Other research projects in vegetation ecology

Plant ecology in the alpine belt

Climatic conditions in the alpine belt are strongly constraining plant growth. Hence, the large areas in the Alps above the treeline offer some interesting topics to plant ecology.

With the glaciers receding under climate change, large areas of moraine material are available for plant colonisation. Plant succession is studied since long, but mainly in relation to the time since glacier retreat. But time is not the only factor influencing colonisation because plants need water, which is not similarly available on glacier forefields. In a master project, 100 plots, liberated from the Otemma glacier in short time, were inventoried with precise description of the substrate and distance to water. The results clearly showed that colonisation is quicker (higher plant cover and higher species richness) on fine sediments and when groundwater is close to the surface.

In the Alps, the treeline was often studied and the limiting conditions for trees in the alpine belt are now quite well understood. Because of the soil warming under strong solar radiations, grasses and herbs can grow above the treeline. However, the conditions corresponding to the upper limit of grasslands, here called grassline, were less considered. On the basis of temperature monitoring in the GLORIA project, we assessed the climatic conditions at the grassline in Europe. We found that closed grasslands are present in sites where the mean growing season soil temperature is warmer than 4.9 °C, and the growing season length above 85 days. These values are quite similar to those observed at the treeline, in accordance with physiological thresholds for plant growth.

Publications

Bürli S., Theurillat J.-P., Winkler M., Lamprecht A., Pauli H., Rixen C., … & Vittoz P. (2021). A common soil temperature threshold for the upper limit of alpine grasslands in European mountains. Alpine Botany 131: 41-52.

Siegfried L., Vittoz P. & Lane S. (2023). Hydrological heterogeneity and the plant colonization of recently deglaciated terrain. Arctic Antarctic and Alpine Research 55: 2259677.

Response of subalpine-alpine vegetation to
recent climate changes and consequences on soil
organic matter dynamics

Many studies interested these last years to changes of high-alpine flora under climate change. But only few interested to the alpine grasslands. Moreover, as the same factors (climatic conditions, rock chemistry, topography) influence vegetation and soil formations process and dynamics, we can expect a parallel evolution of vegetation and soils.

This project aimed to assess the changes in plant composition of subalpine and alpine grasslands in the Swiss Alps by comparing former exhaustive plant inventories with recent ones. In parallel, the incorporation of organic matter and its stability in alpine soils in relation to topo-climatic conditions, rock chemistry and plant communities were studied along a gradient of snow cover, on calcareous and siliceous bedrock.

Snowbeds were the most affected by climate changes, with a shift in composition towards siliceous alpine grasslands, whereas the other grasslands were quite stable. Ecosystem controls on soil OM dynamics differed substantially according to the soil layer considered. The vegetation type influenced OM thermal stability in the litter layer, but not in the topsoil and subsoil. Indeed, the supply rate of fresh organic material and the physical and chemical characteristics of the pedogenic environment appeared to control OM stability in the topsoil and subsoil. Vegetation shifts, induced by recent climate changes, will likely have limited impact on soil OM dynamics in subalpine-alpine belts.

Publications

Liberati L., Messerli S., Matteodo M. & Vittoz P. (2019). Contrasting impacts of climate change on the vegetation of windy ridges and snowbeds in the Swiss Alps. Alpine Botany 129: 95-105.

Matteodo M., Ammann K., Verrecchia E. P. & Vittoz P. (2016). Snowbeds are more affected than other subalpine-alpine plant communities by climate change in the Swiss Alps. Ecology and Evolution 6: 6969-6982.

Matteodo M., Grand S., Sebag D., Rowley M. C., Vittoz P. & Verrecchia E. P. (2018). Decoupling of topsoil and subsoil controls on organic matter dynamics in the Swiss Alps. Geoderma 330: 41-51.

Climate change and land-use impact on wetlands in the Jura Mountains

Historical exhaustive plant inventories were used to assess the recent (1974-2012) evolution of plant composition in three wetland complexes. Five common plant communities were retained: Caricion davallianae, Caricion fuscae, Calthion, Molinion, Filipendulion.

