Vivian Zufferey

Antoine Doncieux
email: antoine.doncieux@cefe.cnrs.fr

Olivier Yobrégat

Scott Prudham

Sophie Caillon

Delphine Renard

Agrobiodiversity dynamics in a French wine-growing region

Keywords: crop diversity, viticulture, cultural values, farmers local knowledge, cropping trajectory, Gaillac, ethnographic approach

Agrobiodiversity is a promising nature-based solution in the pursuit of sustainable agriculture. In wine-growing systems, commercial pressure and varietal regulations have narrowed agrobiodiversity in vineyards despite higher diversity being an important buffer against the effects of climate change. If drivers of grape diversity change are well-understood at national to global scales, little is known about the local, past or anticipated trajectories that drive agrobiodiversity dynamics depending on growers' cultural values, practices and choices. We combined quantitative agricultural census data and qualitative ethnographic approaches to characterise changes in the diversity of grape varieties from 1960 to 2020 at the communal and vineyard levels in a French wine-growing region, and to decipher the drivers of change. We highlight that vineyards have drastically changed in 60 years, with a decline in planted area and in farm number. We outline that despite a loss of varietal richness across both vineyard and communal scales, varietal richness remains high and evenness have increased across geographic scales in 2020. Ethnographic field observations emphasize that growers account for external drivers (e.g., market changes, regulation and policy, technology, environmental), but also cultural values when they choose which grape varieties to plant. Grape diversity was maintained despite market integration as an insurance to spread production risk, mitigate market volatility and address environmental uncertainties. Securing livelihoods in the midst of market changes has been a major concern for growers over the last six decades and remains so. Despite a pessimistic future vision of the vineyard shared by most growers, the Gaillac region has a cultural heritage that values diversity and that thereby supports adaptation to climate change. We expect that environmental factors may play a more important role in grape selection and planting sites in the future under the influence of climate change and pesticide reduction policies. In order to expand individual initiatives resulting in diversified grape selection, growers need to be better connected with stakeholders at a variety of institutional levels.

INTRODUCTION

Agricultural systems with higher crop diversity compared to monocultures support higher wild biodiversity, provide multiple ecosystem services [START_REF] Kremen | Ecosystem Services in Biologically Diversified versus Conventional Farming Systems: Benefits, Externalities, and Trade-Offs[END_REF][START_REF] Mcdaniel | Does agricultural crop diversity enhance soil microbial biomass and organic matter dynamics? A meta-analysis[END_REF] and are an important source of resilience to disturbances and the effects of climate change [START_REF] Kremen | Ecosystem Services in Biologically Diversified versus Conventional Farming Systems: Benefits, Externalities, and Trade-Offs[END_REF][START_REF] Renard | éditions de 2017 : contours des parcelles et îlots culturaux et leur groupe de cultures majoritaire[END_REF][START_REF] Snapp | Biodiversity can support a greener revolution in Africa[END_REF]. With the higher variability and unpredictability of climatic conditions, promoting crop diversity (hereafter agrobiodiversity) -from gene to species and from fields to landscapes -is a nature-based solution for reducing the risk of harvest and income losses while enhancing sustainability [START_REF] Altieri | Agroecology and the design of climate change-resilient farming systems[END_REF][START_REF] Lin | Resilience in Agriculture through Crop Diversification: Adaptive Management for Environmental Change[END_REF][START_REF] Renard | éditions de 2017 : contours des parcelles et îlots culturaux et leur groupe de cultures majoritaire[END_REF]. In this context, reports of agrobiodiversity erosion is a major concern [START_REF] Khoury | Crop genetic erosion: Understanding and responding to loss of crop diversity[END_REF]. Although an alarming loss of 75 % of global agrobiodiversity since the 1900s has been reported [START_REF] Fao | The second report on the state of the world's plant genetic resources for food and agriculture[END_REF], recent evaluations of trends in agrobiodiversity have shown contrasting results, mainly depending on the scale of analysis and choice of crop studied. Research has so far focused mostly on the main cereals (i.e., maize, rice, wheat, barley) and little is known about past changes in perennial crops, such as grapevines [START_REF] Khoury | Crop genetic erosion: Understanding and responding to loss of crop diversity[END_REF]. Because of their importance worldwide, changes in perennial cropping systems should also be assessed to improve the evaluation and understanding of the relationship between agrobiodiversity and agricultural resilience.

Grapevine is the world's third most valuable crop [START_REF] Alston | Grapes in the World Economy[END_REF]. During 8,000 years of domestication [START_REF] Grassi | Back to the Origins: Background and Perspectives of Grapevine Domestication[END_REF][START_REF] Maraš | Population genetic analysis in old Montenegrin vineyards reveals ancient ways currently active to generate diversity in Vitis vinifera[END_REF][START_REF] Myles | Genetic structure and domestication history of the grape[END_REF], diverse grapevine varieties (Vitis vinifera subsp. vinifera) have been selected and maintained by growers to fit local environmental conditions and to produce desired qualities in the crop [START_REF] This | Historical origins and genetic diversity of wine grapes[END_REF]. It is estimated that there are at present between 6,000 and 10,000 varieties of grapevine worldwide [START_REF] Alleweldt | Progress in grapevine breeding[END_REF], of which 1,100 are solely grown for wine production [START_REF] Wolkovich | From Pinot to Xinomavro in the world's future wine-growing regions[END_REF]. Each variety is a distinct genotype associated with a unique mixture of taste, colour, yield and climate-related functional traits, such as phenology and water use efficiency [START_REF] Schultz | Differences in hydraulic architecture account for near-isohydric and anisohydric behaviour of two field-grown Vitis vinifera L. cultivars during drought: Hydraulic conductance and stomatal behaviour[END_REF][START_REF] Wolkovich | Phenological diversity provides opportunities for climate change adaptation in winegrapes[END_REF]. In addition to the V. vinifera varieties, interspecific hybrids are widely grown for cold and disease resistance [START_REF] Bavaresco | Impact of grapevine breeding for disease resistance on the global wine industry[END_REF][START_REF] De La Fuente Lloreda | Use of hybrids in viticulture. A challenge for the OIV[END_REF][START_REF] Schneider | INRA-ResDur: The French grapevine breeding programme for durable resistance to downy and powdery mildew[END_REF]. Despite the wide range of varieties in existence and their varying traits, 16 varieties account for half the world's planted area (as of 2016, see [START_REF] Anderson | Which winegrape varieties are grown where? A global empirical picture[END_REF], and 12 or fewer varieties account for 70 -90 % of vineyard area in many countries [START_REF] Wolkovich | From Pinot to Xinomavro in the world's future wine-growing regions[END_REF]. Low diversity is seen as a possible source of vulnerability in the face of experienced and projected changes in climatic conditions, and in turn, a potential threat to viticulture (see [START_REF] Santos | A Review of the Potential Climate Change Impacts and Adaptation Options for European Viticulture[END_REF] for a review; [START_REF] Morales-Castilla | Diversity buffers winegrowing regions from climate change losses[END_REF].

In a review of 232 case studies, [START_REF] Khoury | Crop genetic erosion: Understanding and responding to loss of crop diversity[END_REF] show that global drivers of agrobiodiversity changes over time are numerous, interrelated and place-dependent; they include market demands and global integration, urbanisation, demographic shifts, industrialisation and modernisation of agriculture (particularly mechanisation), commercialisation and transformation of farm inputs (e.g., commercially bred varieties), regulation and policy (including appellation rules governing prescribed and proscribed types of grapes), and climate change. The globalisation of markets and the popularisation of particular varieties are considered to be primary drivers of the narrowing of the diversity of crops in general and of grape diversity in particular [START_REF] Anderson | Internationalization, premiumization and diversity of the world's winegrape varieties[END_REF]. Indeed, under the influence of the so-called New World model of winemaking and marketing, varietal wines such as Chardonnay, Sauvignon blanc, Pinot noir and Cabernet-Sauvignon have risen to the forefront since the 1980s, at the expense of varieties consumers may be less familiar with, or of blended wines whose varietal composition may be less apparent from labels and marketing (see e.g., [START_REF] Garcia-Parpet | Markets, prices and symbolic value: Grands crus and the challenges of global markets[END_REF]. Commercial pressures as well as national and regional varietal regulation through geographic indications also restrict growers to focusing on a handful of varieties (in general between 1-5 grape varieties in the French Appellation d'Origine Controlée system) that ostensibly match with their historical terroir [START_REF] Van Leeuwen | The concept of terroir in viticulture[END_REF].

If drivers of grape diversity decline are well-understood at national to global scales [START_REF] Wolkovich | From Pinot to Xinomavro in the world's future wine-growing regions[END_REF], little is known about local and wine-growing regional trajectories, past or anticipated. At these larger scales, past studies have suggested that multiple factors can promote agrobiodiversity locally, including ecological or economic factors (e.g., organoleptic features, productivity, maturation time) and cultural values, such as aesthetic values, the pleasure of collecting and discovering new varieties and the social significance of the cultivar as a marker of cultural heritage [START_REF] Brush | Dynamics of Andean potato agriculture[END_REF]Elias et al., 2000;[START_REF] Heckler | Piaroa Manioc Varietals: Hyperdiversity or Social Currency[END_REF]. Furthermore, the concept of terroir (particularly important in France) involves complex synergies between environmental (e.g., soil, climate, topography) and human factors, including cultural dimensions of wine-growing and winemaking practices that may be locally specific (e.g., vine training techniques) [START_REF] Van Leeuwen | The concept of terroir in viticulture[END_REF]. Terroir is a highly charged concept in which local identity and commercial imperatives have led to protectionist measures based on unique geographical indications [START_REF] Demossier | Burgundy: The global story of terroir[END_REF] and which are tied to specific viticultural and vinicultural practices, often based on particular and limited grape varieties [START_REF] Gade | Tradition, Territory, and Terroir in French Viniculture: Cassis, France, and Appellation Contrôlée[END_REF]. However, no wine-growing region is static. Environmental, economic, regulatory and cultural factors all drive changes in grape varieties and the way the wine is made. This means that terroir should not be understood as a static concept [START_REF] Anderson | Internationalisation of winegrape varieties and its implications for terroir-based cultural assets[END_REF], and that capturing the holistic character of agrobiodiversity dynamics at the local scale needs to incorporate farmer knowledge and the specific influences on farmer choices [START_REF] Berkes | Rediscovery of traditional ecological knowledge as adaptative management[END_REF].

In this study, we combine quantitative agricultural census data with qualitative ethnographic approaches in order to describe and analyse changes in the diversity of grape varieties planted at the vineyard to the communal scale between 1960 and 2020 in Gaillac, a French wine-growing region located in the Tarn department. Then, we deciphered the drivers of change and future expectation from the growers' point of view.

