Dynamics of high-altitude environments as a life-support system to wild herbivores: carbon and moisture cycling, biodiversity and landscape modification

 

Lead Authors: CNR (S. Imperio, A. Provenzale, I. Baneschi), UIB (Tessa Bahiga Bargmann)
Contributors: CNR/PNGP (Bruno Bassano), University of Bergen ( Ole Reidar Vetaas), EURAC (Ruth Sonnenschein)
 

High-altitude mountain areas above the tree line are home to a rich biodiversity made up of species adapted to extreme environments, often rare and/or endemic, but also hosted for centuries human communities that have exploited and partly transformed the environment.

In the Gran Paradiso National Park (GPNP, www.pngp.it), large mountain ungulates, such as Alpine ibex (Capra ibex) and Alpine chamois (Rupicapra rupicapra), rely on high-elevation meadows 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, however, are semi-natural habitats, whose appearance partly derive from agro/pastoral activities. The progressive abandonment of management practices such as mowing and grazing from high-elevation mountain areas causes modifications to grassland that can affect its forage value for mountain wild 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 show 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). Moreover, fragmentation of semi-natural grassland 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), soil organic carbon fraction (Guidi et al. 2014) and the net ecosystem CO2 and CH4 exchange (Wohlfahrt et al. 2008, Imer et al., 2013).

Climate change is another risk factor for mountain grassland and its role of sustenance for large herbivores. An upward shift of alpine plant species, and consequent 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 (Dirnböck 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 reductions in snow cover alter 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 (ie 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 extreme impact events and climate variability.

In addition, the population dynamics of mountain ungulates is strictly related to seasonality: females give birth in early summer in order to take advantage of the entire growing season during lactation. Global warming and consequent shifting of plant phenology is expected to alter this equilibrium. 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. Possibly as a result of this earlier snowmelt and higher temperatures, the start of growth season for alpine grasslands (as for example revealed by NDVI changes) appeared to happen earlier and earlier during the last 30 years, in particular between 1990 and 2000. This change can be one of the reasons for the reduction of the Alpine ibex population, which drastically reduced from 1992 to 2008 owing to the lower kid survival during those years (Mignatti et al. 2012, Pettorelli et al. 2007). The rationale for this link is that the earlier start of the growth season for alpine grasslands leads to the presence of grass with lower nutritional value later in the season (July-August), when the Ibex mothers need to produce high-quality milk for the newborns, possibly leading to a lower-quality milk and weaker kids. This hypothesis, although plausible, is as yet unproven and it can be one of the crucial points where climate, grassland dynamics, and ungulate population dynamics meet with each other.

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 storyline is to quantify the health status of mountain grasslands using two case study areas in the Gran Paradiso National Park (Italy): Levionaz and Noaschetta. As an example, grasslands in Levionaz have been heavily exploited until 70s, through agro-pastoral activities that included the irrigation of meadows, after which only cattle were reared until 90s. At present, human abandonment in both sites lead to tree encroachment with species of low forage value (such as dwarf willows Salix sp., especially in Noaschetta). A preliminary survey in Levionaz grassland found that, despite the presence of diverse types of vegetation, the types of high pastoral value are very localized and not very extended (Martinasso 2014). In addition, important and concentrated meteoric events cause landslides and overflowing of streams that lead to rejuvenation of soils and impoverishment of grass diversity (especially in Levionaz).

These modifications can seriously affect both traditional landscape and herbivores demographic parameters (in particular weaning success and overwinter survival), in turn limiting the possibility of sustainable tourism, associated with the presence of populations of wild ungulates and pristine grassland conditions.

A parallel aim of this storyline is to quantify the fluxes of water and carbon in alpine grasslands, considering different types of environment and different geological settings, blending experimental measurements with numerical simulations. The study of fluxes will be conducted in the Levionaz area in future years, and will be compared with the flux and meteo-climatic data already available in other monitoring sites (Gimillan and areas outside GPNP). Isotopic methods will be adopted in order to characterize the soil structure and composition and the origin of C. Moreover, isotopic C analysis of CO2 and CH4 will help to reconstruct the carbon allocation in the soil and the redox processes which occur in the soil and at the soil-atmosphere interface.

The Hardangervidda National Park (HNP) is Norway’s largest national park, which spans three counties in western and southern central Norway. It was designated as a national park in 1981, and is one of the most popular areas for outdoor activities such as hiking, hunting, fishing and camping (www.hardangervidda.com). The area is also currently being used as a grazing area for sheep. As a result, HNP is not only an important area for conservation, but is also an area where management is met with challenges from the human impacts of tourism and of public and traditional use. The HNP is home to two species of ecological and biodiversity importance; the wild reindeer (Rangifer tarandus) and the black grouse (Tetrao tetrix). Their populations are known to respond to human impacts, and to small and large scale changes in vegetation cover. Vegetation and snow cover play vital roles in the provision of winter fodder for wild reindeer, and in the conservation of the remaining populations of black grouse.