We observed a general trend towards more nutrient-rich flora with less light at ground level. Species diversity declined, with typical species of each alliance replaced by species belonging to nitrophilous and mesophilous grasslands. The changes were particularly important in site, where grazing was banned 25 years ago. However, no trend towards drier conditions was detected, but communities showed a slight trend towards more a thermophilous flora.

The investigated wetlands in the Jura Mountains have suffered mainly from eutrophication due to land-use abandonment and N deposition. Areas with constant land use (grazing or mowing) were more stable. Hence, it is important to maintain or reintroduce the traditional practices in the wetlands: extensive mowing livestock grazing.

Publication

Rion V., Gallandat J.-D., Gobat J.-M. & Vittoz  P. (2018). Recent changes in the plant composition of wetlands in the Jura Mountains. Applied Vegetation Science 21: 121-131.

Invasive species along the Venoge

The Venoge, a river on the western Swiss Plateau, is subject to a strong invasion of neophytes. Seeds and/or fragments of Buddleia davidii, Reynoutria japonica, Impatiens glandulifera, … are dispersed by the river, with a potential competition of the neophytes on the native flora. Some parts of the river are considered as nicely preserved and are protected at national level.

Neophyte populations were inventoried in 2001 and 2012 along 18 km of the river and the populations were localised as precisely as possible. From these data, species distributions were modelled at 1 m resolution using ecological factors (topography, river sinuosity and curvature, tree cover, distance to infrastructure).

Publication

Descombes P., Petitpierre B., Morard E., Berthoud M., Guisan A. & Vittoz P. (2016). Monitoring and distribution modelling of invasive species along riverine habitats at very high resolution. Biological Invasions 18: 3665-3679.

Ecology and demography of Leontopodium alpinum

Although Leontopodium alpinum is an emblematic species of the Alps, only a few studies interested to its autoecology and demography. This study filled partly these gaps by exploring the autoecology of L. alpinum on the basis of species distribution models (SDMs), phytosociological relevés and a 3-year monitoring of populations in the Swiss Alps.

L. alpinum is found almost exclusively on limestone and ultramafic rocks. The SDMs shows that the species grows mainly in dry regions, above 2,000 m a.s.l., on steep slopes. According to the relevés, it is present in a wide range of subalpine-alpine open grasslands. As a light-demanding, it requires light at ground level, corresponding to open grasslands. For these reasons, dry conditions (summer-warm climate, draining soil, south-facing aspect and steep slope), high elevations and oligotrophic soils are important factors. Windy ridges are an alternative with the necessary light conditions.

The species forms small colonies (1-5, maximum 30 rosettes) with a few flowering stalks. After flowering, the apical meristem dies and one or two new axillary buds grow below the previous rosette, developing into short rhizomes. The new stalk produces sterile rosettes before flowering after 2–4 years. Levkovitch matrices on two stages (sterile and flowering rosettes) showed that rosette survival and clonal reproduction maintain long-lived populations. A change in the survival of sterile rosettes would had the strongest effect on population dynamics.

Publications

Ischer M., Dubuis A., Keller R. & Vittoz P. (2014). A better understanding of ecological conditions for Leontopodium alpinum Cassini in the Swiss Alps. Folia Geobotanica 49: 541-558.

Keller R. & Vittoz P. (2015). Clonal growth and demography of a hemicryptophyte alpine plant: Leontopodium alpinum Cassini. Alpine Botany 125: 31-40.

Stille J.S., Vittoz  P., Dickoré W.B., Haffer D. & Wissemann V. (2019). Experimentelle Untersuchungen zur Beeinflussung des Wachstums des Alpenedelweiß (Leontopodium alpinum) durch den pH-Wert des Bodens und durch Konkurrenz. Berichte der Bayerischen Botanischen Gesellschaft 89: 59-82.