From 7000 to 5300 cal. BP, the trajectory is along axis 1 of the NMDS (Figure 5). This trajectory is influenced by the dynamics of forest taxa such as mesothermophilous trees (Ulmus, Corylus, Tilia, and Quercus) and Abies. These taxa, combined with high abundances of monolete spores and saprophytic fungi (Cercophora), suggest a wet forested landscape. From 8200 cal. BP, the mesothermophilous trees are gradually replaced by Abies in Montane belt areas of the northern French Alps (David et al., 2002; David, 2010b; de Beaulieu et al., 1993). Indeed, the 8.2 ka event led to high humidity levels (Finsinger and Tinner, 2006; Magny et al., 2003; Tinner and Lotter, 2001, 2006), which facilitated the expansion of Abies and subsequently Fagus. In the north-western Alps, Fagus appeared between 7500 and 7000 cal. BP (David et al., 2002; Joannin et al., 2013; Rey et al., 2022, 2013; Schwörer et al., 2015; Thöle et al., 2016; Tinner et al., 1996; Wick and Möhl, 2006), which correlates closely with the beginning of the dynamic recorded in the Glières sequence. Since 6500 cal. BP on the Glières sequence, Abies forests exhibited a gradual decline allowing the expansion of Picea, especially from 5500 cal. BP. These changes coincides with the other records from the north-western Alps, although slight temporal discrepancies are also observed [e.g., 6000 cal. BP at Lake Annecy (David et al., 2002), and at Survilly (David, 2010b) around 5700 cal. BP]. These discrepancies may be due to local variations and/or to the variations in pollinic rainfalls recorded in each site and/or uncertainties in the age-depth models. This change in forest composition also coincides with what has been observed in the Alps, where Picea first colonized the eastern part at the beginning of the Holocene (Henne et al., 2011) and migrated progressively to the western part (van der Knaap et al., 2005) around 8500 cal. BP, arriving in the Swiss Alps between 7000 and 6000 cal. BP (Finsinger and Tinner, 2007; Rey et al., 2022, 2013; Schwörer et al., 2015; Thöle et al., 2016; Tinner et al., 1996). Although the appearance of Picea is relatively synchronous between all sites in the north-western Alps, the rapidity of the shift in abundance, when Picea becomes more abundant than Abies, varies depending on the sites. This delay may be explained by the difference in altitudes and by the spatial representativity of the pollen rain fall (local vs. regional) in the archives and by the fact that this major change in forest composition is thought to be the result of a combination and succession of anthropogenic and climatic disturbances (de Beaulieu et al., 1993; Wick and Möhl, 2006). In the western Swiss Alps, the increase in anthropogenic fires around 6000 cal. BP could explain the decline of Abies, which is very sensitive to such disturbances (Schwörer et al., 2015; Tinner et al., 1999; Tinner and Lotter, 2006). Conversely, these dynamics, followed by the colder and wetter conditions, that characterize the transition toward the Neoglacial period, probably favored the expansion of Picea (Pini et al., 2017; Rey et al., 2013; Schwörer et al., 2015; Wick and Tinner, 1997).

In the Glières sequence, concomitantly with the appearance of Picea around 5500 cal. BP, a significant increase in erosion is recorded affecting the silicate substratum but even more the carbonated ones, as evidenced by the detrital elements and Sr, respectively (Figure 6). Such an increase in erosion is reported at exactly the same time at lake Anterne located 35 km from the Glières Plateau. Although human impact cannot be totally excluded, this dynamic can be interpreted as a response to the transition toward the Neoglacial period characterized by colder and wetter climatic conditions, whether for Anterne (Giguet-Covex et al., 2011; Pansu et al., 2015) or the Glières Plateau. Indeed, first evidences of human activities are not recorded before 5300 cal. BP at Glières and even later at Anterne (possibly from ca. 4800 cal. BP; Giguet-Covex et al., 2014).

From the beginning of the important increase of Picea and decrease of Abies around 4700 cal. BP, the general vegetation composition trajectory seems mostly influenced by the development of the first agro-pastoral activities at a local scale (i.e., Podospora, Sporormiella, Poaceae, Plantago-type, local pastoral index) but also possibly at lower altitudes (i.e., Cerealia, regional agricultural index) (Figures 5, 6). However, the Abies/Picea succession recorded in the Glières reflects a regional dynamic triggered by several local anthropogenic activities in the area but not specifically those recorded on the Plateau des Glières. Indeed, no increase in fire signal is recorded in the Glières sequence, as is usually observed in other Alpine sites (Schwörer et al., 2015).