MATERIALS AND METHODS

Study area

The wine region of Gaillac is located in southwestern France in the Department of the Tarn (Figure 1). The total agricultural surface represents 51 % (i.e., ~ 300,000 ha) of the Tarn, of which 2.2 % (i.e., 6,541 ha) is occupied by grapevine (Data: Registre Parcellaire Graphique, 2017). Wine-growing takes place via 250 specialised farms, two vinicultural cooperatives and one wine merchant (Chambre d'Agriculture., 2020). In Gaillac, like in the South of France, [START_REF] Béringuier | La viticulture dans le Midi pyrénéen[END_REF][START_REF] Touzard | Deux décennies de transition viticole en Languedoc-Roussillon : De la production de masse à une viticulture plurielle[END_REF], cooperative cellars have played a key role in the wine-growing system since the early 20th century [START_REF] Rouvellac | Les spécificités et les difficultés du vignoble gaillacois, un siècle de reconstruction et de reconnaissance de la qualité[END_REF] and currently manage almost 50 % of the vineyard area.

The Gaillac region is home to seven Appellations d'Origine Contrôlées (AOCs) and two Indications Géographiques Protégées (IGPs) labels. Based on the concept of terroir and managed at the National level (by Institut National de l'Origine et de la Qualité, INAO) since 1935 [START_REF] Humbert | L'INAO, de ses origines à la fin des années 1960: Genèse et évolutions du système des vins d'AOC[END_REF], AOCs and IGPs are the top two tiers in the French wine quality hierarchy; they certify that the grapes from which the labeled wine is made originate from a particular location, though the geographic scope of the label can vary widely from a few fields to -particularly where IGPs are concerned -entire regions. The labels also signify and recognise compliance with aspects of wine-growing (e.g., permitted varieties, maximum yields), winemaking, marketing and land use. The white wine AOC dates from 1938 and 1970 for reds and rosés. The AOC limits cover 72 communes (i.e., the lowest level of administrative division in France) and a total agricultural area of 71,786 ha, of which 8.9 % were under vine in 2017. The wine production is estimated at 400,000 hl per year with ~ 35 % of volumes produced in AOC, 45 % in IGP and 20 % in VSIG (Vin sans Indication Géographique) (average 1996[START_REF] Spach | Enjeux économiques et politiques publiques de lutte contre la consommation nocive d'alcool en France[END_REF]IVSO, 2017).

Gaillac vineyards are a mixture of plains and hillsides (110-320 m). According to [START_REF] Riol | Le vignoble de Gaillac depuis ses origines jusqu'à nos jours et l'emploi des vins de Bordeaux[END_REF], four different terroirs have been identified from north to south: the plateau cordais, the premières côtes, the plaine du Tarn, the rive gauche terroirs (Figure 1). In addition to [START_REF] Riol | Le vignoble de Gaillac depuis ses origines jusqu'à nos jours et l'emploi des vins de Bordeaux[END_REF] mapping, Cunac terroir is located east of Albi and is not part of the white AOC. The climate is mainly dominated by oceanic influence, but subject to Mediterranean and continental ascendancies. Total yearly rainfall is 734 mm ± 125, and the mean annual temperature is 13.4 °C ± 0.59 (Data: Météo-France weather station of Albi, average 1990-2020). A strong zonal temperature gradient between plain and hillsides leads to ± 10 days difference in harvest date [START_REF] Delaunois | Description des differents terroirs du Gaillacois[END_REF].

Overall, there are 40 distinct grape varieties that can be used by growers to produce the AOC (14 varieties) or IGP (40 varieties) wines. Growers producing VSIG wines are not subject to any local regulatory constraints and can use the whole French national catalog of 324 wine grape varieties (FranceAgrimer, 2022). Some varieties, such as Len de l'el and Ondenc, are today only grown in Gaillac, and some, like Duras, were already being grown locally by the 15th century [START_REF] Tallavignes | Duras. In Traité général de viticulture -Ampélographie[END_REF]. The diversity of grape varieties and long-term winemaking practices in combination with terroirs results in the production of a large diversity of wines (including sparkling, dry, sweet, liquorous, orange, reds and rosés).

Data collection

Historical grapevine inventories in the Gaillac AOC

We assessed the spatial and temporal changes in the diversity of grapevine varieties in our study area by using two censuses from 1960 and 2020. The two datasets provided data for all current 72 communes within the Gaillac AOC. The dataset from 1960 was originally carried out by the Institut des Vins de Consommation Courante (ICVV) between December 1956 and March 1959 at the scale of the Tarn. We accessed this dataset from INRAE Vassal-Montpellier Grapevine Biological Resources Center (Marseillan, France). The dataset provides the number and size of farms and total area under each grape variety held by grower at the communal level. Data for the year 2020 was provided by the Casier Viticole Informatisé (CVI), which is an exhaustive national database, as declared individually by each grower. The CVI provided the area planted and the name of grape varieties at the grower level. The variables common to both data sets were the number of farms, the surface area of the farms, the number and the area of grape varieties within all communes.

We combined the two datasets using commune INSEE codes, the official geographic ID for listing communes in France. To ensure the comparability of the two databases, we checked whether the administrative boundaries of the communes did not change by georeferencing the 1960 cadastral map and compared it to the current communal division (OpenStreetMap) using QGIS (QGIS.org, 2022). We combined data for the four communes which merged and we used the 2020 commune boundaries as a reference for mapping.

Grapevine characteristics of Gaillac varieties

For each grapevine variety listed in our spatial-temporal dataset, we collected information about the use (e.g., as rootstock, table or wine grape production), berry colour, genetic identity (i.e., Vitis vinifera or hybrids) and phenology. We homogenised the variety names in the case of synonymy using the Vitis International Variety Catalogue (VICV). Berry colour was recorded for 188 grape varieties and genetic origin for the whole dataset. We defined international varieties according to the [START_REF] Robinson | The Oxford Companion to Wine[END_REF] classification and local varieties using the [START_REF] Plageoles | La saga des cépages gaillacois et tarnais en 2.000 ans d'histoire[END_REF] classification (see Supplementary Material for a detailed list). Data on variety phenology were collected from the Pl@ntgrape database, which includes the times of grape maturity (in weeks) as observed in the INRAE Domaine de Vassal Grape Collection. These times are provided using the Chasselas variety as a reference. On average, this variety reaches maturity (stage N on the Baggiolini scale) on 14th August (averaged over 50 years); i.e., on the 226th Day Of the Year (DOY). Syrah, for example, reaches maturity 2.5 weeks after Chasselas; therefore the time of maturity for this variety is expected on the 244th DOY. Finally, we classified the phenological times of the main grape varieties into three groups: early-season (≤ 237 DOY), mid-season (238-247 DOY) and late season (≥ 248 DOY). The phenological groups were built based on the local phenological classification used by the growers for harvest.

Local knowledge on grapevine varieties

We used an ethnographic approach to document the knowledge of local growers on grape diversity dynamics over time. Field study was carried out over eight months (February 2020 to November 2021), including participant observation and semi-structured interviews. We used participant observation based on relations of trust to improve our understanding of the wine-growing activities in the area. Capturing words is not the only means of collecting data in social and human sciences; in addition to organising informal talks, in this approach we not only observed people's practices and actions, but also got actively involved by, for example, helping winegrowers to harvest or prune their vines. We preferred to be outside when addressing topics related to sense of place and the future trajectories of the vineyard; it is difficult to address these topics and concepts via formal interviews carried out inside, where visual cues are less accessible and references to the landscape, terroir and specific practices are more abstract.

In order to investigate grape diversity from an emic perspective (the grower's point of view), it is necessary to identify the grape variety. Indeed, growers often refer to a folk classification to distinguish between two different varieties according to phenotypic variations (e.g., berry colour), while genotyping using simple sequence repeat markers can show very low genetic distances and identical variety [START_REF] Boursiquot | Essai de définition du cépage[END_REF]. Our study was based on the [START_REF] Boursiquot | Essai de définition du cépage[END_REF] definition of a variety: an array of clones resulting from the vegetative propagation of a single seedling. We thus transformed the varieties named by the growers into official names (e.g., Syrah for Sérine or Mauzac for Mauzac vert) using the VICV database.

The sampling strategy was developed to capture the heterogeneity of the grower populations. We interviewed 30 winegrowers (i.e., producers of both grapes and wines) and five vinegrowers (i.e., producers only of grapes which are sold to cooperative cellars or wine merchants). Both winegrowers and vinegrowers (hereafter all referred to as growers) were selected according to the number of grapevines varieties they grow, agricultural methods (conventional, organic and biodynamic), geographical localisation (across the four terroirs), seniority (number of years on the farm) and cultural inheritance (coming from a wine-growing family or not). Each grower cultivated from 3 to 18 (mean 10.4 ± 4.1) grape varieties. Our sample included 17 conventional and 18 organic and/or biodynamic farms, 17 growers came from the rive droite, eight from the rive gauche and ten from the plateau cordais. On average, the growers had been in charge of their farms for 23.5 ± 14 y/o. Lastly, 23 growers acquired their farms by inheritance and 12 are first generation growers.

The interviews were recorded (audio only) and they ran for two to four hours. The surveys consisted of mixed quantitative-qualitative questions and comprised three sections. The first section dealt with the history of the family and the farm, social information (e.g., date and place of birth, seniority in the farm) and professional background. The second section was a 20-minute discussion on issues related to grape vine diversity changes over time, drawing from maps of grape diversity changes between 1960 and 2020 that we had created using the data described in Section 2.1 (Supplementary Figures S1, S2 andS3). After the maps had been explained to the growers, they were asked to explain the background of wine-growing in 1960 and the past choice of grape varieties, and to give the main reasons for the changes in grape varieties over the last decades in Gaillac. Additional interviews were conducted with three retired winegrowers (mean age: 87 ± 2 y/o) to further explore the background of wine-growing during the second half of the 20th century with the help of maps. The final section of the interviews involved a series of open-ended questions regarding farmlevel grape diversity. We sought to establish i) grower interest in cultivating multiple varieties, ii) whether they planned to uproot or plant new varieties in the following 10 years, and iii) how they foresaw the future of the vineyard over the next 30 years.

Ethical considerations

We clearly explained the purpose of the project to all participating individuals at the beginning of each interview. All the interviews were voluntary and non-remunerated.

All the respondents remained anonymous and their answers were used strictly for the purpose of the study, and prior informed consent was obtained in writing. Our research project complies with the European General Data Protection Regulation (RGPD) on the protection of individual information under the reference 2-21088.

