Areas of interest

The Vaud Alps region covers an area of approximately 700 km², with elevations ranging from 372 meters (Lake Geneva) to 3,210 meters (the summit of the Diablerets). Due to its location, this region is exposed to humid air masses from the West to the North, much like the entire northern side of the Alps, giving it a humid and cool climate compared to the more sheltered and sunnier inner Alps, such as the central Valais.

The average annual temperatures calculated for the period 1981-2010 range from 10 to 11°C along the shores of Lake Geneva and in the Rhône Valley in the Chablais, 3°C at 2,000 meters above sea level, and -3°C at 3,000 meters above sea level. The average monthly temperatures vary from 1.5°C in the coldest month (January) to 20°C in the warmest month (July) at low altitudes. At high altitudes, at 3,000 meters above sea level, temperatures range between -8.5°C and +4°C. Permafrost is present year-round on the highest peaks of the Vaud Alps. Valley bottoms can favor the accumulation of cold air, which influences average temperatures, especially in the colder season.

Precipitation also varies greatly depending on regional and local topography in the Vaud Alps. On average, 1,000 to 1,300 mm of precipitation fall annually in areas along the shores of Lake Geneva and in the Rhône Valley in the Chablais, whereas precipitation reaches around 2,400 mm per year on the peaks exposed at 3,000 meters above sea level. The precipitation regime is semi-continental, with higher rainfall typically occurring during the warm season (thunderstorms).

(Written in collaboration with Prof. Jean-Michel Fallot)

The Vaud Alps are part of a cantonal territory that contributes 8% to Switzerland's total production. Long benefiting from its appeal to both foreign and Swiss tourists, the economy of the Vaud Alps is largely based on activities directly or indirectly related to tourism. However, in recent years, challenges have been mounting, particularly due to the strength of the Swiss franc. Despite this, the Vaud Alps have fared better than other mountainous regions, thanks to the strong presence of business and conference tourism in the Lake Geneva region.

(Written in collaboration with Prof. Délia Nilles)

The Vaud Alps region covers an area of approximately 700 km², including the districts of Pays d'Enhaut, Aigle, and part of the Riviera. All vegetation zones (lowland, mountain, subalpine, alpine, and nival) are represented in the Vaud Alps, where the altitude gradient ranges from 372 meters (Lake Geneva shores) to 3,210 meters (the summit of the Diablerets).

A diverse and varied fauna inhabits the different vegetation zones. The distribution of species along the altitudinal gradient is directly linked to the habitats they can occupy. For instance, species living at high altitudes must possess a high physiological tolerance to cold, while species at lower elevations must be able to withstand competition with numerous other species. Factors affecting biodiversity distribution along environmental gradients include: 1) climate (e.g., temperature, which determines the amount of available energy), 2) spatial factors, such as the study area’s size, 3) the evolutionary history of species, and 4) biotic processes, such as competition or mutualism between species.

A large number of species have been observed in the Vaud Alps, including 1,974 species of insects, 34 species of arthropods, 166 species of mollusks, 15 species of amphibians, 14 species of reptiles, 64 species of mammals, and 26 species of fish. Some of the most iconic species include the black salamander in the Vallon de Nant, the golden eagle soaring over the highest peaks, the lynx, the pelias viper, and butterflies like the swallowtail and Apollo butterfly (source: Swiss Centre for Faunal Mapping).

In 2014, 153 bird species were observed in the Vaud Alps, including 142 breeding species. The most common species in coniferous forests include the dunnock, the coal tit, the crested tit, the goldcrest, the song thrush, the mistle thrush, the blackbird, and the rock bunting. Other species typical of mountainous regions, such as the capercaillie, the rock partridge, the three-toed woodpecker, and the yellow wagtail, are also present. High-altitude birds, including the tree pipit, the alpine accentor, the yellow-billed chough, and the alpine snowfinch, are also breeding species in this area. The Grangettes region (an ornithologically significant area), which is the most important wetland nesting site around Lake Geneva, hosts 68 breeding species, including the great crested grebe, the black kite, and the green woodpecker. This area is also an important nesting site for the European oriole, the nightingale, and the Eurasian reed warbler (source: Vogelwärte & Birdlife).