Wild reindeer are often considered keystone species of the circumpolar region, because they influence ecosystem processes such as nutrient cycling and primary production (e.g. Olofsson et al. 2004). The reindeer population on the Hardangervidda plateau is the largest herd in Europe, and is therefore important for its ecological value, but also for its economical and recreational value for hunters and landowners (Bjerketvedt et al., 2014). Thus, a loss of this herd would have a negative impact not only for the ecosystem, but also for the people that depend on these animals for their livelihood. Wild reindeer in HNP have experienced frequent and extreme fluctuations in harvest numbers over the last six decades because data on herd size is uncertain (due to the sampling effort being unequal between years), there is a lack of data on recruitment and other life stage characteristics, and because there is a high variation in hunting success (Bjerketvedt et al., 2014). Thus, more reliable population data is sorely needed.

There are a number of factors that are known to affect reindeer populations. For example, human infrastructure has been shown to affect reindeer migration and movement corridors directly and indirectly, in both the short and the long term (Panzacchi et al., 2013). Population fluctuations of reindeer are also affected by climatic variation; high population growth rates have been linked to dry winters, and climate effects are probably more important at high population densities (Aanes et al., 2000). It has also been suggested that the suitability of winter pastures determines the effect that hunting has on population regulation, where reindeer with access to good winter conditions are regulated by hunting, and those with access to poor conditions are regulated by bottom-up processes (Tveraa et al., 2007). This indicates that hunting should be informed by the availability of good winter grounds for wild reindeer. As reindeer depend greatly on lichens as a food source in the winter, the estimation of lichen biomass is an important factor in the study of reindeer populations. Snow cover strongly affects lichen biomass and lichen heath development (Odland et al., 2014; Skogland, 1978), and lichen cover is known to be reduced by high precipitation and altitude (Odland et al., 2014). High long term grazing pressure, particularly in combination with summer and all-year-round grazing by reindeer (Kumpula et al., 2014) and sheep (Mysterud & Austrheim, 2008) is also known to reduce lichen biomass. However, moderately grazed ridges have been suggested to be richer in species than un-grazed areas (Vistnes & Nellemann, 2008), and (Odland et al., 2014) have shown that human control of reindeer migration can improve lichen biomass. Thus, an appropriate grazing regime and management by people has the potential to maintain reindeer grazing grounds. However, in order to inform the management of reindeer migration, more reliable information must be gathered on the distribution of lichen biomass which provides superior winter grazing areas for wild reindeer.

Another important species that is found in the HNP is the black grouse, which is considered threatened in Europe. Similarly to the wild reindeer, the black grouse is sensitive to human disturbance and landscape modification, and is rarely found near hiking trails, roads or footpaths (Immitzer et al., 2014; Patthey et al., 2012). Nevertheless, small scale habitat heterogeneity has been shown to promote grouse populations by providing a mosaic of patches of grass, shrubs and woody plants, which provide foraging ground as well as nesting and hiding places (Immitzer et al., 2014). Heterogeneity can be provided by various small scale disturbances, but grazing, while it is controversial in HNP, has previously been shown to be beneficial to both male and female black grouse individuals, provided that grazing pressure is not too high (Baines, 1996). This is likely to be linked to the reduction in insect numbers at high grazing pressures. Thus, the scale of grazing management should be relatively fine to ensure the conservation of a diversity of vegetation structures which are most beneficial for black grouse breeding success (Calladine et al., 2002), and mapping vegetation within HNP is therefore of high importance when managing for the conservation of black grouse.

Synthesizing census data from these focal species with vegetation cover over time will go a long way to informing effective conservation management. This project will be able to help solve two contentious issues within HNP; 1) the relative effect of hunting and climate change (i.e. increased snowfall and snow bed thickness) on reindeer populations, and 2) the effect of sheep grazing and traditional landscape use on black grouse populations. This ecological knowledge can be used to inform the optimal management of HNP for its ecosystem benefits, improve the management of its biodiversity, and avoid the worsening of social conflicts within the area.

 

References

Related to GPNP

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Bruelheide H., 2003. Translocation of a montane meadow to simulate the potential impact of climate change. Applied Vegetation Science 6: 23–34.

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Darmon G., Calenge C., Loison A., Jullien J.-M., Maillard D., Lopez J.-F., 2012. Spatial distribution and habitat selection in coexisting species of mountain ungulates. Ecography 35: 44–53.

Dirnböck T., Dullinger S., Grabherr G., 2003. A regional impact assessment of climate and land-use change on alpine vegetation. Journal of Biogeography 30(3): 401–417.

Fay P.A., Carlisle J.D., Knapp A.K., Blair J.M., Collins, S.L., 2003. Productivity responses to altered rainfall patterns in a C4-dominated grassland Productivity responses to altered rainfall patterns in a C4-dominated grassland. Oecologia 137(2): 245–51.

Grignolio S., Parrini F., Bassano B., Luccarini S., Apollonio M. 2003.Habitat selection in adult males of Alpine ibex, Capra ibex ibex. Folia Zool 52(2): 113–120.