Data analyses

Quantitative analyses

All the statistical analyses was performed using R™ version 3.6.2 software (R Core Team, 2021). Statistical significance was set at α = 0.05.

Wine-growing system at the vineyard scale

In order to obtain all data at the communal level for the two dates, we aggregated individual data from CVI (2020) at that scale. Then, the data were summed for the 72 communes (i.e., vineyard scale) for 1960 and 2020 separately to determine the total area under vine, the area of each variety and the total number of farms. We estimated the average farm size in 1960 by counting the number of farms in each area category provided in the database ("< 0.25 ha", "0.25 ha-0.99 ha", "1 ha-2.99 ha", "3ha-6.99 ha", "7 ha-14.99 ha","15 ha-29.99 ha, "> 30 ha") and by averaging the total area under vine for each farm in 2020.

The proportion of each attribute of grape variety (i.e., berry colours, genetic identity, international or local grape variety and phenological groups) at the vineyard scale was calculated by dividing the summed area of each type of grape variety by the total area under vine for 1960 and 2020. We compared the area represented by each phenological group for the main grape varieties in 1960 and 2020 using Pearson's chi-square tests. To characterise the phenological variation across the main cultivated grape varieties at the vineyard scale, we first calculated the average and standard deviation of the potential ripening period for 1960 and 2020 respectively. Then, we compared the mean potential maturation period between 1960 and 2020 using a non-parametric Wilcoxon test (package stats version 3.6.2; R Core Team, 2021), because the data did not follow a normal distribution according to the Shapiro-Wilk test (W = 0.936, p < 0.05).

Spatio-temporal dynamics in grapevine diversity within the Gaillac AOC

We first quantified the diversity of grapevine variety in each of the 72 communes of our study region for 1960 and 2020 separately, using multiple indexes widely used in ecology: varietal richness, Shannon's H diversity index (calculated using vegan R package [START_REF] Oksanen | vegan: Community Ecology Package[END_REF]) and Pielou's J evenness index (Supplementary Equations ( 1) and ( 2)). The richness index is the number of grape varieties cultivated in a given commune. Shannon's H diversity index takes evenness and richness into account. The higher the value of H, the greater the number and evenness in the area planted in each grape variety in a given commune. A value of H = 0 would indicate a complete dominance of one grape variety in a commune. Pielou's J evenness index ranges from zero (indicating dominance) to one (indicating an equal abundance of all grape varieties). We compared the values of the three complementary diversity indexes between 1960 and 2020 with non-parametric Wilcoxon tests. For each commune, we then estimated how the composition of the set of grape varieties changed between 1960 and 2020 by computing a temporal beta-diversity index (TBI; [START_REF] Legendre | A temporal beta-diversity index to identify sites that have changed in exceptional ways in space-time surveys[END_REF] from the R package adespatial [START_REF] Dray | Perception and management of cassava (Manihot esculenta Crantz) diversity among Makushi Amerindians of Guyana (South America)[END_REF]. We calculated the TBI index using a Bray-Curtis dissimilarity matrix (distancebased matrix) on grapevine area data [START_REF] Legendre | Beta diversity as the variance of community data: Dissimilarity coefficients and partitioning[END_REF]. This index varies from zero (portfolios are exactly the same between the two dates) to one (portfolios have no shared varieties between the two dates).

Analyses of historical documents and growers' local knowledge

We first compiled the AOC varietal regulations framework from both 1960 to 2020. Historical documents were examined and relevant data were identified. We followed the guidelines provided by Olivier de Sardan (1995) to conduct and analyse individual interviews. First, the interviews were transcribed and analysed using the NVivo™ software (version release 1.5). Then, recurrent narratives from growers were identified, triangulated and described. The results are presented as both quotations and in summary narrative form and provide empirical evidence to support our arguments throughout the discussion. To maintain respondent anonymity, interview data are referenced by unique respondent numbers.

RESULTS AND DISCUSSION

Spatio-temporal dynamics of grape varietal diversity

Over the last 60 years, Gaillac vineyards have radically changed. In Gaillac, between 1960 and 2020, the winegrowing area decreased almost three-fold and the number of growers 22-fold; meanwhile, the average farm size increased six-fold (Table 2). We found that variety richness (Wilcoxon W = 4,524, p < 0.001) and evenness (Wilcoxon W = 185, p < 0.001) were both significantly different between 1960 and 2020, but we found a non-significant difference for the Shannon index (Wilcoxon W = 2,372, p = 0.87). A high TBIs index (0.93 ± 0.07) revealed that the portfolio of grape varieties was different between the two dates. In 1960, we inventoried 211 distinct grape varieties, including 74 Vitis vinifera cultivars (38 red varieties, 29 white and seven with undetermined colour) and 137 interspecific hybrids (77 red, 33 white, 5 varieties with another colour and 22 with undetermined colour). In the Gaillac region, hybrids occupied 22.5 % of the total wine-growing area at that time. Hybrids were originally developed in response to the phylloxera outbreak that devastated French vineyards at the end of the 19th century [START_REF] Gale | Dying on the Vine: How Phylloxera Transformed Wine[END_REF]. In 2020, the total number of varieties had dropped to 62 varieties, including 56 Vitis vinifera and six hybrids. Overall, 174 grape varieties were discarded and the loss of diversity affected more red (61.6 % of abandonment) than white (31.79 % of abandonment) varieties. Loss of varietal richness was mainly due to the abandonment of hybrids which represented 77.6 % of total grape varietal losses. Hybrids were barely represented in terms of area (0.2 %) in 2020. While two varieties (Mauzac blanc for white varieties and Jurançon noir for red varieties) dominated the landscape in 1960, the distribution of the cultivated areas between the different grape varieties was more even in 2020 (Figure 2).

The change in dominance was reflected by values of the Pielou index (Table 2).

Only 37 grape varieties were common to both dates, including two hybrid varieties (Villard blanc and Villard noir). Among these 37 varieties, the cultivated area has decreased for 20 varieties, on average by -79 % ± 29 %, and increased for 17 varieties, on average by 8,185 ± 28,410 % by a factor 0.2 to 118,000. Some varieties, such as the Valdiguié, have almost disappeared (area declined from 1,066 ha to 1.17 ha between 1960 and 2020) while other local varieties, like Mauzac blanc, have experienced a decline in area (from 6,006 ha to 594.7 ha), but still hold an important place in the vineyards.

Overall, the area planted with both international and local grape varieties has increased significantly at vineyard scale over the last sixty years and occupied a 32.6 % and 46.6 % of the total surface area respectively by 2020 (Table 2). The local variety Fer (named "Braucol" in Gaillac) experienced the most important increase in area, from 0.02 ha in 1960 to 975.4 ha in 2020 (Figure 2).

Between 1960 and 2020, growers introduced 25 new varieties, including four disease resistant varieties (Artaban, Floreal, Souvignier gris and Vidoc) selected by research institutes, and varieties from other winegrowing regions in France (Gamay from the Beaujolais region, Chardonnay from Burgundy region) and from Spain (Mourvèdre). Among these introduced varieties, Gamay currently occupies the largest share of area (11 %). Although non-significant (Wilcoxon W = 79.5; p = 0.95), changes in the portfolio of varieties induced a decrease in the range of the potential ripening period between the earliest and the latest grape varieties of two weeks between 1960 and 2020 (Table 2). We found a change in the proportion of grape varieties area within each phenological group over the 1960-2020 period (χ² = 6.22; p < 0.05). The proportion of early-season varieties (11 %) in the vineyard remained unchanged while growers cultivated more mid-season varieties (from 41.9 % to 59 %) and less late-season varieties (from 45.6 % to 29.8 %) in 2020 compared to 1960.

Over the 1960-2020 period, the communes located on the periphery (e.g., 62-Salvagnac, 61-Saint-Sulpice-La-Pointe, 36-Labessière-Candeil) of the vineyard were the most affected by vineyard area losses (loss from -70 to -99 %) and five communes (4-Arthès, 22-Combefa, 47-Mouzieys-Teulet, 58-Saint-Grégoire and 60-Saint-Marcel-Campes) experienced a total disappearance of wine-growing areas (Figure 3A 1,2 ). The spatial distribution of grape diversity changed between 1960 and 2020 (Figure 3B 1,2 , C 1,2 D 1,2 ). In 1960, the NW vineyards were characterised by a low number of grape varieties with low evenness, and the SE communes had between two and three times more varieties, with a more even share of the area according to H and J indices (Figure 3B 1 , C 1 D 1, ). The single commune of 53-Rabastens contained almost half (43 %) of total varietal richness in 1960 (i.e., 211 grape varieties).

In 2020, two communes (40-Lisle-sur-Tarn and 32-Gaillac) remained the hotspots of grape diversity (Figure 3 B 2 ), holding more than half of the total varietal richness at the vineyard scale (37 and 33 grapes varieties respectively).

Conversely, 25 communes grew less than ten distinct grape varieties. In addition, we observed a shift to red varieties in the communes where the Mauzac white variety was dominant -up to 76 % of the total planted areas for some communes like 10-Broze and 26-Donnazac in 1960.

Drivers of changes in grape varieties

Developing a good understanding of the drivers that influence grape diversity dynamics is essential for supporting sustainable agriculture [START_REF] Labeyrie | The role of crop diversity in climate change adaptation: Insights from local observations to inform decision making in agriculture[END_REF].

The investigation of archives and interviews revealed six classes of drivers that could explain the trajectories (i.e., loss, maintenance and gain) of wine-growing activity and grape diversity in Gaillac (Table 3). We documented anthropogenic (changes in market, policies, land use, agricultural technologies and demography) and environmental drivers which can synergistically interact across times and spatial scales. A good example of such interaction is for the Portugais bleu variety; we documented that i) its commercial outlets selling it as a vin médecin for improving the previous year's wines had disappeared, ii) the wine quality was not in phase with the AOC policy and new consumer habits, and iii) the latter was due to its high sensitivity to diseases (i.e., downy and powdery mildews, acid rot and Flavescence dorée). Each driver is described and discussed in a dedicated section.

