Dynamics of high-altitude environments as a life-support system to wild herbivores: carbon and moisture cycling, biodiversity and landscape modification - Gran Paradiso National Park
Lead Authors: CNR - IGG: A. Provenzale, I. Baneschi, S. Giamberini, S. Imperio, M. Magnani, P. Mosca, B. Raco
Contributors: PNGP: Bruno Bassano, Ramona Viterbi; CNR - IIA: Palma Blonda, Maria Patrizia Adamo, Cristina Tarantino; CNR- IRET: Andrea Scartazza, Daniela Di Baccio, Beatrice Pezzarossa, Roberto Pini, Irene Rosellini, Carlo Calfapietra.
High-altitude Alpine areas above the treeline are home to extremely rich biodiversity, associated with rare and/or endemic species adapted to extreme environments as well as with centuries of interaction and co-adaptation with human communities that transformed the mountain environment.
Figure 1 - Chamois in Gran Paradiso National Park. (c) AP
In the Gran Paradiso National Park (GPNP, www.pngp.it), large mountain ungulates, such as the Alpine ibex (Capra ibex) and Alpine chamois (Rupicapra rupicapra), rely on high-elevation grasslands to forage during spring-summer, to face the effort of reproduction and to gain weight before winter (Grignolio et al. 2003, Darmon et al. 2012). Mountain grasslands are semi-natural habitats, whose characteristics partly derive from agro/pastoral activities. The progressive abandonment of management practices such as mowing and grazing from high-elevation mountain areas caused modifications to grasslands that can affect their forage value for wild mountain herbivores (Parolo et al. 2011). In addition to a shift in plant species, changes in terms of species richness can also be observed: abandoned sites induced fundamental changes in ecosystem structure and functioning and a pronounced decrease in species diversity with respect to extensively used meadows, particularly on potential forest sites where tree growth leads to the suppression of many heliophilous species (Tasser and Tappeiner 2002; Tasser et al., 2005). Moreover, fragmentation of semi-natural grasslands due to increase of forests and woodlands may negatively influence the interchange of grassland species, leading to an increase in the number of non-typical grassland species in the meadows (Berlin et al. 2000).
Abandonment of traditional land management may also affect nitrogen plant concentration and mineralization (Zeller et al. 2000; Robson et al., 2010; Szukics et al., 2019), soil organic carbon fraction (Guidi et al. 2014; Garcia-Pausas et al., 2017) and the net ecosystem CO2 and CH4 exchange (Wohlfahrt et al. 2008, Imer et al., 2013; Ingrisch et al., 2017).
Climate change is another risk factor for mountain grasslands and their support role for large herbivores. An upward shift of Alpine plant species, and the associated community composition changes, has been observed on Alpine summits (Walther et al. 2005). In the next decades, a strong decline (or local extinction) of specialized montane plant species can be expected (Bruelheide 2003), particularly if joint effects of climate and land use changes are considered (Dirnbck et al. 2003). In addition, increasing temperatures can lead to higher evapotranspiration rates (Abtew and Melesse 2012), with direct consequences on soil moisture and vegetation structure. The decline of soil water availability induces an increasing reduction of nutrient uptake and carbon assimilation with a consequent slowdown in plant growth (Daly et al. 2004). Changes in the snowfall/precipitation regimes can modify the water content available for vegetation, affecting quantity and quality of forage for large herbivores. It has been demonstrated that the frequency of rainfall events may affect the net carbon assimilation and species productivity more than the total rainfall amount during the growing season (Fay et al. 2003). Indeed, the reduction in snow cover alters the frequency of soil frost events and the dynamics of freeze-thaw cycles. This could influence a range of ecosystem properties, including rates of nutrient cycling and, hence, the C trace gas (i.e. CO2 and CH4, Merbold et al., 2013; Wu et al., 2014).
Water and carbon fluxes between soil, vegetation and atmosphere are only partially known for mountain grasslands, also owing to the complex geological matrix, to the wide variations in soil depth and sub-soil characteristics (e.g., solid rock, fractured rocks, coarse moraine material, etc), and to the unknown response of the fluxes to climate variability.
In addition, the population dynamics of mountain ungulates is strictly related to seasonality (Jacobson et al. 2004). In the Gran Paradiso National Park, the winter snow cover decreased in the last three decades, both in terms of average depth and duration of the period during which the ground is covered with snow (Terzago et al. 2017). Possibly as a result of the earlier snowmelt and higher temperatures, the start of the growing season for Alpine grasslands appeared to happen earlier and earlier during the last 30 years. This change can be one of the reasons for the reduction of the Alpine ibex population observed from the mid '90s (Mignatti et al. 2012).
Other stressors, such as human disturbance/pollution through tourist activities, can exacerbate the impoverishment and reduction of this unique ecosystem. Off-trail hiking and mountain biking, for instance, may lead to a reduction in vegetation height, cover and species richness, as well as changes in species composition and increases in litter and soil compaction (Pickering et al. 2011).
