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Since the middle of the 20th century, the landscape mosaics of the tropical regions have been undergoing socio-ecological changes that threaten the resilience of small-scale agriculture. In response to these changes, farmers in some regions have diversified their cropping systems by developing agroforests (associations of trees with other non-perennial species and/or animals, in space and time). To do so, they use plant diversity, whether cultivated or not, and develop different agrobiodiversity management practices that are adapted to socioeconomic and biophysical contexts. My research aims to analyze these agroforestry dynamics implemented by farmers with a case study in the landscapes of the North-East coast of Madagascar, which show a recent evolution from subsistence agriculture based on slash-and-burn cultivation to complex and multistage agroforestry. The three sections of my thesis study different components of the local agrobiodiversity management (farmers’ practices and knowledge, circulation network) and different scales (plot, landscape), and discuss how agrobiodiversity contributes to the resilience of small-scale agriculture to different kinds of change.The first section of my thesis is based on the mapping of land use patterns, which allowed us to characterize the spatial and temporal dynamics of agroforestry and to analyze their socio-economic and physical drivers. I show that the emergence of this practice is linked to changes in farmers' strategies in response to various changes (declining fertility, price variations, population growth, etc.). Today, agroforests cover an important surface in landscapes, their spatial distribution is closely related to topography and they contribute to landscape heterogeneity.Taking the example of a village, the second section studies the local management of agrobiodiversity by analyzing the species composition of clove-based agroforests and their spatial organization, as well as farmers’ knowledge underlying these practices. I show that farmers manage a rich agrobiodiversity associated with multiple functions, and spatially organized according to topography, soil and species-environment interactions. Farmers' knowledge allows them to adapt to heterogeneous environmental conditions, to promote synergies between species and to make trade-offs between the different contributions provided to them by agrobiodiversity.Finally, the third section analyzes the way the farmers access to crop propagules and related knowledge. This part discusses in particular the role of exogenous plants and knowledge (from outside the study village) in agroforestry dynamics, and their implication in the resilience of small-scale agriculture. I show that to maintain and develop agrobiodiversity, farmers use their relational networks within the village and beyond. These networks allow them to observe other practices and, by mimicry, to change their own practices.The agroforestry dynamics described in this thesis highlight the adaptive capacities of smallholders’ farmers, a sine qua non condition for their resilience. Farmers’ local management of agrobiodiversity at the different scales reflects the holistic and integrative vision they have of their agroecosystem. Farmers’ knowledge and practices have great potential for the sustainable management of agroforests and for the restoration of degraded landscapes in these tropical regions. Based on a permanent dialogue between disciplines and between scientific and farmers' knowledge, this thesis is part of a perspective of co-construction of desirable and resilient agroforestry landscapes, and calls for the recognition of local practices and knowledge.; Les mosaïques paysagères des régions tropicales humides subissent depuis le milieu du 20ème siècle d’importants changements socio-écologiques qui menacent la résilience des agricultures familiales. Face à ces changements, les paysan.ne.s de certaines régions ont diversifié leurs systèmes agricoles en développant notamment des agroforêts (associations d’arbres avec d’autres espèces non pérennes et/ou des animaux, dans l’espace et dans le temps). Iels mobilisent pour cela la diversité végétale, cultivée ou non, et développent différents modes de gestion de cette agrobiodiversité. Ce travail de recherche vise à analyser ces dynamiques agroforestières au travers d’un cas d’étude situé au sein des paysages de la côte nord-est de Madagascar qui témoignent d’une évolution récente depuis une agriculture de subsistance reposant sur l’abattis-brûlis vers une agroforesterie complexe et multi-étagée. Articulée autour de trois parties, ma thèse discute des enjeux de résilience des agricultures familiales en analysant les modes locaux de gestion de l’agrobiodiversité et leurs évolutions en réponse aux changements.La première partie repose sur des travaux de cartographie des modes d’usage des terres qui ont permis de caractériser dans l’espace et dans le temps les dynamiques agroforestières, et d’en analyser les facteurs socio-économiques et physiques. Ces travaux montrent notamment que l’émergence de cette pratique est liée aux évolutions des stratégies paysannes en réponse à divers changements (baisse de la fertilité, variation des prix, croissance démographique entre autres). L’agroforesterie occupe aujourd’hui une surface importante dans les paysages, sa répartition spatiale est notamment liée à la topographie et elle contribue, avec la diversité des autres usages des terres, à l’hétérogénéité paysagère.En prenant l’exemple d’un village, la seconde partie étudie la gestion locale de l’agrobiodiversité en analysant la composition en espèces des agroforêts à girofliers et leur organisation spatiale, ainsi que les connaissances paysannes sur les interactions agrobiodiversité-milieu qui sous-tendent ces pratiques. Elle montre que les paysan.ne.s gèrent une riche agrobiodiversité qui est associée à de multiples fonctions, et qui est organisée spatialement selon la topographie, le sol et les interactions espèces-milieu. Les connaissances paysannes permettent de valoriser les conditions hétérogènes du milieu, de favoriser les synergies entre espèces, et de réaliser des