Market change

One grower explained that "For the choice of grape varieties, it is the market that decides what growers plant […] because wine is not made for itself." (Grower 12). From local to global scales, changes in markets may be the most important driver of changes in crops in general [START_REF] Labeyrie | The role of crop diversity in climate change adaptation: Insights from local observations to inform decision making in agriculture[END_REF][START_REF] Martin | Regional and global shifts in crop diversity through the Anthropocene[END_REF], and grapevines are no exception [START_REF] Anderson | Internationalization, premiumization and diversity of the world's winegrape varieties[END_REF][START_REF] Moran | The Wine Appellation as Territory in France and California[END_REF]. In particular, the internationalisation and even globalisation of the wine trade has propelled important changes in the wine sector, including the privileging of particular varieties, some of which have become global brands. Change: A = addition; M = maintenance; L = loss. Source: the method used to identify the drivers and the trend. Numbers are referring to historical documents listed in Table 1.

As from the middle of the 20th century, wine consumption has undergone some broad changes. In many countries, such as France, Spain and Italy, per capita wine consumption in 2016 was only one-third of peak 20th century levels [START_REF] Anderson | Global wine markets, 1860 to 2016: A statistical compendium[END_REF]. In France, per capita consumption dropped after the 1960s, with a considerable decline in the demand for generic "table wines" (generally referred to as vin de France). Wine ceased to be the main drink, falling behind beer, soft drink or fruit juices, which are consumed by many young and urban people [START_REF] Barber | Capturing the Younger Wine Consumer[END_REF]. This phenomenon is explained by profound changes in consumer lifestyle (e.g., driving, continuous days of work as opposed to coming home for a midday meal), and a general increase in income [START_REF] Touzard | Deux décennies de transition viticole en Languedoc-Roussillon : De la production de masse à une viticulture plurielle[END_REF]. Daily wine is abandoned in favour of the occasional "pleasure wine" of "superior quality" of labelled appellation. These changes in consumption have created a gap between production and consumer demands. In Gaillac, the gap was closed through changes in grape varieties and cultivated areas.

In 1982, in our study region, the vin de France was the dominant form of produced wine, with a volume of 1,163,845 hl and representing 85 % of total production, while the production of AOC and IGP wines represented 5 % and 10 % respectively of total production. The AOC and IGP wines were mainly made by the cooperative cellars: 56 % and 67 % respectively of total production (average 1976-1980). Wine production was still valorised as bulk for 90 % of winegrowers in 1986, and was primarily marketed by wine merchants who were more interested in the quantity than in the quality of the wine. During the 1960-1990 period, local wine merchants remained practically the only commercial outlet for growers. Following other European growers, the race for increased productivity was recognised as a dead end and growers began to shift toward grape varieties adapted to new wine consumer habits (Figure 2). European regulations contributed to causing this shift (see Section 2.2). Grape varieties that were too productive, that could not reach the appropriate sugar level and that did not meet the market criteria were discarded by growers.

Growers selected grape varieties during visits to a specific vineyard; they looked at the land or the overall economic status of the farm (i.e., Merlot from Bordeaux or Gamay from Beaujolais). Grower 36 illustrated this choice: "At the end of the 1960s, I visited the Beaujolais region with a group of winegrowers. In a farm, in the yard, I saw two Mercedes [cars]. The winegrowers there looked richer, they were doing better. They had the Gamay, which seemed to make them money, then we brought the Gamay in our suitcases". However, to stand out from other vineyards and assert their local identity, growers have also chosen grape varieties with legacy values grown before the phylloxera crisis, such as Fer, Duras or Len de l'el [START_REF] Plageoles | La saga des cépages gaillacois et tarnais en 2.000 ans d'histoire[END_REF]. Following a wine blending tradition, popular varieties were used to improve wine quality based on local varieties. For instance, Duras and Syrah are usually blended, Duras providing a peppery flavor and Syrah bringing tannins, colour and aromas.

Market expectations also differ depending on type of wine (i.e., AOC, IGP and VSIG), which is an important factor for growers to consider when selecting grape varieties.

Although it is possible to produce IGP wines from AOC varieties, the latter is generally more restrictive (in multiple respects), and the growers reported the popularity and distinctiveness of grape varieties as being two characteristics that drive the market forces. As grower 10 explained: "There are not a thousand questions to ask, if you want to make IGP wine, you take the international grape varieties that are easy to sell as long as people know the name of the grape variety on the bottle. A Chardonnay, nowadays, is sold easily […] If you want to make AOC wine, you grow local grape varieties, there is a market with story-telling. In Gaillac, growers do both AOC and IGP wine." Consequently, international and local grape varieties coexist within the wine-growing system (Table 2). According to [START_REF] Wolkovich | From Pinot to Xinomavro in the world's future wine-growing regions[END_REF], the percentage of hectares in each region that is planted with international varieties varies across the globe, but is dominant in New World countries. For instance, international grape varieties represent more than 80 % of the planted hectares in China, Australia or New Zealand, because consumers clearly associate particular wine regions with specific and popular cultivars [START_REF] Verdonk | Importance, use and awareness of South Australian geographical indications: Geographical indications: importance and use[END_REF] (i.e. Syrah in Australia [START_REF] Carew | The Importance of Australian Corporate Brand and Grape Varietal Wines: Hedonic Pricing in the British Columbia Wine Market[END_REF] or Chardonnay in California [START_REF] Lima | Price and Quality in the California Wine Industry: An Empirical Investigation[END_REF]). By contrast, the majority of wine-growing systems in Old World countries are based on local grape varieties, for instance Touriga nacional in Portugal, Airén in Spain, Rhoditis in Greece or Sangiovese in Italy (Andersen and Nelgen, 2020). Today, Gaillac is putting emphasis on local grape varieties in order to produce highly distinctive wines that stand out in a standardised wine market.

Over the last few decades, Gaillac has adopted a counterflow strategy in contrast to other French winegrowing regions that have often built their identity over the centuries on a single grape variety [START_REF] Rouvellac | Les spécificités et les difficultés du vignoble gaillacois, un siècle de reconstruction et de reconnaissance de la qualité[END_REF]. In the Gaillac region, the multiplicity of wines is produced from a multiplicity of terroirs and grape varieties. But grape diversification is also perceived as a disadvantage for some growers: "The diversity of grape varieties dilutes the identity of the vineyard. The Cahors wine-growing region is associated with Malbec, the Bordeaux region with Merlot, but in Gaillac we do everything. This is an opportunity, but it is also pernicious. Consumers get lost with so much diversity, we are not identifiable on the market." (Grower 36). According to the interviews, the Gaillac region is trying to expand in too many directions at once and suffers from an overall lack of visibility, while varietal specialisation has successfully underpinned the renowned products of most wine regions (e.g., Burgundy, Picpoul de Pinet).

Policies to replace grape varieties

Coercive policies, first through national and then through European regulations, was applied to address overproduction in France and to respond to the competition at the lower end of the market from Spain and Italy [START_REF] Touzard | Deux décennies de transition viticole en Languedoc-Roussillon : De la production de masse à une viticulture plurielle[END_REF]. These policies strongly limited the individual freedom of growers to plant the grape varieties of their choice.

Over the 1953-2008 period, grape varieties were officially listed in three categories (recommended, authorised and tolerated) depending on how adequate the grape variety was for the terroir [START_REF] Galet | Cépages et vignobles de France (2e éd[END_REF] in each administrative subdivisions (e.g., départements in France). The specific varieties included in each category could be adjusted over time based on input from growers according to a prescribed process and some varieties were entirely discarded over time. Indeed, after restricting the use of tolerated varieties, which included hybrids, by cutting planting to 30 %, they were excluded altogether from the authorised list under penalty of punishment [START_REF] Montaigne | La réforme de l'Organisation commune du marché vin[END_REF], causing them to almost disappear in France in general [START_REF] Reynier | Manuel de viticulture: Guide technique du viticulteur[END_REF] and in Gaillac in particular (Table 2). Since 2008, a national catalogue has replaced the departmental classification and expanded the choice of varieties for growers of VSIG produce: from 60 varieties in the Tarn in 1982 to 324 in 2022.

European legislation has led to profound changes in wine-growing systems, in particular since 1976, through the implementation of regulatory measures such as the uprooting premium (designed to remove non-desirable varieties, as well as reduce the aggregate vineyard area) and planting rights regime (having permission to plant vines) [START_REF] Avallone | L'Union européenne et les dynamiques spatiales du vignoble français (1962-2016)[END_REF]. Gaillac growers grubbed up vines and earned financial compensation for approximately 15,000 ha of hybrids and high-yielding varieties over the 1972-1992 period. From 1982 onwards, the wine-growing area dedicated to appellation-labelled production was collectively restructured, containing up to 5,713 ha of awardwinning varieties between 1982 and 2016.

Within the framework of AOC regulation, the list of cultivable grape varieties has evolved over the last 60 years and has changed many times -up to nine times for red varieties (Supplementary Table S2). The AOC syndicate has also established a list of main and secondary grape varieties and guidelines for planted areas since the recognition of the red and rosé AOC in 1970. In 2022, for example, the proportion of main varieties (Fer, Duras, Syrah and Prunelard) grown in a farm must represent at least 70 % of total farm area classified in AOC, while secondary varieties (Cabernet franc, Cabernet-Sauvignon, Gamay, Merlot) cannot exceed 30 % of the area on farms included in the AOC area. Such regulations are common in the Old World, and are particularly associated with geographical indication and terroir-based regulation [START_REF] Meloni | Wine Regulations[END_REF][START_REF] Wolkovich | From Pinot to Xinomavro in the world's future wine-growing regions[END_REF], but they are, to our knowledge, not so common or quite rare in agrobiodiversity management in the rest of the world. Today, the spatial distribution of grape varieties in France (Supplementary Figure S4) is directly related to specific varietal regulations [START_REF] Wolkovich | From Pinot to Xinomavro in the world's future wine-growing regions[END_REF] [START_REF] Meloni | Wine Regulations[END_REF]; however, the possibility of increasing flexibility is currently being studied in France [START_REF] Aigrain | Quelles actions pour la filière vigne et vin face au changement climatique ? : Sélection de propositions issues d'une démarche participative et de la consultation d'instances professionnelles viticoles[END_REF].

Agricultural technologies and institutions

The choice of grape varieties made by growers has been influenced by the availability and affordability of new technologies, which have revolutionised agriculture over the past 60 years. As grower 34 noted: "Since the generalisation of phytosanitary products, the sensitivity of grape varieties to diseases is not an obstacle for grape choice". According to [START_REF] Morton | A Short History of Fungicides[END_REF], managing pest and fungal pathogen risks by applying chemical treatments are universal and ancient practices in wine-growing. In the 1960s, a new generation of fungicides was developed (e.g., benzimidazoles) characterised by low use rates, a broad spectrum and systemicity, which enabled extended spray intervals. These became very popular with growers. In turn, disease tolerant varieties, such as hybrids, lost their edge.