The aim of this activity is to quantify the health status of mountain grasslands, using different study sites in the Gran Paradiso National Park (GPNP, Italy). Two sites are active since a few years, namely the Nivolet Plain and Noaschetta valley. In 2018, a third study site has been selected in Val di Nel, a glacial valley at 2700 m asl. The Nel site is devoted to the study of deglaciation and soil formation, in addition to the study of high-altitude alpine grasslands dynamics. These three sites show different characteristics, due to their different altitude and geomorphology, and are all exposed to the effects of direct human disturbance and climate-induced modifications. The three sites constitute the nucleus of a "Critical Zone Observatory" to be permanently established in the Gran Paradiso National Park, with the aim to study the processes happening in the heterogeneous environment at the Earth surface that goes from the bedrock to the top of the vegetation canopy (the "Critical Zone") where chemical, physical, geological and biological processes interact with each other, involving all environmental matrices such as rock, soils, water, air and living organisms. In fact, water, carbon and energy cycles are tightly coupled with each other and determine exchanges of matter and energy throughout the Critical Zone layer.
Figure 2: the Orco and Nivolet valleys in Gran Paradiso National Park. The three study sites are shown: Nivolet (top left), Piani di Nel (bottom left), Noaschetta (bottom right).
A preliminary study for assessing changes in land cover of Alpine grasslands in GPNP from Remote Sensing data has been pursued by comparing land cover from Copernicus layers in 2012 with recent Sentinel 2 data: an analysis of the percentage of land cover change vs altitudinal gradient showed that the greatest changes occur at an altitude going from 2,200 to 2,700 metres asl, which corresponds to elevations that range from the forest - grassland ecotone to Alpine meadows.
Figure 3. Remote-Sensing based detection of changes in the GPNP grasslands.
At present, human abandonment in Noaschetta (about 1,600 m above the sea level) leads to tree encroachment with species of low forage value (such as dwarf willows Salix sp.,) and the Park has started a programme of controlled cow grazing. The Nivolet plain is above the treeline (2,600 m asl) but still pastoral activities are present during the short summer period (July - September). Nivolet is home to wild ungulates and the health of the wild meadows can be affected by climate change and, especially in the Dora valley, by human presence and cow grazing.
In the Noaschetta Valley, the specific research question is focussed on the evolution of the managed and non-managed portions of the meadows. Several plots in the valley at different altitudes are monitored by the researchers of GPNP who mainly monitor the biodiversity of soil invertebrates outside and inside areas where cow grazing is either permitted (outside) or excluded (inside) (see also M4 Storyline), to analyse whether and how grazing influences soil and vegetation characteristics in the long term, including CO2 fluxes (both respiration and Net Ecosystem Exchange, NEE) from soil. NEE is the total CO2 flux that occurs between soil, vegetation and atmosphere and it is given by the difference between the CO2 absorbed by vegetation due to photosynthesis (constituting the Gross Primary Production, GPP) and the CO2 emitted by respiration of plants and soil (Ecosystem Respiration, ER). This activity is also part of the Long Term Ecological Research conducted at Gran Paradiso National Park, which contributes to the European eLTER network (see the Gran Paradiso National Park page on DEIMS: https://deims.org/e33c983a-19ad-4f40-a6fd-1210ee0b3a4b).
At Nivolet Plain, the specific research question is to analyse how carbon fluxes are controlled by meteo-climatic variables (radiation, air temperature, soil humidity and temperature, precipitation) as well as to the different soil and geological features present in the valley, using the experimental measurements in statistical analyses and in the validation of numerical simulations. To this end, four study plots have been selected in Nivolet plain, on the basis of the main geological and geomorphological features of the area: one lies on a gneiss substrate, one on carbonate rocks, one on an alluvial plain and the last one on a glacial deposit.
CO2 fluxes at the soil-atmosphere interface (both respiration and net ecosystem CO2 exchange) have been measured by a portable flux chamber in several campaigns during the vegetative seasons of 2017 and 2018 at all four sites, together with meteo-climatic and soil parameters. Moreover, two nearby weather stations provide daily records of temperature, precipitation and snow cover since more than 50 years.
At the Nivolet plain, the vegetative season usually starts in mid/late June, depending on the snow cover, and it ends in late August. At the beginning of September, only a few plant species still show some photosynthetic activity and also respiration declines (Figure 4).
Figure 4: Average values of NEE and ER for the gneiss plot, for the 9 campaign dates in 2017 and 2018. Errors bars are 1 standard deviation from the ensemble of the individual measurements on each measurement date and plot.
Statistical analysis of the results allowed for determining the dependence of Ecosystem Respiration and Gross Primary Production from on parameters such as soil temperature, humidity or radiation. Figure 5 shows, as an example, the dependence of ER on soil temperature for the carbonate plot.
Figure 5: ER versus soil temperature for the 2017 and 2018 campaigns, for the carbonate plot. The curve is the standard fit ER=ER0 Q0 [(T-T0)/T0].