compromis entre les différentes contributions que leur apporte l’agrobiodiversité.Enfin, la troisième partie analyse les modes d’accès des paysan.ne.s aux propagules de plantes cultivées et aux connaissances qui s’y rattachent. Cette partie discute notamment du rôle des plantes et des connaissances exogènes (extérieures au village d’étude) dans les dynamiques agroforestières, et leurs implications pour la résilience des agricultures familiales. Elle met en évidence que pour maintenir et faire évoluer l’agrobiodiversité, les paysan.ne.s utilisent notamment leurs réseaux relationnels au sein du village et au-delà. Ces derniers leur permettent par exemple d’observer les pratiques d’autres paysan.ne.s et de faire évoluer leurs pratiques par mimétisme.Les dynamiques agroforestières décrites dans cette thèse soulignent les capacités d’adaptation des agricultures familiales, condition sine qua non de leur résilience. Les modes de gestion locaux de l’agrobiodiversité spécifiques aux différentes échelles présentent un grand potentiel pour la gestion durable des agroforêts et pour la restauration des paysages dégradés de ces régions tropicales. Construite autour d’un dialogue permanent entre les disciplines et entre les connaissances scientifiques et paysannes, cette thèse s’inscrit dans une perspective de co-construction de paysages agroforestiers souhaitables et résilients, et appelle à la reconnaissance des pratiques et des connaissances locales.

International audience; Understanding how biocultural landscapes, as a result of human-nature interactions, have emerged and will evolve seem to us a fundamental prerequisite to better anticipate and understand the new ecological dynamics at work in Madagascar. This may help to better implement biodiversity conservation measures within and outside protected areas. In this contribution, we present several biocultural landscapes on the island, providing examples in contrasting ecological situations. These range from relatively old agricultural and agroforestry landscapes that continue to evolve today, which in turn make up relatively densely wooded landscapes without natural forests in an agroforestry landscape entirely formed by farmers. These cultivated landscapes, rich in cash crops, provide significant income to farmers, which makes such regions some of the most economically productive on the island. In contrast, the dry spiny thicket in the extreme south, provides an example with rather different dynamics. Here, the combination of the local cultural groups relying on agricultural activities (hatsaky or swidden agriculture) and hunting-gathering live in a rather ecologically extreme ecosystem. In the following sections, we present several biocultural landscapes and place each in its historical, biogeographical, human, and economic context.

The transition from shifting cultivation to perennial crop cultivation is observed in many regions across the tropics, to meet environmental and socio-economic challenges. In some areas, small-scale farmers have engaged in crop diversification through agroforestry, a practice that enables production for self-consumption and income, while coping with environmental constraints and heterogeneity. This is the case in a zone of Vavatenina commune of Madagascar, where the Betsimisaraka small-scale farmers have abandoned the traditional shifting rice cultivation on hills (tanety) in favor of agroforestry, mainly based on clove tree cultivation. These different tanety land uses shape complex agricultural landscapes that seems to result from various types of agroforests. Despite the major interest Vavatenina original landscapes may have from a sustainability perspective, its composition and spatial structure have not been studied so far. However, the high heterogeneity of these landscapes, at different scales (the plot, the village territory, the commune), raises methodological challenges. Similarly, scale related environmental factors, such as topography, slope and proximity to the road, appear to play on this heterogeneity, and thus required to be identified and their effect assessed. Our study applied an original method to meet this challenge by combining a landscape spatial analysis with a participatory mapping of agroforests. First, we described the composition and spatial organization of agroforestry at two scales, from that of agroforests in the landscape to that of species within agroforestry plots. Second, we analyzed the effects of topography and isolation level on the landscape and agroforests heterogeneity. We used a remote sensing method to quantify the proportion of the different tanety land uses, and analyze how agroforestry especially fits into the landscape and according to which environmental determinants. Then, we applied a participatory mapping method to study the spatial organization of species in 17 agroforests in a village of the study area. This method gave data on the species richness and the species associations in micro-zones related to topography. The results of the remote sensing analysis highlighted 10 different classes of tanety land uses, including more or less dense diversified agroforests, cloves tree and wood tree plantations. The results also indicated that the type of agroforests, the proportion of space they cover, and their insertion in the landscape differ very strongly between the localities of the study area. It seems that, while some areas have engaged massively in diversified and complex agroforestry, this is not the case in other nearby areas, where other less sustainable land uses seem to be favored (e.g. monoculture). The analysis of participatory maps showed that farmers managed between 8 and 22 species in their agroforests, and that they associated and spatially distributed these species according to topography. The combined results obtained with both methods contribute to better understand the heterogeneity of landscape and agroforests and its determinants. This approach would be of interest for supporting agroforestry transitions in other areas where farmers already engaged in such practices, to make a diagnostic of existing agroforestry and identify where and how support could be brought in priority.