(Written in collaboration with Jean-Nicolas Pradervand)

Several major tectonic units are present in the Vaud Alps. A portion of the Riviera, around Vevey and Montreux, lies within the Subalpine Molasse. Further to the southwest, two large units share the rest of the Vaudois Alps: the nappes of the Prealps and the Helvetic nappes. These large units can be subdivided into several nappes. For the Prealps, notable nappes include: the nappes of the median plastic and rigid Prealps, the nappes of Niesen, Simme, Brèche, Gurnigel, the submedian zone, and part of the Ultrahelvetic nappes. The nappes of Morcles, Diablerets, Wildhorn (Mt-Gond and Sublage), as well as the Ultrahelvetic nappes, belong to the Helvetic unit. The region is also covered by Quaternary deposits, particularly in the Rhône Plain, where alluvial deposits can be especially thick.

(Written in collaboration with Prof. Jean-Luc Epard)

The geomorphology of the Vaud Alps is strongly influenced by the local geology and exhibits a rich diversity, linked to the variety of rock types and tectonic styles of the different nappes. In the Prealps, the slopes are often steep and vegetated. Where massive limestone is present, the rock faces are often well-developed. In these areas, cones and scree blankets are common. Numerous landslides affect the slopes of flyschs (e.g., La Frasse) or morainic slopes. In the alpine nappes (Helvetic), very high slopes alternate between rock faces and ledges.

The humidity of the climate in the Vaud Alps maintains a relatively low snowline, which explains the presence of several small glaciers on the northern slopes of the Dent de Morcles – Grand Muveran – Diablerets range. The retreat of these glaciers since the end of the Little Ice Age has revealed vast proglacial fields marked by well-preserved moraines (e.g., Martinets Glacier, Plan Névé). Past extensions of local glaciers are evidenced by large areas of Würm and Late Glacial morainic cover, as well as by numerous well-preserved late-glacial morainic ridges in the Prealpine massifs (high Veveyse, Hongrin, Col des Mosses, Etivaz valleys, La Forclaz).

Active periglacial forms such as rock glaciers are scarce due to the moderate altitudes and the relatively low elevation of the glaciers. However, the region contains several large fossil rock glaciers, such as those on the northwest flank of Mont d'Or or around Gummfluh.

Torrential activity is highly pronounced in areas with steep slopes and significant sediment loads. The Etivaz valleys, the southern slope of the Diablerets massif (Anzeindaz), and the Vallon de Nant are the sectors where this phenomenon is most active. Large alluvial fans can be observed in these areas. Elsewhere, fluvial accumulation forms are generally limited because the valleys are often deeply incised.

Karstic forms are particularly well-developed around the Tour de Famelon, with extensive lapiez fields. Unique karsts are also observed in the gypsum formations of the Cols Zone (Col de la Croix, Col du Pillon, Krinnenpass) and the Submedian Zone (La Lécherette).

(Written in collaboration with Dr. Christophe Lambiel and Prof. Philippe Schoeneich)

The hydrology of the Vaud Alps is determined by: (1) their location within Europe, which subjects the region to strong Atlantic influences on the climate; (2) their altitudinal gradient, meaning a significant proportion of winter precipitation can fall as snow; and (3) their position to the northwest of the main Swiss Alps range, leading to precipitation caused by strong orographic effects. Due to the substantial amount of winter precipitation falling as snow, the runoff in the watersheds is typically snowmelt-rainfall driven. The balance between the winter snowpack, summer melt, and direct runoff depends primarily on the altitudinal gradient of the watersheds. This gradient determines both the proportion of precipitation falling as snow and the duration for which the snow cover persists. This balance is not solely controlled by total winter precipitation but also by temperature, which affects the snowpack in each watershed. More generally, the hydrological response can be summarized as follows: (1) for low-altitude watersheds (< approx. 800m), runoff typically follows precipitation, although some may be temporarily stored as snow; (2) for mid-altitude watersheds (approx. 800m to 1,500m), there is usually winter snow accumulation, and snowmelt typically occurs in early spring; and (3) for high-altitude watersheds, significant snow accumulation can lead to a peak in snowmelt, making runoff occur later in the spring. Note that these altitudes are indicative and vary annually depending on the prevailing conditions in each watershed, and they also vary according to the watershed's aspect.