From 5300 to 4300 cal. BP, a first phase of landscape opening is recorded, leading to high levels of Poaceae and an increase in taxa richness (Figure 6). Although, this could be due to a change in edaphic conditions, which facilitated the development of a more hygrophilous vegetation (with abundant Cyperaceae and Poaceae taxa), the hypothesis of first human disturbances, locally on the Plateau, is favored. Many pieces of evidence provided by our record and synthesized through the agro-pastoral indexes lead us to this conclusion, which is otherwise supported by other palaeoenvironmental and archaeological research in the region. Pastoralism is suggested by the increase (flux and concentration) of spores of the strict coprophilous fungi, Sporormiella and Podospora (Figure 4), which only develop on the excrement of herbivores (Cugny et al., 2010; Etienne et al., 2013). While Sporormiella may originate from the entire catchment area, the high amount of Podospora spores, is interpreted as being due to the immediate presence of animals, probably directly on the peat bog (Etienne et al., 2013). Secondly, although the Plantago-type pollen does not occur in significant amounts during this period, it is present and its proportions increases more significantly at the end of this phase, that is, around the transition with the Bronze Age (Figure 3). This result may be interpreted as a delayed response of the vegetation to these first pastoral activities. Although, the presence of strict coprophilous fungi spores may not only be caused by domestic herbivores but also wild ones, the hypothesis of an anthropogenic impact on the vegetation trajectory is preferred based on the appearance of Cerealia pollen grains. Cereals were probably grown at lower altitudes, and attest to farming activities not very far from the Plateau des Glières. These results can also suggest a certain mobility of the mountain population in the area, with a subsistence based on both raising livestock and cultivating crops.

Such agricultural and pastoral activities are known in the Alps during the Late Neolithic period, from archaeological research and other palaeoenvironmental records. Several “sheepfold caves,” which were occupied in the Early and/or Late Neolithic, are known in the pre-Alps and Sub-Alpine massifs (Argant et al., 1991; Delhon et al., 2024; Ginestet et al., 1984; Martín and Tornero, 2024; Nicod, 2008; Nicod and Picavet, 2003; Remicourt, 2009). In particular, <8 km from the Glières Plateau around 620 m a.s.l. (Figure 7), the cave called “La Balme-de-Thuy” was occupied from the Mid-Neolithic period (Ginestet et al., 1984; Remicourt, 2009). At a more regional scale, archaeological excavations in Grotte de Diois (Vercors massif) have confirmed the presence of several herds between 6450 and 3950 cal. BP (Argant et al., 1991; Brochier, 1986; Carrier and Mouthon, 2010). In addition, some palynological studies in the Northern French Alps also mention the increase in pastoral and agricultural evidence, at the end of the Neolithic period. Indeed, further east, on the other side of the Swiss border, Plantago-type and Sporormiella are recorded in the Lake Champex at the same time and altitude (1467 m a.s.l) as in the Glières Plateau (Rey et al., 2022, Valais region). In addition, this phase coincides with the detection of sheep and cattle DNA between 5400 and 4400 cal. BP, in lake La Thuile (874 m) (Giguet-Covex et al., 2023) (Figure 7). The differences in the agro-pastoral intensity index observed between this lake (which is barely noticeable compared to the other periods at this site) and the Glières Plateau (Figure 7) may reflect more intense activity in the Glières than at Lake La Thuile or it may more probably be due to lake taphonomic differences in the indicators used for each site. At a more regional scale, some studies in the Swiss Alps mention the appearance of Cerealia, Plantago-type or spore of coprophilous fungi in the Late Neolithic (Dietre et al., 2017; Garcés Pastor et al., 2022; Gobet et al., 2003; Hafner and Schwörer, 2018; Pini et al., 2017; Schwörer et al., 2015; Stahli et al., 2006; Tinner et al., 2003). An increase in the frequency of anthropogenic fires due to the practice of slash-and-burn, has also been observed in the Swiss Alps and the Jura (Dietre et al., 2020, 2017; Doyen et al., 2016, 2013; Gobet et al., 2003; Schwörer et al., 2015). However, this practice does not seem to occur in the Glières Plateau as no significant increase in the fire signal has been observed (Figure 6). At a broader scale, agro-pastoral practices have also been documented further west in the Massif Central since the beginning of the Neolithic and seem to have intensified at the end of the Neolithic with the occurrence of Cerealia and the increase in spores of coprophilous fungi (Dendievel et al., 2019; Miras et al., 2018).

It now seems that evidence of these potential Neolithic activities can be found, with varying degrees of intensity, over a wide range of altitudinal belts in the northern French Alps. Could this recurrence confirm that agro-pastoral activities were practiced on a regional scale during the Late Neolithic, but with very local impacts on the landscape? During the Neolithic, small communities would have spread within Alpine territory, heterogeneously engaging in agro-pastoral activities in the area. This explains the variability of the anthropogenic signals recorded at sites in the northern French Alps, highlighting the development of these pioneering activities with very local impacts on vegetation.