When the overall NEE is negative, the grassland acts as a carbon sink. When it is positive, it releases carbon dioxide to the atmosphere. In the middle of the growing season, GPP prevails and the overall NEE is negative. This is when carbon dioxide is taken from the atmosphere and stored into plant leaves and roots. At the end of the growing season, not only the photosynthesis ceases but also respiration slows down, so the NEE, which is the balance between the two, approaches zero and it can fluctuate between small positive and negative values. The overall annual balance (is the grassland a source or sink of carbon dioxide?) depends on the complex influence of all meteo-climatic factors over vegetation physiology and biochemical reactions in soil.
In addition to the flux measurements, the excavation of soil pits at different plots (Figure 7) allowed to determine the soil profile and to collect samples at Nivolet and Nel for further physical-chemical characterisation in the lab (Soil Survey Staff, 1993). This information, together with the quantification and characterisation of above- and below-ground soil tissue, allowed to determine biometrical, physical, geochemical, biochemical and physiological properties of the different ecosystem components.
Figure 6: Soil profile from Glacial deposit (left) and gneiss site (right) at the Nivolet Plain.
The nutritional status of the meadows was evaluated analysing the micro- and macro-nutrient concentrations in both plant and soil components. The dynamics of Carbon (C) and Nitrogen (N) cycles were studied combining the analyses of C and N content and stable isotopes composition (δ13C and δ15N) in plant organs (shoots and roots) and soil organic matter (SOM). Photosynthetic pigments (chlorophyll and carotenoids) and leaf δ13C revealed differences in photosynthetic efficiency between the different sites. In the four meadows, a vegetational analysis has been performed, identifying representative target species as potential bioindicators of ecosystems functioning and of their response to climate conditions and environmental biodiversity. Preliminary results showed different behaviour of the same plant species depending on the soil substrate. Integrated analyses of plant-soil relationships in Alpine ecosystems represents a powerful tool to evaluate changes in the health status and ecosystem functioning of high-altitude environments.
Figure 7. Illustration of the flux chamber method used for measuring NEE (left) and respiration (right). (c) SG
At all sites, CO2 fluxes have been measured with a flux chamber method. The flux chamber is a portable instrument based on spectrophotometry, that allows to measure the fluxes of water vapour, carbon dioxide, methane and other constituents and gases at the interface between soil and atmosphere, depending on the sensors installed, both in presence of light, when photosynthesis is active, and in dark condition, when only respiration is active (see Figures 7 and 8).
Figure 8. Unexpected visitors at the flux measurement site. (c) SG
In summer 2019, an Eddy Covariance tower will be installed in one of the high-altitude grasslands of GPNP, equipped for measuring water and carbon dioxide fluxes. Isotopic carbon analysis of CO2 and CH4 will help reconstructing the carbon allocation in the soil and the redox processes which occur in the soil and at the soil-atmosphere interface.
Figure 9. A bird's view of Nivolet Plain. (c) AP.
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ECOPOTENTIAL related presentations and publications:
Ilaria Baneschi, Maria Silvia Giamberini, Marta Magnani, Pietro Mosca, Antonello Provenzale, and Brunella Raco, 2019 The Nivolet Critical Zone Observatory: exploring relationships between carbon fluxes and geology; Geophysical Research Abstracts, Vol. 21, EGU2019-7913 - EGU General Assembly 2019
Antonello Provenzale, Ilaria Baneschi, Stefano Ferraris, Mariasilvia Giamberini, Massimo Guidi, Pietro Mosca, Elisa Palazzi, Maddalena Pennisi, and Brunella Raco, 2018 - Carbon fluxes in high-altitude prairies: results from the Critical Zone Observatory at Nivolet; Geophysical Research Abstracts Vol. 20, EGU2018-5531, EGU General Assembly 2018
Mariasilvia Giamberini, Antonello Provenzale, Simona Imperio, Ilaria Baneschi, Ramona Viterbi MONITORING MOUNTAIN GRASSLAND TO SUSTAIN WILD HERBIVORES, 2018, in NEREUS/ ESA/EC "The Ever Growing use of Copernicus across Europe's Regions", pages 134-135.
Baneschi I., Giamberini M.S., Viterbi R., Cerrato C., Imperio S., Ferraris S., Provenzale A. Changes in Alpine grassland of Grand Paradiso National Park (Italy): first results from CO2 fluxes monitoring programme, in Proceedings of the 6th Symposium for Research in Protected Areas - Conference Volume, 2- 3 November 2017, Faculty of Natural Sciences, University of Salzburg, Austria DOI: 10.1553/np_symposium2017s1
Ilaria Baneschi, Stefano Ferraris, Silvia Giamberini, Simona Imperio, Pietro Mosca, Antonello Provenzale, Brunella Raco, Ramona Viterbi The Earth Critical Zone and Ecosystem Observatory at Nivolet, Gran Paradiso National Park, Italy , ILTER 2017 annual meeting & LTER France meeting Nantes, France, Oct 2017
Ramona Viterbi, Ilaria Baneschi, Cristiana Cerrato, Stefano Ferraris, Silvia Giamberini, Francesca Giordani, Simona Imperio, Antonello Provenzale Set-up of a long-term study on the changes in Alpine grasslands owing to climate and grazing pressure modifications, First ILTER Open Science Meeting, Skukuza, South Africa, Oct 2016
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Last update: May, 2019