In summer, in some watersheds, the accumulated snow may be enough to maintain high minimal flow levels. Without this, river flow would be very low. However, it is still influenced by occasional convective storm events. High-altitude watersheds can contain very small glaciers (generally less than 5% of the watershed's surface), which also help maintain low flow during the summer. The contribution of groundwater is also important for maintaining minimal flow.

Human impact on hydrology is significant in most regions. Many watersheds are used for hydroelectric purposes, though this is more related to water transfers than to dams. Water is extracted and transferred to higher altitudes via tunnels, then returned either to its original river or to a river in a neighboring valley through small hydroelectric plants. Although the water storage capacity is relatively small, this type of abstraction can significantly alter the water volume in a canalized river and lead to sediment management issues.

(Written in collaboration with Prof. Stuart Lane)

The bedrock of the Vaud Alps region is primarily limestone, but schists, granites, and dolomites can also be found. Various types of soils are present, ranging from deep brown soils (brunisols) to leached brown soils (neoluvisols). Fine soils directly resting on the substrate (lithosols) are also observable, and these have a greater influence on the vegetation.

An alkaline pedogenesis is promoted by the presence of cations and carbonates. However, this can be followed by an acidic pedogenesis due to the leaching of carbonates. The accumulation of post-glacial loess in this region accelerates the transition to acidic pedogenesis.

(Written in collaboration with Dr. Carmen Cianfrani & Aline Buri)

As far back as available documents reveal, the Vaud Alps have long been a perfect example of what any rural and mountainous region exhibits in terms of sanitary and medical practices. Thus, from the Middle Ages, the presence of practitioners with varied skills is noted, ranging from herbalists and itinerant drug vendors, to "bone-setters" holding "secrets", surgeons, and midwives who acquired knowledge through practical apprenticeship, to some rare (at least before the 19th century) attestations of learned doctors with foreign university degrees, sometimes of great renown (such as, in the 18th century, Albert de Haller, who, though appointed inspector of the Bex saltworks, settled in the region for reasons unrelated to medicine). The medical and sanitary organization, like elsewhere, is governed by various regulations regarding epidemics, drug trade, and health control. Institutions for receiving and treating the sick also reflect what is observed elsewhere, with a few geographical specificities: long before the invention of the modern hospital in the 19th century, small hospice-type institutions along the plains of Chablais served pilgrims, treated the sick, and fed the poor. This proto-medical Alpine history also includes some practices on the margins of true medicine, such as the thermal baths known here and there, which—like the Lavey baths—would not be truly exploited medically until the 19th century.

If we are to speak of a "medical boom" in the Vaud Alps, it too is contemporary with the broader societal "medicalization" process observed elsewhere in Europe. This transformation includes the history of the medical profession's shift to a unified and professional body (through standardized training in medical faculties), the subordination of other healthcare providers (such as midwives and caregivers) to medical authority, and their marginalization or even legal prohibition (as seen with the large, vague category of "bone-setters"). This process also entails the construction of a medical system centered around infirmaries and modernized hospitals (in Aigle, Château-d'Oex, etc.), designed to meet the healthcare needs of the entire population, a process that began in the late 19th century and continues to this day.