The Bronze Age and Iron Age periods correspond to a phase with a high level of forest cover, which persisted for more than two millennia (Figures 3, 6).

Low intensity agro-pastoral activities were identified on the Glières Plateau and below until the Mid-Late Bronze age period. In contrast, numerous studies have identified increasing agro-pastoral practices during the Bronze Age in the Alps and Jura (Doyen et al., 2013; Dziomber et al., 2023; Garcés Pastor et al., 2022; Pini et al., 2017; Stahli et al., 2006; Tinner et al., 2003, 1996). However, these sites are situated at either lower or higher altitudes than the Glières Plateau. At that time, it seems that people preferred to invest in higher, more naturally open environments. A comparable situation to that at Glières, is observed at Lake Gers (1,450 m a.s.l) and Lake la Thuile (Bajard et al., 2020, 2015a,b; Giguet-Covex et al., 2023) (Figure 7).

From 3000 cal. BP (Late Bronze/Early Iron Age), concomitantly with the increase in the richness of herbaceous species, we observe an increase in intensity toward moderate activity intensities in the Glières (increase of Sporormiella, Sordaria, Plantago-type, agro-pastoral index) (Figure 6). In the Iron Age, around 2300 cal. BP the rise in the fire signal could also indicate the first important human-triggered land clearance, which mostly affected deciduous trees (especially Fagus), to develop the pastoral activities as suggested by the concomitant increase in local pastoral activity index.

Signals of moderately intensive human activity have been recorded during the Iron Age in Montane belt sites such as lakes La Thuile, Champex and Gers (Bajard et al., 2020, 2015b; Rey et al., 2022) (Figure 7). At high altitude (Anterne, Savine), the signal is much stronger (sometimes slightly later: end of the Iron Age) suggesting more intense pastoral activities (Giguet-Covex et al., 2014; Sabatier et al., 2017). The signal of pastoral activities recorded in the Glières seems weaker than in the Sub-Alpine or Alpine belts but greater than that recorded on sites in the Montane belts. This record may be interpreted as reflecting a specific local dynamic due to the topography of the Glières Plateau. Indeed, this flat topography may have favored early clearing of the forest, compared with other sites located in the same vegetation belt.

Although we have only one sample representing this period, it is characterized by the first appearance of Juglans and Castanea (around 2000 cal. BP). These two species, grown at lower altitudes, are indicative of the beginning of the footprint of the Roman civilization on the Alpine landscape. Doyen et al. (2016) also observed the development of these taxa in the peri-Alpine Lake Paladru. In addition, cultivated species originating at lower altitudes (Cerealia and Vitis) are detected (Figure 6). The fire signal is lower than during the Iron Age but is still at a high level. This may be due to the progressive abandonment of the slash-and-burn system for a system aimed at maintaining the open landscape (Doyen, 2013). Despite the occurrence of Plantago-type pollen grains, pastoralism does not appear to have been an important activity in the Glières Plateau.

For this period, numerous studies in the Alps have observed a development and diversification of agriculture (Tinner et al., 1996), that are characterized by varying degrees of intensity depending on the altitudinal belts (Giguet-Covex et al., 2023). Several Sub-Alpine/Alpine sites in the Swiss, Italian and French Alps recorded an increase of the agro-pastoral indicators during this period (Dziomber et al., 2023; Finsinger and Tinner, 2007; Pini, 2002; Thöle et al., 2016). In the Northern French Alps, pastoral activities are also mainly recorded in these high altitudinal belts, as for instance at lakes Anterne, Verney and Savine (Giguet-Covex et al., 2023; Sabatier et al., 2017). At lower altitudes, like the Plateau des Glières, the Swiss Lake Champex sequence also recorded an increase in agro-pastoral indicators (Rey et al., 2022). The authors suggest that the surrounding area may have been used as an “intermediate seasonal stopover to reach the grazing grounds at higher altitude.” This hypothesis is supported by the results of DNA analyses of numerous sites located at intermediate altitudes in the northern French Alps, such as lakes La Thuile (874 m) and Gers (1,450 m a.s.l) which also suggest moderate local pastoral activity (Giguet-Covex et al., 2023) (Figure 7). Pastoral activities also developed in peri-Alpine areas (Arnaud et al., 2016; Doyen et al., 2016, 2013). All this evidence reflects the expansion of livestock farming and pastoralism within the territory with the exploitation of all vegetation belts. However, there are some particularities, such as in the Bornes-Aravis massif as shown by the Glières sequence and the lake Bénit sequence. Indeed, no significant proportions of pastoral indicators are recorded for this period (Bajard et al., 2018) (Figure 7). These differences suggest greater local variability in human activities in the lower/intermediate belts, compared to the higher altitudes.