In the late 1970s, extensive research and experimentation have played a key role in the shift in grape varietal richness and evenness. Research aimed at breeding virus-free plants and identifying the best clones, variety-rootstock associations, pruning techniques and wine blending for a wide range of grape varieties, such as Duras, Syrah or Gamay.

Local agricultural advisors have been largely responsible for the dissemination of this knowledge by following up with growers, leading wine tastings and organising study trips and on-farm experiments of grape varieties. For instance, the Fer variety is irregularly fertile and requires a long-pruning system like Guyot. Because growers were used to short goblet pruning, new knowledge brought by agricultural advisors on pruning was decisive in the adoption of Fer in Gaillac. Today, the local section of Institut Français de la Vigne et du Vin pursues trials of varieties to select good candidates for resisting and adapting to climate change.

Similarly to research institutions, cooperative cellars have instigated a change in the grapevine varieties used by their members. Since the middle of the 1960s, they have conducted experiments for the selection of grape varieties and participated in the multiplication and distribution of grafts. In 1965, to incite growers to plant specific varieties, they introduced differential payment which depended on the grape variety; for example, growers of hybrids were paid less than those of Jurançon noir and Mauzac, who in turn were paid less than growers of Gamay, Syrah or Duras. Today, differential payments are still in place for one cooperative cellar, and they apply to Sauvignon, Cot, Colombard and Gamay, which are paid 10 % more per weight than other varieties.

Demographic change

In the early 1960s, the independence of Algeria entailed a massive influx of French European-descent migrants ("Pieds-noirs") to the Mediterranean area, including the Tarn department [START_REF] Toujas-Pinède | Les rapatriés d'Algérie dans la région Midi-Pyrénées[END_REF]. As shown by [START_REF] Brun | La réinstallation des agriculteurs pieds-noirs dans le Midi méditerranéen[END_REF], Pieds-noirs settlers caused profound changes in Mediterranean agricultural landscapes, like those in Corsica, the Var or Languedoc-Roussillon, by developing orchards, market gardens and vineyards. The Pieds-noirs farmers brought their knowledge and adopted agricultural innovations leading to profound changes to wine-growing systems in terms of grape varieties and the winemaking process. In Gaillac, most of them settled in the plateau cordais and rive droite. Historically, these were white-wine based terroirs, but the Pieds-noirs focused on the production of red grape varieties (e.g., Syrah and Merlot). Unlike most of the local growers, they i) did not rely on polyculture, ii) vinified the grape varieties separately, and iii) opted for indebtedness to build wine cellars and bought tractors. By producing more quality wines, some of Pieds-noirs farmers became a showcase for the vineyard and have been decisive in the recognition of the red appellation in 1970.

The sharp decline in the number of growers between 1960 and 2020 (Table 2) can be explained by the rural and agricultural exodus that occurred after Second World War.

In the 1960s, "everyone had vines. Whether it was the grocer or the baker. It was a way for them to save money." (Grower 38), but the shift from one grower generation to the next led to a withdrawal from and consolidation of wine-growing. For instance, many growers preferred more stable job opportunities for their children, such as jobs in administration. In 1987, 60 % of growers were more than 50 years old and more than one grower in two (55 %) declared no planned farm succession. In addition, wine cellars were under-equipped and required important financial investments in order to produce quality wine. Thus, the growers who did not engage in the restructuring uprooted their vineyards and several growers decided to shift their activity to cereal production, which is less strenuous and more profitable than winegrowing. The decrease in the number of farms has been accompanied by an expansion of farm area since the end of the 1980s, which has been accelerated by the European Union's Common Agricultural Policy (CAP) [START_REF] Gray | The Common Agricultural Policy and the Re-Invention of the Rural in the European Community[END_REF].

In addition, the proximity to Toulouse has boosted Gaillac demographically, accelerated by the construction of a regional motorway in 1992. Land competition between agriculture and urbanisation has significantly impacted the wine-growing areas, especially in the plaine du Tarn terroir, which follows the route of the motorway and remains a major concern for growers: "In Gaillac, bare land is more expensive than land turned into vine. We are not a vineyard valued enough, like Pessac-Léognan or the Champagne region, which manage to have real estate projects cancelled. For example, vine plots of the communes of Saint-Sulpice and Rabastens are now supermarkets, residences or industrial areas." (Grower 13). This local trend is part of a national phenomenon in France, where 2.5 million ha of agricultural land have been lost due to urbanisation during the 1960-2010 period [START_REF] Bertrand | Terres agricoles périurbaines : Une gouvernance foncière en construction[END_REF].

Incidence of environmental factors

Environmental factors (e.g., climatic hazards and disease outbreak) have played a minor role in the grape turnover (Figure 2 and Table 2) compared to the other drivers we have discussed. In Gaillac, the varietal regulation choice described in Section 2.2 was not fully based on the optimal climatic conditions for varieties at the vineyard scale. In the 1970s, late-ripening grape varieties, such as Fer or Syrah, had difficulty in attaining ripeness, especially on the hillsides, and were often rotten before harvest because of the rains at the end of September. Their inclusion in the AOC register have given rise to numerous debates. To produce wines, winemaking techniques (e.g., chaptalisation or specific yeasts) and canopy management practices (e.g., leaf removal) were promoted to compensate for lack of sugar and aromatic compounds.

However, when events become impactful and repetitive enough to challenge the sustainability of the farm, growers change the grape varieties to ensure minimal harvest. Among climatic hazards, the winter frost wave of 1956 and multiple late-spring frosts (1957, 1963, 1974, 1980, 1981, 1991, 1997 and 2017) Moreover, growing a rich portfolio increases the possibilities of wine blending by taking advantage of the organoleptic diversity of the grape varieties, which are useful for mitigating a bad year. For instance, in cold years, Merlot is used for increasing the sugar content of late-season Fer without the need for chaptalisation. Finally, a rich portfolio is also handy for dealing with wine market evolution by offering a wide range of products to consumers. As it is the case in many traditional farming societies, this diversity is used by growers as an insurance to overcome environmental and economic uncertainties [START_REF] Jarvis | A global perspective of the richness and evenness of traditional crop-variety diversity maintained by farming communities[END_REF][START_REF] Lin | Resilience in Agriculture through Crop Diversification: Adaptive Management for Environmental Change[END_REF] -a mechanism analogous to those underpinning resilience in natural ecosystems [START_REF] Loreau | Species Synchrony and Its Drivers: Neutral and Nonneutral Community Dynamics in Fluctuating Environments[END_REF][START_REF] Tilman | Productivity and sustainability influenced by biodiversity in grassland ecosystems[END_REF][START_REF] Yachi | Biodiversity and ecosystem productivity in a fluctuating environment: The insurance hypothesis[END_REF].

Cultural values to support varietal richness and evenness

The drivers described above cannot fully account for the changes in grape diversity we observed in Gaillac.

Ethnographic field work showed that cultural values, such as entertainment, experimentation with or habituation to varieties, contribute to explaining local agrobiodiversity dynamics.

During discussions, growers expressed their total commitment to growing several exigent varieties that require special attention in the field and in the winery cellar. As grower 2 related: "I would be very bored in Sancerre or Burgundy if I had to grow and vinify only one or two grape varieties".

Our ethnographic approach show that some growers are continually on the lookout for alternative varieties and expressed a strong feeling about the importance of experimentation with new grape varieties in the area: "The different grape varieties do not give the same thing depending on their region of origin. If we plant it, we can talk about it […] And we'll see if it will adapt to the soil, the climate, the environment and so on." (Grower 19). As shown by [START_REF] Rouvellac | Les spécificités et les difficultés du vignoble gaillacois, un siècle de reconstruction et de reconnaissance de la qualité[END_REF], growers in Gaillac are looking for in-depth knowledge about relationships between grape varieties and terroirs to produce quality wine. In practice, some growers use small plots of land and they observe and evaluate results over a certain number of years in order to determine whether their experiment meets their goals and expectations. If the trial is considered a success in terms of agronomic and wine qualities, the grower may decide to plant additional plots of these grape varieties. Knowledge gained from the experiment can then be passed on to other growers, impacting grape variety evenness at vineyard scale.

By contrast, knowledge gained through long-term history with specific grape varieties fosters trust and confidence in the variety and that it has the desired characteristics and qualities in relation to the terroirs. Grower habituation can lead to them maintaining the use of specific grape varieties and a reluctance to adopting new ones. For instance, the hybrids Jurançon noir and Portugais bleu were widely used by the growers and "had the trust of the growers, who were attached to them", as noted by grower 38. In the 1970s, growers were suspicious of novelty and only acted when they had been convinced by virtue of what they saw and by what paid off: "Growers were reluctant to plant the Fer variety, because they were used to other varieties, they did not believe in a legend that everyone was talking about and nobody had seen. Fer was unknown and had an irregular production reputation for people. They waited to see before acting." (Grower 37). As shown by [START_REF] Nicholas | Farm-scale adaptation and vulnerability to environmental stresses: Insights from winegrowing in Northern California[END_REF] in California, growers tends to rely on their own experience to guide their management decisions. Thus, long experience with a certain suite of varieties can lead to a reluctance by growers to change their grape portfolio, in the absence of new and direct experience with alternatives [START_REF] Kenny | The effects of climate variability and change on grape suitability in Europe[END_REF].

Further interviews to explore individual motivations may reveal more cultural values associated with grape varieties, such as patrimonial values [START_REF] Blonde | Vignes résistantes à l'oïdium et au mildiou: Promesses et controverses en Languedoc-Roussillon[END_REF]. Our interviews strongly suggested that cultural values, such as attachment-to-place/terroir and family/terroir legacy, are key factors that have been long underestimated and require further research. Such cultural values are also true for other crops; for taro (Colocasia esculenta (L.) Schot) in Vanuatu, [START_REF] Caillon | Les taros du Vanuatu: Que conserver et comment ?[END_REF] showed that motivations differed between the most common and the rarest varieties, which are associated with cultural and family heritage and memory values. Similar results can be expected for viticulture considering the longterm relationship that develops between grower and plant over the generations.

Expected trajectories of the Gaillac winegrowing system

According to the interviews, the respondents share a pessimistic vision of the future of the Gaillac winegrowing area: between a quarter and a half of the wine-growing surface area could disappear in the next 30 years if European institutions were to grant uprooting premiums. This finding is supported by a combination of factors currently impacting the wine-growing sector. More than one grower out of two (55 %) is over 55 years old and the majority of them no longer have a succession plan (IVSO, 2017). Despite the attractive price per hectare of land (10,500 €/ha), non-family facilities remain few and these have difficulty in accessing land with agricultural buildings, such as wine cellars, which are often not sold by retiring growers. Wine-growing -and more broadly agriculture [START_REF] Pawlak | Agricultural Potential of the EU Countries: How Far Are They from the USA?[END_REF] -suffers from a lack of attractiveness. This is exacerbated in a context of declining wine sales and public policies aimed at reducing alcohol consumption [START_REF] Spach | Enjeux économiques et politiques publiques de lutte contre la consommation nocive d'alcool en France[END_REF].