One striking feature, however, significantly shaped the medical history of the Vaud Alps: the exploitation of specific geo-climatic factors. Indeed, through a broad societal and cultural movement, medical science began, in the mid-19th century, to recognize the therapeutic power of high-altitude air, and more generally, the Alpine environment as potent agents against various diseases, particularly tuberculosis. This vast movement turned the Vaudois Alps, and Leysin in particular, into the site of a true healthcare industry, orchestrated by influential promoters, entrepreneurs, and doctors, such as Auguste Rollier, known worldwide for his heliotherapy methods. Between the late 19th century and the 1960s, thousands of patients (at times several thousand at once) would ascend to the region to undergo long-term sanatorium treatments in large establishments or small clinics. These institutions, in addition to serving as places for treatment and scientific teaching, essentially became the economic backbone of the region.

After the golden age of sanatorium medicine, abruptly interrupted in the 1950s with the advent of new therapeutic methods, the transition to new uses was not without difficulty. Some institutions continued their medical vocation in other forms, while others were repurposed for tourism, education, or even demolished. Despite this shift, medicine, as a crucial driver of economic development and social transformation in the Vaud Alps, continues to shape the architecture of buildings, urban fabric, the very landscape, and beyond, influencing both the natural and cultural history of the region.

(Written in collaboration with Prof. Vincent Barras)

The Vaud Alps cover an area of approximately 700 km², encompassing the districts of Pays d'Enhaut, Aigle, and part of the Riviera. All vegetation zones (lowland, mountain, subalpine, alpine, and nival) are represented in the Vaud Alps, with an altitude gradient ranging from 372 meters (on the shores of Lake Geneva) to 3,210 meters (the summit of the Diablerets). The eight main environmental groups of Switzerland (Delarze & Gonseth 2008) are found in the Vaudois Alps: Free waters; shores and wetlands; glaciers, rocks, screes, and moraines; meadows and pastures; heathlands, edges, and megaphorbiaes; forests; pioneering vegetation in human-disturbed areas; plantations, fields, and crops.

At low altitudes, deciduous forests (mainly beech forests, with some oak forests in the warmest conditions) are found alongside anthropogenic landscapes (vineyards, meadows, fields, buildings, etc.). At mid-altitudes, the forests are naturally composed of beech and fir trees, although foresters favor spruce trees in these areas. Agriculture remains important, with many meadows and pastures. Higher up, spruce forests dominate, generally marking the upper boundary of the forest zone. Locally, larches and Swiss stone pines can be found. Rhododendron heaths are common in areas less grazed near the forest boundary, and alder bushes locally colonize abandoned pastures. Above this, the alpine zone is primarily occupied by alpine meadows, interspersed with large areas of scree and rocks.

(Written in collaboration with Dr. Pascal Vittoz)

The region of the Valais Alps, which corresponds to the canton of Valais, spans an area of 5,224.25 km², with altitudes ranging from 372 meters (Lake Geneva) to 4,634 meters (Pointe Dufour in the Monte Rosa massif). With the exception of the Lower Valais, which is exposed to humid airflows from the West and North, the rest of the canton is shielded from these airflows by the Bernese Alps, as well as from the Southwest to Southeast by the main ridge of the Valais Alps. As a result, the central and Upper Valais enjoy a much drier and sunnier climate compared to the rest of Switzerland, with only Ticino experiencing a similar level of sunshine.

Average annual temperatures measured from 1981 to 2010 are approximately 10 to 11°C in the Rhône plain, the Chablais, and central Valais, 2 to 3°C at 2,000 meters above sea level, and -3°C to -4°C at 3,000 meters. Monthly average temperatures range from 0 to 1°C during the coldest month (January) to 19 to 21°C during the warmest month (July) in the Rhône plain downstream from Leuk. At high altitudes of 3,000 meters, temperatures range between -10°C and +4°C. Snow and glaciers are present year-round on the highest peaks of the Valais Alps. The valley floors can foster cold air accumulations that influence average temperatures, especially during the cold season, notably in the Conches and Lötschental valleys.

