Thirty years of ecological research at the Gran Sasso d’Italia LTER site: climate change in action

Study area The LTER site EU IT 01-003-T “Appennino Centrale: Gran Sasso d’Italia”, established in 1985, covers an area of ca. 0.5 km2 , with an elevation range from 2130 to 2385 m a.s.l. (approx. latitude 42°26N and longitude 13°33E, Suppl. material 1, Figure S1). The Gran Sasso d’Italia massif is located in the Central Apennines, which reach their highest elevation with the Gran Sasso peak (2914 m a.s.l.). The research site, one of the highest in Italy, has been a protected area both at National (as a National Park) and European level (as part of the EU Natura 2000 Network) since 1995. Land use in the site has remained unchanged over the last 50–100 years (personal observations, Falcucci et al. 2007): the only relevant activities are based on winter sports (a small ski resort is located at the southern boundary of the site), mountaineering and, more recently, nature tourism, all with very low impact on plant communities. In the past, land use was based on transhumant sheep farming, in progressive and rapid abandonment after the major political and economic change affecting Italy at the end of the 19th century (Clementi 1995). As a result, land management has not changed significantly, at least not since 1986, the year of ecological research at the site began. The climate is Mediterranean-mountain (Pignatti 1969, Petriccione 2005), with an average annual temperature of 3.7 °C, average annual precipitation of 1170 mm, maximum rainfall in spring and autumn, no drought period in summer, but an extreme and prolonged frost period in winter, for 5–6 months, with prolonged snow cover for more than 6 months a year. The average monthly maximum temperature is not very high (17.4 °C), whereas the average monthly minimum temperature is very low (- 8.9 °C). Since 1986, the same ecologists (first from the Universities of Rome and L’Aquila, from 1999 the Corpo Forestale dello Stato (National Forest Service) and since 2017 the Biodiversity and Park Protection Department of the Carabinieri) have been continuously studying the state of the high elevation vegetation, analysing all the plant species present in permanent plots where surveys are carried out once a year. Since 2013, the microclimate has also been studied directly using automatic temperature measurement devices installed in the soil. The site consists of high elevation plant communities above the timberline, in the central Mediterranean basin, along the Apennine mountain range, included in the alpine and Mediterranean high-mountain altitudinal belts (Petriccione and Persia 1995). They belong to two habitat types protected by EU Habitat Directive no. 92/43/EEC and listed in its Annex I (attribution to EU habitat types according to Biondi et al. 2009 and personal observations). Two biocenoses are studied in detail, both described by Petriccione and Persia (1995) and characterized by perennial species, particularly well adapted to cold and drought conditions, with high resistance, but very low resilience: (a) high-mountain primary dry grassland (Pediculari elegantis-Seslerietum tenuifoliae, corresponding to habitat “6170 – Alpine and subalpine calcareous grasslands” ), with non-continuous plant coverage, occurring between 2000 and 2300 m a.s.l. in the Central and Southern Apennines, in wind-swept peak and ridge zones with spatially limited and temporally discontinuous snow-cover, below zero night temperatures for ca. eight months a year and intensive cryo-nival phenomena (ice needles) in all seasons (except for the summer); soil is shallow (ca. 20 cm) and pH is basic (7.20–7.50, Furrer and Furnari 1960, Suppl. material 1, Figure S2); (b) high-mountain primary mesic grassland (Luzulo italicae-Festucetum macratherae, corresponding to the priority habitat “6230* – Species-rich Nardus grasslands, on siliceous substrates in mountain areas and submountain areas in Continental Europe”), with continuous plant coverage, occurring between 2000 and 2400 m a.s.l. throughout the Central Apennines, in wind-free zones with snow-cover for ca. six months a year, below zero night temperatures for ca. eight months a year and the absence of crio-nival phenomena (due to the prolonged snow-cover); soil is deep (cm 35–55 ca.) and pH is acid (4.50–5.90, Furrer and Furnari 1960, Suppl. material 1, Figure S3). The two plant communities are sampled on the basis of six permanent plots (three plots for each community), each measuring 100 m2 , grouped in two three-plot clusters, representative of a larger area of ca. 0.5 km2 . The site parameters observed include primary producers (species frequency and abundance, yearly) and microclimate (soil temperature, hourly, throughout the year). Some information on the microclimate characteristics of the Pediculari-Seslerietum community are already available for that specific site, although only for one summer season (Brucculeri and Petriccione 1994): the maximum recorded temperature is 27.5 °C.