Guidi C., Magid J., Rodeghiero M., Gianelle D., Vesterdal L., 2014. Effects of forest expansion on mountain grassland: changes within soil organic carbon fractions. Plant and Soil 385(1): 373–387.

Imer D., Merbold L., Eugster W., Buchmann N., 2013. Temporal and spatial variations of soil CO2, CH4 and N2O fluxes at three differently managed grasslands. Biogeosciences, 10: 5931-5945

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Mignatti A., Casagrandi R., Provenzale A., von Hardenberg A., Gatto M., 2012. Sex- and age-structured models for Alpine ibex Capra ibex ibex population dynamics Wildlife Biology 18(3): 318–332.

Parolo G., Abeli T., Gusmeroli F., Rossi G., 2011. Large-scale heterogeneous cattle grazing affects plant diversity and forage value of Alpine species-rich Nardus pastures. Grass and Forage Science 66(4) 541–550.

Pettorelli N., Pelletier F., von Hardenberg A., Festa-Bianchet M., 2007. Early onset of vegetation growth vs. rapid green-up: Impacts on juvenile mountain ungulates. Ecology 88(2): 381–390.

Pickering C.M., Rossi S., Barros A., 2011. Assessing the impacts of mountain biking and hiking on subalpine grassland in Australia using an experimental protocol. Journal of Environmental Management 92(12): 3049–3057.

Tasser E., Tappeiner U., 2002. Impact of land use changes on mountain vegetation. Applied Vegetation Science 5: 173–184.

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Wohlfahrt G., Anderson-Dunn M., Bahn M., Balzarolo M., Berninger F., et al. 2008. Biotic, abiotic, and management controls on the net ecosystem CO2 exchange of European mountain grassland ecosystems. Ecosystems 11: 1338–1351.

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Zeller V., Bahn M., Aichner M., Tappeiner U., 2000.Impact of land-use change on nitrogen mineralization in subalpine grasslands in the Southern Alps. Biology and Fertility of Soils 31: 441–448.

 

Related to HNP

Aanes, R., Sæther, B. E., & Øritsland, N. A. (2000). Fluctuations of an introduced population of Svalbard reindeer: the effects of density dependence and climatic variation. Ecography, 23(4), 437-443.

Baines, D. (1996). The implications of grazing and predator management on the habitats and breeding success of black grouse Tetrao tetrix. Journal of Applied Ecology, 54-62.

Bjerketvedt, D. K., Reimers, E., Parker, H., & Borgstrøm, R. (2014). The Hardangervidda wild reindeer herd: a problematic management history. Rangifer, 34(1), 57-72.

Calladine, J., Baines, D., & Warren, P. (2002). Effects of reduced grazing on population density and breeding success of black grouse in northern England. Journal of Applied Ecology, 39(5), 772-780.

Immitzer, M., Nopp-Mayr, U., & Zohmann, M. (2014). Effects of habitat quality and hiking trails on the occurrence of Black Grouse (Tetrao tetrix L.) at the northern fringe of alpine distribution in Austria. Journal of Ornithology, 155(1), 173-181.

Kumpula, J., Kurkilahti, M., Helle, T., & Colpaert, A. (2014). Both reindeer management and several other land use factors explain the reduction in ground lichens (Cladonia spp.) in pastures grazed by semi-domesticated reindeer in Finland. Regional environmental change, 14(2), 541-559.

Mysterud, A., & Austrheim, G. (2008). The effect of domestic sheep on forage plants of wild reindeer; a landscape scale experiment. European journal of wildlife research, 54(3), 461-468.

Odland, A., Sandvik, S. M., Bjerketvedt, D. K., & Myrvold, L. L. (2014). Estimation of lichen biomass with emphasis on reindeer winter pastures at Hardangervidda, S Norway. Rangifer, 34(1), 95-110.

Olofsson, J., Stark, S., & Oksanen, L. (2004). Reindeer influence on ecosystem processes in the tundra. Oikos, 105(2), 386-396.

Panzacchi, M., Van Moorter, B., Jordhøy, P., & Strand, O. (2013). Learning from the past to predict the future: using archaeological findings and GPS data to quantify reindeer sensitivity to anthropogenic disturbance in Norway. Landscape Ecology, 28(5), 847-859.

Patthey, P., Signorell, N., Rotelli, L., & Arlettaz, R. (2012). Vegetation structural and compositional heterogeneity as a key feature in Alpine black grouse microhabitat selection: conservation management implications. European journal of wildlife research, 58(1), 59-70.

Skogland, T. (1978). Characteristics of the snow cover and its relationship to wild mountain reindeer (Rangifer tarandus tarandus L.) feeding strategies. Arctic and Alpine Research, 569-579.

Tveraa, T., Fauchald, P., Gilles Yoccoz, N., Anker Ims, R., Aanes, R., & Arild Høgda, K. (2007). What regulate and limit reindeer populations in Norway? Oikos, 116(4), 706-715.

Vistnes, I. I., & Nellemann, C. (2008). Reindeer winter grazing in alpine tundra: impacts on ridge community composition in Norway. Arctic, Antarctic, and Alpine Research, 40(1), 215-224.

 

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