Facing doubts about the viability of wine-growing and the demographic future of the region, the vast majority of growers are caught up in the short term and have insufficient time to anticipate and plan adequately for the future. In Gaillac, the AOC appellations are not highly valued in comparison to other French AOCs, which means that considerable time and energy is put into wine selling, relegating other tasks and issues to the background. The growers emphasise that the collective momentum generated since the 1980s with the restructuring of the vineyard has stalled, and that they are currently moving forward individually. This group of growers plans to position AOC production on hillsides using local grape varieties and IGP production in the valleys using international grape varieties by combining irrigation, frost insurance and mechanical pruning for higher productivity. Emphasis will be placed on market diversification by producing both high-quality and generic wine for several outlets, including supermarket, restaurant, exportation and direct sales. However, this template is criticised by others growers, who i) may not have the assets to diversify their farms, and ii) as a result of their ecological values or ethics, refuse the use of irrigation and mechanical pruning.

Having to cope with climate change impacts on grape varieties, social demands and on-going environmental regulations about pesticide reduction is forcing both growers and institutions to further integrate environmental factors into their grape management.

As the local climate shifts, the yield and organoleptic properties of early-season varieties with low heat-tolerance, such as Gamay, could be severely impacted, leading to their decline and sometimes abandonment. Conversely, laterseason grape varieties, like Syrah or Muscadelle (which usually rots before harvest), are grown further up the hillside and the white varieties on the northern slopes. In addition, growers are beginning to rely on a new diversity of varieties and rootstocks that can cope with new temperature regimes through well-adapted functional traits, such as a later phenological events or better sugar-acidity balance (e.g., Bouysselet, Jurancon noir or Cinsaut) and drought-resistant rootstocks (R110 and Ru 140 on limestone soils) for new plantings. We expect that this will become more important as growers attach more and more importance to plant traits related to climate. As grower 22 noted: "I want to plant Chenin […] But when I think about the evolution of the climate, I wonder if it is wise to plant Chenin in Gaillac, because it appreciates cool temperatures and it is sensitive to latespring frost.

[…] Ten years ago, I would have done it without thinking about it". Moreover, growers are actually turning to or considering research-supported disease-resistant (downy and powdery mildews) grape varieties, such as Floreal or Artaban, while other growers are experimenting with old American hybrids like Noah or Othello. However, a majority of growers are still skeptical about these varieties, as they do not have enough knowledge about their susceptibility to trunk diseases, organoleptic potential and marketing opportunities.

Market demands, climate change and the need to reduce the use of synthetic chemicals in vineyards all call for increased flexibility and creativity in the selection of varieties. First, the new CAP reform (2023-2027) will allow growers to use disease-resistant varieties for AOC wine production. In addition, the INAO approved in 2018 the framework of the Variétés d'Intérêt à Fin d'Adaptation (VIFA) to experiment on new varieties; i.e., up to 5 % of the cultivated areas of a farm and up to 10 % of the mixtures over a period of 5 years (renewable once). How this translates into specific prescriptions within appellations, however, can vary depending on the influence of individual and institutional actors, including appellation syndicates, as well as the specifics of the growing conditions. Some appellations have already undertaken this testing device by reintroducing local, foreign or hybrid varieties. For instance, the Bordeaux region is experimenting with the Castets, Touriga Nacional and Alvarinho among the six approved VIFAs; and the Champagne region recently confirmed the application for approval of the hybrid variety that is resistant to downy and powdery mildew, known as Voltis, for the production of Champagne AOC. In the southwestern region and in Gaillac, VIFA measures are still under consideration and research institutes are listening to the needs of management bodies.

CONCLUSIONS

Our results highlight that despite the decrease in farm numbers and area, Gaillac vineyards are still diverse. Due to many grape varieties being available and terroir being heterogeneous, a large number of variations in wine-growing and winemaking systems are possible. Wine-growing is often perceived as a fixed system, but it has never stopped adapting. Different drivers, such as market integration and transformation, policy changes, demographic pressures, institutions and regulations, the development of new technologies and practices, have strongly contributed to grape diversity change over time and space at local scale. Whether seeking a niche market or a standardised market, the dynamics of grape varietal choice have been largely driven by market needs, and the choice is applied according to regulatory frameworks. Many case studies point out that farmers appear very sensitive to economic opportunities [START_REF] Labeyrie | The role of crop diversity in climate change adaptation: Insights from local observations to inform decision making in agriculture[END_REF]. [START_REF] Feintrenie | Are Local People Conservationists? Analysis of Transition Dynamics from Agroforests to Monoculture Plantations in Indonesia[END_REF], for example, observed in Indonesian agroforestry systems that economic dimension takes precedence over other values, such as cultural or sentimental attachment, and can quickly transform a diversified system into a monoculture. However, our study found that market integration does not necessarily mean lower crop diversity, as documented in previous studies [START_REF] Goldberg | Determinants of Smallholder Maintenance of Crop Diversity in Morocco's High Atlas Mountains[END_REF][START_REF] Vadez | Brief Communication: Does Integration to the Market Threaten Agricultural Diversity? Panel and Cross-Sectional Data From a Horticultural-Foraging Society in the Bolivian Amazon[END_REF].

Growers organise their grape portfolios to safeguard livelihoods in the future by ensuring new marketing opportunities. Thanks to cultural heritage and a strong attachment-to-place, the Gaillac region has one of the most diverse variety portfolios in France. Since diversification has been shown to be an important factor in mitigating the effects of climate change in vineyards [START_REF] Morales-Castilla | Diversity buffers winegrowing regions from climate change losses[END_REF] and in agriculture more generally [START_REF] Altieri | Agroecology and the design of climate change-resilient farming systems[END_REF], the results suggest that Gaillac vineyards may be relatively wellconstituted for offsetting climate change impacts.

Driven by growing concerns about environmental constraints, the crop trends we identified suggest a future evolution of grape portfolios. Recent political measures (national catalogue, CAP and VIFA) are allowing the winegrowing sector to increase in diversity at the local scale. This flexibility in the selection of varieties could enhance and strengthen the resilience of wine-growing systems at local scale in a future of dramatic environmental stresses.

To adapt to an ever-changing future, it is pivotal to pave the way for dynamic grape diversity management involving collaborative relationships between growers, researchers, conservatories and institutions that control regulations.

FIGURE 1 .

 1 FIGURE 1. Location of the Gaillac wine-growing region. The AOC delimitation of Gaillac is represented by bright colour, communes (N = 72) are delineated by a thin black line. The purple patterns represent the French wine-growing areas on the map of France and vine plots in Gaillac on the detailed map for the year 2021. The delimitation of the terroirs is represented with very thick lines: a) Plaine du Tarn (silty-sandy soils), b) Rive droite (carved out of claylimestone hills), c) Plateau cordais (limestone plateau), d) Rive gauche (high stony and rolled pebbles), and e) Cunac (red clay soil with gravel) terroirs. Data vineyards: INAO (2021), CVI (2020) and IGN (2021).

FIGURE 2 .

 2 FIGURE 2. Grape varieties turnover between 1960 and 2020. Main grape varieties cultivated in 1960 (N = 14 varieties, covering 92 % of total planted area) on the left side and 2020 (N = 13 varieties, covering 96 % of total wine-growing area) on the right side. Black crosses indicate that the variety was not cultivated and numbers represent the percentage of cultivated area. Barplot colours represent the ripening period of each variety: purple (early-season; < 237 DOY); green (mid-season (238-247); yellow (late-season; > 248 DOY) and grey (NA; missing values). Only the main grape varieties are represented for the sake of clarity.

FIGURE 3 .

 3 FIGURE 3.Communal-level diachronic maps (1960Communal-level diachronic maps ( -2020) ) of the wine-growing system.With A) percentage of communal area dedicated to wine-growing, B) varietal richness, C) H Shannon diversity index and D) J Pielou's evenness index for the 72 communes of Gaillac. The exponent 1 designates the map for 1960 and 2 for the 2020 maps. Numbers in the map A1 refer to the commune's location. A map locating all the different communes is published in Supplementary FigureS3.

TABLE 1 .

 1 Description of the historical documents reviewed. Numbers correspond with Table3.

	Titles	Authors	Dates	N°L
	e vigneron gaillacois au contact des réalités et tourné vers l'avenir. Dossier vert, 1ère partie, vins blancs.	Bonnet, M.	1963	1
	Le vignoble du Gaillacois. Mémoire de DES de Géographie.	Jalabert, J.	1967	2
	Situation du vignoble en 1970	Department of Agriculture	1970	3
	Le vignoble de Gaillac. Recueil des actes du millénaire de Gaillac 972-1972.	Cavaillé, A.	1975	4
	Rapports d'études sur l'expérimentation de différents cépages et de clones dans le vignoble de Gaillac	ITV-SICAREX	1977	5
	Schéma de restructuration du vignoble Tarnais	G.I.E des vignerons Gaillacois	1982	6
	Diplôme National d'OEnologie : Suivis OEnologiques dans le Gaillacois	Berthezene-Garda, S. and Lurton, L.	1984	7
	Enquête sur les structures des exploitations viticoles du Tarn	Rasse, E and G.I.E des vignerons Gaillacois	1987	8
	Bilan de la restructuration du vignoble du Tarn (1982-2015)	IFV	2016	9
	Développement d'une stratégie marketing collective pour les vins du Tarn	IVSO	2017	10
	Cahier des charges de l'AOC Gaillac	Official Journal of the French Republic	1970-2019	11
	Compte-rendu des réunions de conseil d'administration et d'assemblée générale (AOC et IGP)	AOC and IGP syndicates	1966-2020	12

TABLE 2 .

 2 Characteristics of Gaillac at wine-growing and communal scales for 1960 and 2020.

	1960	2020

TABLE 3 .