Precipitation also varies significantly based on regional and local topography in the Valais Alps. On average, 550 mm of precipitation falls annually in the driest location in the Valais and Switzerland at Ackersand-Stalden, 600 to 800 mm in the Rhône valley between Martigny and Brig, as well as in the side valleys of the Valais Alps, and 1,000 to 1,200 mm in the Rhône valley in Lower Valais. Precipitation exceeds 2,000 mm annually on the peaks of the Chablais Pre-Alps and the main ridge of the Valais Alps (Grand St-Bernard) and even reaches 3,000 mm per year on the highest summits of the Bernese Alps.

The precipitation regime is semi-continental, with generally higher precipitation during the warmer season (thunderstorms) in the Chablais and the northern slopes of the Alps. However, this summer precipitation maximum is much less pronounced in Valais above St-Maurice, where a more or less marked winter precipitation maximum appears, similar to the Jura regions of Neuchâtel and Vaud. This indicates the influence of the oceanic climate, which diminishes as one moves eastward and into the Upper Valais. Near the main ridge of the Valais Alps and in the Simplon region, the regime changes significantly, with two precipitation maxima in spring and autumn, corresponding to a higher frequency of humid airflows from the Southwest to Southeast, originating from the Mediterranean. These create a blocking effect on the southern slopes of the Alps and the main ridge of the Valais Alps, resembling the characteristics of a north Mediterranean climate, similar to Northern Italy and Ticino.

Written in collaboration with Jean-Michel Fallot, Institute of geography and sustainability, FGSE

The canton of Valais is privileged to feature a wide variety of geological formations that are characteristic of the Alps. The Valais Alps are also distinguished by the diversity of the rocks that compose them. The region hosts both minimally metamorphosed sedimentary rocks at the forefront of the Alps and deeply transformed rocks formed during the creation of the Alps, as seen in areas like Simplon, Nufenen, and Zermatt. The Valais Alps have been the subject of geological studies since the 19th century and continue to be a topic of interest for both Swiss and international researchers.

The paleogeographic domains in the Valais Alps begin in the north, where molasse outcrops appear in a few locations near Bouveret. The left bank of the Rhône River between Monthey and Le Bouveret is made up of tectonic units from the Pre-Alps, which have been transported over long distances from the Penninic units on the southern side of the Rhône. The areas located on the left bank of the Rhône between Monthey and Martigny, as well as most of the land to the north of the Rhône between Martigny and Brig, belong to the Helvetic domain and form the "High Calcareous Alps." The massifs of the Aiguilles-Rouges, Mont-Blanc, and Aar represent the foundation (basement) of these units and are primarily composed of Paleozoic or older gneisses.

South of the Rhône, in the Val d'Entremont upstream of Orsières, and in the Saastal, outcrop Penninic units made up of Mesozoic sedimentary rocks, often associated with their Paleozoic gneissic basement. Higher up, in the upper sections of these valleys, now occupied by large reservoir lakes (Mauvoisin, Dix, Moiry), and in the Zermatt area, one can observe the rocks that once formed the ocean, the Tethys, whose closure was responsible for the formation of the Alps. The rocks that once constituted the continent to the south of this ocean now form the high peaks such as Mont Collon, Dent Blanche, Weisshorn, and the Matterhorn.

Valais is not only an ideal site to study the formation of the Alps, but it also offers the opportunity to observe the phenomena related to their erosion. It is worth noting that it was in the Val de Bagnes that crucial observations were made, which contributed to the glacial theory. This theory concluded that climate warming had led to the disappearance of glaciers that once filled the Alpine valleys in ancient times.

Written in collaboration with Jean-Luc Epard, Institute of Earth Sciences, FGSE

The geomorphology of the Valais Alps is closely linked to the glacial history of the region. During the various Pleistocene glaciations, glaciers shaped the landscape, carving out the valleys we recognize today, with the deep incision of the Rhône Valley and the numerous secondary valleys that connect to it in a more or less perpendicular manner.

