most remarkable find of all. The previous highest known larch in the Alps stood at 2,995 metres in the French Alps, and historical references capped the species at around 2,660 metres. Only a single Swiss stone pine, a 1.1-metre specimen found at 3,200 metres on the Italian side of Monte Viso, exceeds the Lobbia Alta larch among recorded trees in the Alps and in Europe. In the Caucasus, by comparison, trees are not known to grow above about 3,100 metres. A seedling of the Swiss willow Salix helvetica, found at 3,111 metres, likewise sets a new high mark for its species.

Other records are no less striking. The frog orchid Coeloglossum viride, a circumboreal species found at 3,150 metres on Lobbia Alta, is probably the highest known orchid in Europe, including the Caucasus. The snow gentian Gentiana nivalis was found at 3,123 metres, just above the previous Alpine record of 3,110 metres in the Aosta Valley. Gentianella anisodonta, an endemic of the eastern Alps, was recorded at 3,145 metres, far above the 2,780 metres reported for the Swiss Grisons in the 1930s. And the endemic primrose Primula daonensis reached 3,151 metres, confirming an earlier record from the same peak and eclipsing a 1975 observation at 2,960 metres in Switzerland. In total, the researchers count six species that appear to set Alpine-level elevation records on this single summit, and roughly twenty species whose presence exceeded the maximum elevations listed in the standard reference flora for Trentino.

The ecological signature of the change is visible not just in species counts but in what the plants require. Using Ellenberg indicator values, which rate each species’ preference for warmth and soil nutrients on standard scales, the researchers tracked a steady rise in both the average temperature index and the nutrient index of the summit flora across the three surveys. The temperature index approached a value of 2 by 2021, driven by the arrival of more thermophilic, warmth-loving species, while the nutrient index climbed with the appearance of nitrophilous plants such as the spiny thistle Cirsium spinosissimum. In plain terms, the summit community is shifting toward species typical of warmer, more nutrient-rich conditions lower down the mountain.

How do plants reach a summit surrounded by ice and hostile cliffs? The researchers point to wind and birds as the main couriers. The larch’s winged seeds travel on the wind, while the seeds of the crowberry Empetrum hermaphroditum, another 2021 arrival, are dispersed by birds. Once seeds arrive, establishment depends on growing conditions — and here climate change is decisive. Longer snow-free periods at the summit give seedlings and saplings an increasingly long window in which to root and survive. The dark, cracked Tonalite outcrops of the south-facing slope, with their thin pockets of organic soil in crevices, appear to offer just enough shelter for newcomers from lower elevations to gain a foothold.

Yet the colonization is not a simple one-way march. Four species recorded in 2006 — Potentilla frigida, Rhododendron ferrugineum, Salix herbacea and Solidago virgaurea subsp. minuta — could not be found in 2021. The researchers interpret this as a trial-and-error process: on a peak above 3,000 metres, it is the recent arrivals that are most likely to vanish, while long-established species persist. That pattern carries a caution, however. Even the summit’s veteran plants, adapted to some of the harshest conditions in Europe, could ultimately be undermined by continued warming. The authors also raise a provocative hypothesis: that the southern Rhaetian Alps, on the moist southern slope of the mountain chain, may be experiencing a more intense upward influx of species than other Alpine regions, though they stress that further research is needed to test it. What is already clear is that a single granite peak, quietly watched by botanists for nearly a century, has become one of the most vivid documented cases of climate-driven change at the top of the Alps.

Subject of Research: Long-term change in the summit flora of a high Alpine peak in northern Italy under climate warming

Article Title: Changes in the flora of Lobbia Alta, a peak of the Adamello-Presanella Alps (Trento, Italy) between 1935 and 2021

Article References: Prosser, F., Bertolli, A., & Tomasi, G. (2023). Changes in the flora of Lobbia Alta, a peak of the Adamello-Presanella Alps (Trento, Italy) between 1935 and 2021. Italian Botanist, 15, 9-20. https://doi.org/10.3897/italianbotanist.15.97630

Image Credits: AI Generated

DOI: 10.3897/italianbotanist.15.97630

Keywords: Alps, climate change, elevation records, summit flora, Lobbia Alta, Adamello-Presanella, plant colonization, biodiversity monitoring, Ellenberg indicator values, European larch, orchid, Trentino