 3 Documented drivers of change in grape diversity over 1960-2020 period.

	Headings	Drivers of change	Examples	Change	Sources
		Change in wine consumption	A model of occasional consumption with high quality wine replaced the traditional model of daily consumption	A, L	interview, 1, 3, 4, 6, 7, 8
	Market change	Globalization of market	Grape varieties commercial reputation	A, L	interview, 2, 7
		Demarcation from other growers	Grape varieties distinctiveness amid standardized market	A, L, M	interview
	Policies	Varietal regulations	Incentive measures to force growers to focus on specific grape varieties via geographical indication	A, L, M	interview, 7, 11, 12
		Urbanization	Reduction of the cultivation areas	L	interview
	Land use	Replacement by other crops	Withdrawal from wine-growing, shift to cereal production	L	interview, 2, 3, 4, 9
		Difficulty of mechanisation	Steep slope hillsides	L	interview
		Oenological technologies	Increase in wine quality via oenological analysis	M, A	interview
	Agricultural		Experimentation of clone, varieties-rootstocks association,
	technologies	Insitution and knowledge	organisation of journey in another wine-growing regions,	A, L, M	interview, 5,7,8
			dissemination of knowledge to growers via agriculturar advisors
		Pesticide use	The sensibility of the grape varieties to diseases is not an obstacle for grape variety selection	A, L	interview, 7
	Demographic	Decrease in the number of growers	No farm succession, withdrawal from wine-growing activities	L	interview, 2, 3, 4, 6, 7, 10
	change	Migration	Pieds-noirs immigration led to red varieties shift production and bring new winemaking practices	A	interview
		Terroir suitability	Introduction of exotic grape varieties that match with soil types and local climate	A	interview, 1
	Environnemental	Desease outbreak	Disapperance of sensitive varieties to Flavescence dorée (e.g. Portugais Bleu)	L, A	interview
	factors		Grape diversity is used by growers as
		Diversification	an insurance to overcome environmental	M, A	interview
			and economic uncertainties
		Climatic hazards	Repetitive late-frost spring events	L, A	interview,1, 2

  including as specified within the 363 AOPs and 74 IGPs which account for 93 % of total wine production(INAO, 2020).Complying with the varietal regulations of the AOC standard "[are] a freely chosen constraint", as grower 7 conceded, but are also considered by growers as a complicated and rigid framework. As[START_REF] Cavaillé | Le vignoble de Gaillac[END_REF] already pointed out, in Gaillac, the regulations are confusing for growers and the boundaries are blurred between what is mandatory and what is not, or what will soon become one or the other. Varietal regulations can also become a burden for growers who are forced to keep a particular variety which may not always be suited to their commercial outlets or to the local terroir in a changing climate. By controlling wine-growing, winemaking, marketing, land use and water management, geographical indications can be too rigid and thus render adaption to climate change more difficult

Antoine Doncieux et al.

ACKNOWLEDGEMENTS

The research for this article was supported by the French National Research Agency (ANR) as part of the Programme d'Investissements d'Avenir (reference 17-MPGA-0004). We are most grateful for the time that growers from Gaillac generously offered to answer our questions. We would like to thank T. Lacombe and C. Marchal who helped to obtain data from the INRAE Domaine de Vassal Grape Collection, X. Raffenne and C. Granado from La Maison des Vins de Gaillac who helped with historical documents research, and C. Monmarthe from the French customs services who facilitated the handling of the CVI dataset.


Alessandra Insana
email: alessandra.insana@polito.it

Marco Barla

Jean Sulem

Energy tunnel linings thermo-mechanical performance: comparison between field observations and numerical modelling

Energy linings are receiving great interest due to their potential to transform a tunnel into a smart energy system for enhancing thermal comfort of buildings and metro stations, as well as to absorb waste heat from the tunnel environment. Yet, besides their thermal performance, the impacts of equipping segments with a net of pipes are still challenging in the framework of energy tunnels structural design. Indeed, the thermal regime of the concrete members is altered due to heat carrier fluid circulation. Hence, the need to shed some light on the possible limit states attainment arises. In this paper, field monitoring of stresses and strains are presented for the first time in relation to a full scale monitored prototype of Enertun energy tunnel lining installed in Turin, Italy. Experimental data are compared to the results of a coupled thermo-mechanical numerical model, showing to be in good agreement. Criticalities from the ultimate limit state do not emerge, although a deeper analysis of serviceability limit states attainment should be performed.

Introduction

Heating and cooling in buildings and industry represents a major share of energy consumption. National strategies have been formulated in recent years to sharply cut the use of fossil fuels and to manage energy use by adopting more efficient technologies. Renewable energy-based systems have been increasingly promoted and put into practice for their ability to contribute to reduce carbon dioxide emissions, to diversify energy supply and to reduce dependence on oil and gas unreliable markets.

In the renewable energy sources framework, shallow geothermal energy represents one of the possible solutions that can be adopted to fulfil heating and cooling needs. In particular, both a geotechnical and an energy role can be played by structures in contact with the ground, such as piles, diaphragm walls, base slabs, anchors and tunnels, turning them into energy geostructures, by appropriately deploying plastic coils for heat exchange [START_REF] Laloui | Energy Geostructures: Innovation in Underground Engineering[END_REF][START_REF] Soga | Energy geostructures[END_REF]. The possibility of thermally activating tunnels has been recently explored in different hydrogeological contexts, especially under the thermal performance point of view [START_REF] Di Donna | The role of ground conditions and properties on the efficiency of energy tunnels[END_REF][START_REF] Baralis | Geothermal potential of the NE extension Warsaw metro tunnels[END_REF][START_REF] Barla | Feasibility study for the thermal activation of Turin Metro Line 2[END_REF][START_REF] Epting | Geothermal potential of tunnel infrastructures e development of tools at the city-scale of Basel[END_REF]. However, major concerns still exist on the consequences that the flow of a heat carrier fluid subject to progressive heating or progressive cooling depending on the operation mode could have on the concrete members structural performance. Very few studies in literature dealt with this peculiar aspect. Among them, [START_REF] Nicholson | The design of thermal tunnel energy segments for Crossrail[END_REF] discussed the use of thermal tunnels with precast segments and the impact on structural performance with reference to the Crossrail project in London, where the need to cool the tunnel and the ground is crucial due to the noticeable heat generated by trains. By building a three-dimensional Finite Element (FE) Thermo-Mechanical (TM) model, they found that: -under natural heating the average hoop stress through the segment thickness increases by about 7% in summer compared to the as-constructed case (about 0.28 MPa).

-when heating mode operation superimposes to natural summer temperatures the hoop stress increases by about 9% compared to the as-constructed case (about 0.36 MPa).

-in winter negligible differences from the as-constructed case can be highlighted, both under natural conditions and with thermal activation of the geothermal plant.

-hoop stresses remain compressive at the extrados and intrados.

-local tensile stresses arise next to pipes, though remaining below the design tensile stress limit.

The mechanical effects were also investigated by [START_REF] Barla | Energy tunnels: concept and design aspects[END_REF] who built a coupled bi-dimensional TM model and assessed the stress state in the lining due to a one-year thermal activation summer-winter cycle. The thermallyinduced stresses, i.e. the stresses variations with respect to the as-constructed condition caused by the heat transfer process, were identified as being in the order of less than 1 MPa, with further compressions experienced by the lining during summer and decrease in compression during winter. No information on induced tunnel deformation was given. However, it appears that the range of stress variation is in line with the one suggested by [START_REF] Nicholson | The design of thermal tunnel energy segments for Crossrail[END_REF] as well as [START_REF] Mimouni | Thermomechanical characterization of energy geostructures with emphasis on energy piles[END_REF] who investigated the effects related to anchors thermal activation on a bored tunnel lining. According to the latter a maximum increase of up to 1.5 MPa is reached during heat injection, while tunnel diameter variation is below 1 mm. and slightly varies when considering silt or clay. These thermo-mechanical consequences are reputed relatively significant by [START_REF] Mimouni | Thermomechanical characterization of energy geostructures with emphasis on energy piles[END_REF], although [START_REF] Barla | Energy tunnels: concept and design aspects[END_REF] concludes that generally the design will not undergo substantial variations.

To systematically shed more light on the abovementioned aspects, an experimental and numerical study will be described in the present paper. First, the experimental campaign carried out, involving a full-scale prototype of energy tunnel lining Enertun-type [START_REF] Barla | Conci energetici per il rivestimento delle gallerie[END_REF], will be synthetized. Further details on the experimental site setup are outlined in [START_REF] Barla | A novel realscale experimental prototype of energy tunnel[END_REF]. Then two illustrative tests, one in heating mode and the other one in cooling mode will be discussed by presenting monitoring data pertaining to the lining stress-strain state. To the authors' best knowledge, thermo-mechanical experimental data for an energy tunnel do not exist in literature and hence can add a valuable piece to the puzzle of the understanding of energy tunnels thermo-mechanical behaviour. A numerical study is finally introduced and the methodology to simulate the two experimental tests is described. Comparison between monitoring and numerical outputs is carried out, by highlighting the variation in internal forces within the lining.

Experimental campaign

A full-scale prototype of energy tunnel comprising two rings was installed in 2017 in the tunnel under construction of Turin Metro line 1 South Extension in Italy, at a distance of about 42 m from the entrance of a station [START_REF] Barla | A novel realscale experimental prototype of energy tunnel[END_REF].

Turin subsoil is made of fluvioglacial deposits and presents an unconfined aquifer. In particular, in the location of the experimental site, the geological and geotechnical investigations allowed to define a stratigraphic profile mainly constituted by a sand and gravel unit, from loose to weakly cemented, apart from a shallow backfill layer. A West-to-East groundwater flow entirely intercepts the tunnel, whose axis is located at a depth of 16.6 m, with a hydraulic gradient between 0.3 and 0.5%. The phreatic surface can be found at a depth of about 12.4 m.

Energy segments were precast in the prefabrication concrete plant and then mounted by the TBM itself on site. The Enertun configuration, including both ground and air circuit, was adopted and tested for the first time to assess its efficiency by performing a number of tests in heating and cooling mode in 2018 [START_REF] Insana | Experimental and numerical investigations on the energy performance of a thermo-active tunnel[END_REF]. The two rings were connected in parallel to form the primary circuit, whereas a heat pump connected the primary circuit to the secondary one, represented by a fan coil unit. A comprehensive monitoring system was embedded within the precast reinforced concrete segments to investigate their thermo-mechanical behaviour. Indeed, one of the two rings was equipped with strain gauges provided with an embedded thermistor and pressure cells, all differently oriented, while in the second ring three pairs of Fiber Bragg Grating sensors were located. In the following the measurements obtained by the vibrating wire-based strain gauges and pressure cells will be considered, while a bespoke comparison among these and fiber optics-based sensors will be performed elsewhere. Fig. 1 depicts an as-built 3D view of the two rings with the monitoring sensors and the ground circuit (in blue). The details A-F show the orientation of the different sensors, reported also in Table 1 for the sake of clarity.

