Bruno Petriccione1 , Alessandro Bricca2
1) Carabinieri, Biodiversity and Park Protection Dpt. (Castel di Sangro Biodiversity Unit), via Sangro 45, Castel di Sangro (AQ), Italy. 2) University of Roma Tre, Science Dpt., V.le Marconi 446, Roma, Italy
Since 1986, vegetation monitoring of alpine plant communities has been performed at the Gran Sasso d’Italia LTER site (https://deims.org/c0738b00-854c-418f-8d4f-69b03486e9fd) in the Central Apennines, through phytosociological relevés and abundance and coverage estimation of the vascular flora at fine scale. The monitoring activities for abiotic parameters regard air and soil temperatures, rainfall, snowfall and snow cover persistence. A comparative analysis of changes in species composition, life forms, life strategies and morpho-functional types allowed recognition of dynamical processes (fluctuation and degeneration) and an increase in stress- and drought-tolerant and ruderal species, probably linked to a general process of climate change. A trend of variation forced by increasing drought was recorded in high-mountain plant communities, normally within a dynamic fluctuation process. There has been a 50–80% change in species composition with respect to the total number of species observed over the years. Whereas the total number of species has increased in all communities, in high-mountain mesic grassland 20% of sensitive species have completely disappeared. Early signs of a degeneration process were already discernible after seven years: such signs are more evident in snow-dependent communities, with a quantitative increase in more thermophilic and drought-tolerant species and a parallel decrease in more mesic, cryophilic and competitive species. In particular, the following phenomena have been recorded in high-mountain mesic grassland, in agreement with predicted or observed phenomena in other Alpine or Arctic areas: (a) coverage increase (or appearance) of ruderal and stress- and drought-tolerant species; (b) coverage decrease (or disappearance) of cryophilic, mesic and competitive species.
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.
The warming trend at global level is confirmed and reinforced by data related to the LTER site “Gran Sasso d’Italia”: the mean annual temperature has increased by 1.7 °C over the last 65 years, corresponding to an average increase per decade of +0.26 °C. This is more than double the same values at global level (+0.7 °C in the last 60 years and +0.1 °C per decade, IPCC 2014), and very near the forecasted increase of +2.0° C by the year 2100 (IPCC 2014). This exceptional warming in alpine areas, together with a decrease in total precipitation (as recognized for the Central Apennines as a whole, even if not significant at the site) and snowfall (significant at the site), an increase in climate inter-annual variability and extreme events, and a frequent lack of snow cover, are the combined drivers of the intense species turnover observed, occurring over the last 30 years in all the biocenoses studied, although more marked in snow-dependent communities. A quantitative increase in more thermophilic and stress- and drought-tolerant species and a parallel decrease in more mesic, cold adapted and competitive species have been clearly detected. These results confirm the preliminary assumptions provided in Petriccione (2012) for the first 18–25 years of observation at the same LTER site. Ecological indicators demonstrate that the key factor in the ecological changes of the alpine biocenoses studied is drought, associated with the combined action of temperature increase, precipitation decrease and lack of snow cover and precipitation. The two communities studied react in different ways to these abiotic drivers: (1) the Pediculari-Seslerietum dry grassland, highly resistant and well adapted to drought, frost and drastic temperature ranges, shows very slow or no changes over time (in accordance with the results of Frate et al. 2018); (2) the Luzulo-Festucetum mesic grass- 32 Bruno Petriccione & Alessandro Bricca / Nature Conservation 34: 9–39 (2019) land, with low resistance (increase in species richness and invaders) and not adapted to drought and soil frost, shows important and rapid changes, increasing cover values for species with ruderal and stress-tolerant strategies, and a parallel decline in the former dominant species, towards first signs of drought stress. The fluctuation stage typical of these primary alpine plant communities seems to be changing toward a dynamical tendency of degeneration, with an important disgregation of the community due to deterioration of the ecological connections: as in the Central Alps, this process can lead to an ecological vacuum or a disequilibrium state in the biocenoses (Cannone and Pignatti 2014). In conclusion, our results enable us to answer the four questions listed in the introduction: a) plant communities are significantly changing over time, more for mesic grassland and less for dry grassland; b) toward a disequilibrium state; c) species are responding in different ways, altering the intra-community ecological connections; d) there is a relationship between the changes in the features of the communities and the predicted and the observed changes in the temperature and precipitation regimes. Additional long-term observations over the next decades are, in any case, required to confirm the hypothesis of a cause-effect relationship between climate change and changes in plant communities and to exclude natural and unknown fluctuations. The combined monitoring of vegetation (composition and structure) and temperature at high elevation will provide updated data on the processes currently underway on the high summits of the Apennines and will guide the local in-situ policies to conserve the associated plant communities and threatened species.
Citation: Petriccione B, Bricca A (2018) Thirty years of ecological research at the Gran Sasso d’Italia LTER site: climate change in action. In: Mazzocchi MG, Capotondi L, Freppaz M, Lugliè A, Campanaro A (Eds) Italian Long-Term Ecological Research for understanding ecosystem diversity and functioning. Case studies from aquatic, terrestrial and transitional domains. Nature Conservation 34: 9–39. https://doi.org/10.3897/natureconservation.34.30218
Si ringraziano gli autori per aver potuto pubblicare questo estratto del loro studio.