The decompression caused by the retreat of the large valley glaciers has led to many slope instabilities, such as subsidence and landslides—most of which are inactive today—visible along the slopes of the Rhône Valley. In the side valleys, some of these landslides are still active. One such example is the Moosfluh landslide (Aletsch), which became active after the recent retreat of the Aletsch Glacier. Evidence of glacial erosion is also seen in the form of roches moutonnées, particularly present in crystalline regions like the Mont Blanc massif, the Aar massif, and the Dent Blanche nappe (Arolla-Zermatt region). While the till (ground moraine) covers much of the slopes, the moraine ridges from the early stages of the Late Glacial are relatively sparse, due to the steepness of the slopes and the remobilization of materials by slope instabilities (landslides, debris flows). Higher up in the valleys, the morainic structures from the Recent Dryas (Egesen stage) are often well preserved, as are the moraines from the Little Ice Age and the proglacial margins that continue to expand year after year as glaciers retreat more rapidly.

Due to the high altitudes, there is a significant number of rock glaciers in the region. However, the distribution of these forms is heavily influenced by the extent of valley glaciation. In the highest (e.g., Zermatt area) or wettest regions (right bank of the Rhône Valley), the altitude range favorable for rock glaciers is more limited due to the presence of glaciers. Therefore, rock glaciers are most abundant in valleys with moderate altitudes and relatively dry climates, such as in the Turtmantal or Val d'Entremont, for example. There are also large fossil rock glaciers that bear witness to the high rates of erosion that prevailed during the Late Glacial.

The cold conditions that prevail in the region are also conducive to the weathering of rock faces, a process that results in an abundance of rockfalls. These are particularly pronounced where high crystalline or limestone cliffs dominate. Shale rockfalls, on the other hand, are particularly favorable to solifluction, a phenomenon primarily active above 2,500 meters.

Both in the Rhône Valley and the side valleys, large alluvial cones testify to intense torrential activity, with the Illgraben system being the most emblematic. Many smaller systems are also present in all the side valleys, as seen in the torrent cones that rest on the alluvial deposits along the valleys.

Written in collaboration with Christophe Lambiel, Institute of Earth Surface Dynamics, FGSE

With the exception of the Doveria Valley, which flows toward Italy from the Simplon Pass, and the northern slopes of the Sanetsch (Sarine) and Gemmi passes, the entire canton of Valais is within the watershed of the Alpine Rhône, covering an area of 5,244 km², from the Rhône Glacier (ranging from 3,600 m to 2,208 m) to Lake Geneva (372 m). Currently, the Rhône originates from a lake formed at the front of the glacier, dammed by a glacial moraine. From the glacier to Lake Geneva, the Rhône covers 164 km, with an average gradient of 0.89%, though with significant variations depending on the sector. The average altitude of the watershed is 2,127 m.

There are several hydrometric stations in the Rhône basin. The oldest is located at the Porte-du-Scex, near the river’s mouth in Lake Geneva, where water levels have been monitored since 1863, and a limnigraph was installed in 1891. By 2015, 16 hydrometric stations were operational in the Alpine Rhône basin, seven on the Rhône and nine on its tributaries. Data is published by the Federal Office for the Environment in the Swiss Hydrological Yearbook.

The Rhône watershed has a high glaciation rate of 11% and includes some of the largest glaciers in the Alps, including the Grosser Aletschgletscher, Fieschergletscher, Gorner, and Corbassière glaciers. The natural hydrological regime of the Rhône is glacio-nival (upstream) to nivo-glacial (downstream); it is characterized by high flow rates in summer and low flow rates in winter. The average annual flow rate at the Porte-du-Scex is 180 m³/s (from 1905 to 2018). The average summer and winter flow rates are 263 m³/s and 97 m³/s, respectively. The commissioning of large hydroelectric facilities (Grande Dixence, Mauvoisin) in the late 1950s significantly altered the annual flow distribution. Before 1958, the average winter flow at the Porte-du-Scex was 72 m³/s, and after this date, it increased to 120 m³/s. This increase in winter flows is further intensified by current climate warming (fewer snow-related precipitation). The volume stored in the reservoir lakes is estimated at 1,195 million m³, which corresponds to 21% of the annual flow at the Porte-du-Scex. The highest daily flow recorded at the Porte-du-Scex was 1,363 m³/s on October 15, 2000.