This period marks a transition between the dynamics observed previously and the Middle Ages. The trajectory is progressively negatively oriented along axis 2 of the NMDS (Figure 5), with the influence of cultivated taxa (Cerealia, Vitis, Castanea, Cannabis/Humulus). Indicators of local pastoral activity (local agro-pastoral index, Sporormiella, Plantago-type, Rumex-type) appear to increase during this transition (Figure 6), as they do in other sites at similar altitude, such as lakes La Thuile and Gers (Figure 7). In addition, at lower altitudes, agrarian activities increase, as evidenced by Cerealia, fruit trees and the regional index of activity (Figure 7). This last observation is more evident at Lake La Thuile probably because of its lower altitude, which would have favored the local development of these cultures, especially cereals as well as hemp and green beans as evidenced by pollen and sedaDNA analyses, respectively.

The temporal resolution of the Glières sequence does not provide a precise record of environmental dynamics and human activities during the medieval period. It is therefore difficult to cross-reference palaeoecological information with recent historical and/or archaeological works carried out on the plateau (Laissus, 2018, 2025). However, the trajectory illustrated by the NMDS analysis (Figure 5) highlights a profound change in the composition of the vegetation, with significant increases of cultivated taxa (Cannabis/Humulus, Castanea, Juglans, Cerealia, Secale, and Vitis) and pastoral indicators (Sporomiella, Sordariaceae, Plantago-type). The average of all these indicators represented by the agro-pastoral activity index (Figure 7) shows the most intense phase of agro-pastoral activities on the local scale and even on a more regional scale (with the cultivated taxa). The fire signal (concentrations and fluxes) also suggests an intensification of the human impact on the landscape in the High Middle Ages. In addition, this period is characterized by the greatest richness of pollinic taxa and constitutes the second major phase of landscape opening in this sequence (after the Late Neolithic).

In addition, Fagus declines sharply from the beginning of the medieval period and never recovers to its previous levels. This decline is probably the result of human activity. Fagus was an important component of ancient mountain forests and an excellent source of firewood (Rochel, 2017). It is therefore possible that its decline was directly linked to its use in charcoal pits to then produce the required resource in the glass and/or metallurgical industries from the end of Antiquity (Gouriveau, 2020). In geochemical measurements, titanium (Ti) and strontium (Sr) slightly increases throughout the medieval period, reflecting the first, but moderate, increase in erosion since the beginning of local human activities (Figure 6). This erosion phase affects more the silicated substratum than the carbonated ones compared to the early and probably natural erosion phase (Early to Late-Neolithic). This result may indicate that human activities and/or land clearance are more concentrated on the flat part of the Plateau des Glières made of flysch and marls, while the steep calcareous slopes on either side of the plateau are less exploited. This increase in erosion is in line with the results obtained by Rapuc et al. (2024) at a larger scale, that is, in the Arve and Rhône catchment areas upstream of Lake Bourget (including the Glières Plateau), who observed an increase in human triggered erosion during the Middle Ages. In addition, the oldest medieval archives dating to the 13th century revealed that the plateau was seasonally used for pastoralism until the 18th century (Laissus, 2018; Mélo, 2025).

Such an intensification of agro-pastoral practices is commonly recorded during the Middle Ages in various Alpine regions (Bajard, 2017; Garcés Pastor et al., 2022; Tinner et al., 1996; van der Knaap et al., 2012). From the High Middle Ages, the practices initiated in Antiquity became more established and diversified in the Jura (Doyen et al., 2013) and throughout the Alpine chain (Finsinger and Tinner, 2007, 2006; Giguet-Covex et al., 2023; Rey et al., 2013; Thöle et al., 2016; van Vugt et al., 2022). Whether at low altitude in peri-alpine lakes (Doyen et al., 2016; Messager et al., 2022) or at mid and high altitudes (Bajard et al., 2020, 2018; Giguet-Covex et al., 2014) in the north-western Alps, all the indicators of agro-pastoral activities increase and highlight a phase of agricultural intensification (Figure 7).

The single sample documenting the Late Middle Ages seems to show that these dynamics declined during this period. The fire signal, which has been analyzed at a higher resolution, shows a clear decrease in intensity at the end of the Middle Ages. These dynamics are consistent with other records in the same altitudinal belt, such as those from lakes Bénit and Gers, but run contrary to the other records from lower and upper vegetation belts in the North-Western Alps discussed in the previous sections (Doyen et al., 2016; Giguet-Covex et al., 2023; Rapuc et al., 2024) (Figure 7).