Description of a heating and a cooling test

A 7.8-days heating test (about 48 W/m 2 of heat extracted from the ground) and a 3-days cooling test (about 60 W/m 2 of heat injected into the ground) among those performed are selected in the present work to show the comparison with the results of numerical modelling described in the following. Fig. 2 and Fig. 3 depict the monitoring data recorded for these two tests respectively. For example, for the heating test, fluid inlet and outlet temperatures (note that inlet and outlet refer to the rings) are shown, as well as the tunnel temperature measured by a probe fixed close to the rings' intrados (Fig. 2a). Also illustrated are the subsequent temperatures in the lining (Fig. 2b), thermally-induced strains (Fig. 2c) and thermally-induced stresses (Fig. 2d).

As well clarified in [START_REF] Mimouni | Full-scale in situ testing of energy piles[END_REF], a correction of the strain measurements was needed to take into account the effects of temperature on the deformation of the strain gauges steel wire. It is highlighted that positive strains indicate contraction, while positive stresses indicate an increase in compression.

It can be seen that during the heating test the heat carrier fluid circulation led to a variation of temperature in the lining of about 4-6°C and to a thermally-induced contractive hoop strain of about 50 με. All pressure cells indicate a decrease in compression between 0.2 and 0.5 MPa. Analogously, during the cooling test the opposite behaviour is shown. For an increase in temperature of 5-7°C expansive strains are shown, in the order of about 60 με, despite the stress behaviour is not mirrored. Indeed, higher variations in stresses arise and it appears that a decrease in compression by 2.5-4 MPa is induced.

Numerical modelling

To better understand the thermo-mechanical phenomena occurring during the hydraulic flow and heat transfer process, a 2D coupled thermo-mechanical, finitedifference numerical model was built. In the following the methodology adopted is described, together with the analysis details and the results obtained.

Methodology

First a 3D coupled thermo-hydraulic (TH), model was built, calibrated and validated [START_REF] Insana | Experimental and numerical investigations on the energy performance of a thermo-active tunnel[END_REF] using the Finite Element software Feflow [START_REF] Diersch | DHI Wasy Software -Feflow 6.1 -Finite Element Subsurface Flow & Transport Simulation System: Reference Manual[END_REF]. Then, the tests presented in this paper were simulated by imposing inlet temperature, tunnel temperature and fluid velocity equal to the measured ones (again see [START_REF] Insana | Experimental and numerical investigations on the energy performance of a thermo-active tunnel[END_REF] for further details). The resulting temperature field obtained in correspondence of the cross sections where gauges are located (Fig. 4) was exported to a GIS (Geographic Information System) software. Hence, temperatures could be evaluated at the nodes of the TH model mesh. However, this discretization grid was different from the TM model one (Fig. 5) and an intermediate interpolation step was performed with the aim to get a continuous temperature field. This step was followed by the extrapolation of raster temperature values to the nodes of the TM model according to the shape given by the imported TM grid (nodes coordinates x,y). This process was repeated for both tests and both sections where stress and strain gauges are placed, at mid-thickness and at a longitudinal distance of 15 cm from the adjacent non-energy ring respectively. The nodal temperatures were then imported in the TM model at the end of the mechanical-only simulation of the excavation process by means of a user-defined function written in the FISH language.

Modelling procedure and input parameters

The finite-difference (FD) grid built in FLAC [START_REF] Itasca | FLAC ver.7.0 user's manual[END_REF] shown in Fig. 5 and consisting of 32268 elements is 74.8 m high and 149.6 m wide. The boundaries are positioned at a distance such as to minimize constraints influence on the area of interest. Horizontal displacements are prevented laterally, while vertical displacements are blocked on the lower side. As mentioned, the tunnel axis is 16.6 m deep and the tunnel diameter is 7.48 m. The model emulates the hydrogeological conditions existing in situ, characterized by a 2 m-thick backfill layer, above a sand and gravel unit (so-called Geotechnical Unit 2 or GU2, according to [START_REF] Barla | Turin subsoil characterization by combining site investigations and numerical modelling[END_REF]). After reproducing the geostatic conditions, a drained, time-independent analysis was performed to simulate tunnel construction using the convergenceconfinement method [START_REF] Panet | Le calcul des tunnels par la méthode convergence-confinement[END_REF]. The mechanical properties adopted for the different materials involved are listed in Table 2 (these values are inferred both from [START_REF] Barla | Turin subsoil characterization by combining site investigations and numerical modelling[END_REF] and from the final design report). A simple elastic model was used for concrete lining and grout injection, while an elastic-perfectly plastic Mohr-Coulomb model for the backfill and GU2. The calculation stages are recalled hereafter: -Initialization of stresses with the groundwater table at a depth of 12.4 m and surface loads. -Excavation simulation by deleting the elements within the excavation boundary and applying a gradually decreasing internal pressure until 20%. -Activation of the fresh grout and lining elements, and further 10% stress release. -Change of grout properties to its hardened state and complete stress release. -Definition of thermal properties (Table 2, where heat capacity and thermal conductivity match those assigned in the TH model), assignment of initial temperatures and uncoupled thermo-mechanical simulation (nothing occurs in this stage, which is useful to define the starting thermal point). -Reset of displacements, assignment of temperatures corresponding to the end of the tests and uncoupled thermo-mechanical simulation to assess the variation in the stress-strain state. At the end of the excavation the radial stresses range between -0.08 and 0.08 MPa, whereas the hoop stresses between -0.4 and 1.4 MPa (the crown intrados results slightly in tension).

Numerical results

The thermally-induced radial and hoop stresses and the thermally-induced hoop strains at the end of the simulation of the heating and cooling tests are shown in Fig. 6 and Fig. 7 respectively. The sign convention is the same as the one for experimental results. As it can be seen, no relevant variation in radial stress occurs (<0.08 MPa) neither for heating (Fig. 7a) nor cooling (Fig. 7b), which is different from what was observed experimentally. This could be due to different thermal expansion coefficients of the grout and the concrete lining. Hoop stresses at mid-thickness are compatible in the numerical simulations and in the experiments and indicate a decrease in compression for the heating test (between -0.14 and -0.38 MPa in the numerical simulation and between -0.21 and -0.26 MPa in the experiment) and an increase in compression for the cooling test (between 0.4 and 0.58 MPa in the numerical simulation, but between 3.1 and 3.6 MPa in the experiment). The mismatch in cooling mode could be due to the simplified assumption of monolithic lining, that does not take into account the segmental nature of the energy ring. The direction and amount of strains variation is also consistent, as extension is obtained upon cooling and contraction upon heating both at the extrados and at the intrados, as in Fig. 2c and Fig. 3c.

Based on these results internal forces acting on the lining were calculated and compared to the as-constructed case (Fig. 8). The combinations of axial force and bending moment N-M corresponding to maximum axial force, maximum bending moment and minimum bending moment were computed and represented together with the strength envelope of the representative cross section of the lining. It was found that these forces are largely included in the envelope, thus showing the little influence of thermal activation on the ultimate limit state of the lining. Moreover, it can be observed that the order of magnitude of stresses and strains variations does not exceed the one due to natural temperature variations and presented in [START_REF] Barla | A novel realscale experimental prototype of energy tunnel[END_REF]. Hence, although thermally-induced effects are not negligible, they are not considered to threaten the structural integrity of the lining. Further verifications are needed to verify the lining with respect to the serviceability limit state of stress limitation and cracking control.

Conclusions

This study focussed on the thermo-mechanical behaviour of energy linings, which is still little studied and deserves a special attention to boost the uptake of energy tunnels around the world. The methods employed included (i) full-scale in situ testing and (ii) numerical modelling. The experimental activity presented the evidences of the thermally induced stress-strain performance of such structures. The TM numerical analyses aimed at providing a fundamental characterisation of the response of energy tunnels to thermal and mechanical loads. The results illustrated allowed concluding that thermal loads acting on tunnels in alluvial soils involve effects that can be neglected in performance-based design of the lining at ultimate limit state. Indeed, little variations in internal forces were detected in comparison to the as-constructed condition. However, the effects of thermal loads still need to be investigated at the serviceability limit state.

Fig. 1 .

 1 Fig.1. 3D view of the experimental prototype with detail of pipes ground circuit and monitoring system (S=strain gauge, P=pressure cell, t=hoop direction, r=radial direction, l=longitudinal direction, i=intrados, e=extrados, 1-6=segment numbering from inlet to outlet). In orange is the key segment.

Fig. 2 .Fig. 3 .

 23 Fig. 2. (a) Heating test with corresponding (b) lining temperature, (c) thermally-induced strains and (d) thermallyinduced stresses.

Fig. 4 .

 4 Fig. 4. Temperature field obtained from the 3D TH finite element model at the end of the (a) heating and (b) cooling tests within the cross section where pressure cells are located.

Fig. 5 .

 5 Fig. 5. Finite difference mesh of the thermo-mechanical numerical model with stratigraphy.

Fig. 6 .

 6 Fig. 6. Numerical results in terms of thermally induced (a) radial stresses and (b) hoop stresses across the lining thickness at the end of the heating test. In black are experimental results..

E3S

  Web of Conferences 205, 06008 (2020)

Fig. 7 .

 7 Fig. 7. Numerical results in terms of thermally induced (a) radial stresses and (b) hoop stresses across the lining thickness at the end of the cooling test. In black are experimental results.

Fig. 8 .

 8 Fig. 8. Computed axial force and bending moment along the tunnel lining at the end of construction, of the heating test and of the cooling test.

Table 1 .

 1 Orientation and location of the monitoring sensors deployed in ring 179 of the experimental site.

	Segment number	Vibrating-wire strain gauge	Pressure cell
	1	-	P t 1
	2	Sl2i, Sl2e	Pl2
	3	-	P t 3
	4	St4i, St4e	Pr4
	5	-	P t 5
	6	St6i, St6e	Pr6

Table 2 .

 2 Mechanical and thermal model properties.

	Property	Backfill	GU2	Grout	Lining
	γ [kN/m 3 ]	15.5	17	18.5	25
	Ey [MPa]	15	190-240	5-5000	35200
	υ [-]	0.35	0.3	0.25	0.2
	φ' [°]	36.5	38	-	-
	c' [kPa]	1	30	-	-
	σt [kPa]	1	15	-	-
	λ [W/(mK)]	2.26	2.26	0.655	1.12
	cp [J/(kgK)]	1209	1209	1184	876
	αth [1/K]	1•10 -5	1•10 -5	1•10 -5	1•10 -5

https://doi.org/10.1051/e3sconf/202020506008