The hydrological regime of the Rhône’s tributaries is primarily determined by the average altitude of the watershed. Solid storage (snow, ice) is essential and leads to a decrease in flows during winter, with a peak during the melt season. The type of regime is also influenced by the rate of glaciation. The large glaciated watersheds on the left bank (Vispa, Navisence, Borgne, Dranse de Bagnes) have a glacial-type regime, as do the Massa (Aletsch) and the Rhône upstream of Gletsch. In contrast, the valleys on the right bank, the Chablais region, and the smaller watersheds on the left bank (Printse, Réchy Valley) tend to have nival regimes. A few small watersheds (Illbach) have a torrential regime. Most rivers have been developed for hydroelectric production, which affects their regime, with many sections now having residual flows (especially in the side valleys) or a run-of-river regime (especially the Rhône).

Written in collaboration with Emmanuel Reynard, Institute of geography and sustainability, FGSE

Given the significant relief and their vast extent, the Valais Alps exhibit a great diversity of habitats (Delarze et al., 2015) and species. Indeed, the Valais Alps span from 372 m (Leman shores) to 4,631 m (Dufourspitze), covering all vegetation zones. Additionally, they intersect three biogeographical regions.

Western Internal Alps: This region includes the Rhône Valley and the side valleys. It is characterized by a subcontinental climate, with high summer temperatures, cold winters, and low precipitation. In the foothill zone, the oak thickets have largely been replaced by vineyards. In the driest areas (rocky zones), as well as in secondary positions, steppe meadows feature a floristic composition similar to that of Central European steppes (between Hungary and Mongolia). In the montane zone, xerophilous pine forests are natural, benefiting from dry conditions unsuitable for beech. Agriculture remains significant, with extensive meadows and pastures, and locally, medicinal plant cultivation. The pine forests are replaced in the subalpine zone by spruce forests, followed by larch and Swiss stone pine forests, which mark the forest boundary. However, these forests have often been replaced by pastures or heathland dominated by rhododendrons. Above this, the alpine zone is predominantly occupied by alpine meadows, interspersed with large areas of scree and rocks. The geological diversity of the Alps allows for the presence of all alpine habitats found in Switzerland (dry limestone meadows, fresh limestone meadows, ridge grasslands, acidic rocky meadows, acidic meadows of the upper alpine zone, snow basins, etc.). Finally, the nival zone is highly present, with vegetation limited to isolated plants in the most favorable situations, with a record at 4,507 m (Saxifraga oppositifolia on the Dom).

Northern Slopes of the Alps: This region includes the Chablais, between St-Gingolph and the Grand St-Bernard Pass, and is characterized by cooler temperatures and significant precipitation. In the foothill zone, forests are dominated by beech forests, which are interspersed with anthropized environments (meadows, fields), with lime and ash groves on the steep slopes. In the montane zone, beech and fir trees take over, but are often dominated by spruce, which is preferred by foresters. Agriculture remains locally significant with meadows and pastures. Spruce forests dominate the subalpine zone, forming the forest boundary, although they have often been replaced by pastures, alder groves, or rhododendron heathland. The alpine and nival zones are similar to those in the internal Alps, with a dominance of limestone rocks to the north of Martigny and siliceous rocks to the south.

Southern Slopes of the Alps: This region is quite small, covering only the southern slopes of the Simplon (Simplon-Dorf, Gondo). The temperatures are mild, but precipitation is very high throughout the year. The entire region is dominated by siliceous rocks. The montane zone is covered by acidophilic beech forests, which give way to spruce forests in the subalpine zone, with spruce accompanied by larch at the upper forest limit. Agriculture is now very marginal in this region. The alpine and nival zones are similar to those in the internal Alps, but only acidophilic environments are represented.

Written in collaboration with Pascal Vittoz, Institute of Earth Surface Dynamics, FGSE