The multi-dimensional diversification of agroecosystems, from the plot to the landscape scale, is known to be a key factor of social-ecological systems resilience. Agroforestry research especially brought considerable insights on this issue by documenting the socio-economic, agronomic and environmental outcomes of this type of practices. However, the drivers of agroforestry practices' heterogeneity and its spatial patterns remain poorly understood. This requires a diachronic perspective as the observed agroforestry systems often result from the gradual implantation of tree in pre-existing plantations, fallows, forests or pastures. This study addresses this issue through an original diachronic approach at the landscape scale, which contrasts from more usual static approaches focusing on cropping systems. We characterized the drivers of the observed heterogeneity of agroforestry practices and its spatial patterns in the landscape of a village located in the Analanjirofo region on eastern coast of Madagascar. In this locality, small farmers cultivated for 50 years varied perennial crops (clove, litchi and fruits, vanilla, coffee…) within different patterns including complex agroforestry systems. Analyses were conducted in 2016 on both qualitative and quantitative data collected through farmers' surveys on the following topics: i) the plant species grown in local agroforestry systems, ii) farms socio-economic characteristics, and iii) economic evaluation at plot level. A land-use map was built in 2016 through photointerpretation of drone and satellite pictures, and was compared with a map from 1966. The survey showed that a wide diversity of agroforestry practices currently exists on the locality regarding their plant species composition. Agroforestry accounted for 20% of the land surface in the study locality, resulting in a highly heterogeneous landscape mosaic. By merging the analysis of farmers' survey and the diachronic analysis of the land-use map between 1966 and 2016, we were able to give insights on the economic, demographic and geographic processes that led to the observed heterogeneity of agroforestry practices and their spatial patterns. These results raise perspectives to understand the processes involved in agroforestry evolution and expansion in Analanjirofo landscape over the past 50 years. Our results are relevant for supporting the orientation of social-ecological systems toward resilient trajectories.

A Vavatenina (Madagascar), la comparaison de la situation entre 1966 et 2016 a montré une forte évolution (0 à 20 % du territoire) des systèmes agroforestiers complexes (SAF). Issus de cultures pérennes en monoculture (café), la tendance est à la diversification (giroflier, litchi, vanille, autres fruitiers et arbres à bois de chauffe ou d’oeuvre, plantes médicinales). Le contexte agro-écologique et économique (accès aux marchés) et social influent fortement sur la structure des SAF et sur les stratégies paysannes. Ces SAF jouent un rôle croissant en termes de résilience des systèmes productifs face à des risques économiques croissants (volatilité des prix). On est globalement passé d’une résilience "apparente" directe (autoconsommation du riz produit) à une résilience "économique" indirecte basée sur plusieurs cultures de rente avec une profitabilité largement supérieure ce qui constitue une stratégie originale dans le contexte malgache d’incertitudes multiples., This study focus on agroforestry systems (AS) in the area of Vavatenina on the east coast of Madagascar, their evolutions over 50 years, their characteristics and their impact on the resilience of local farms. Comparing the situation in 1966 (Dandroy monograph published in 1973) with that of 2016 show a strong increase (from 0 to 20% of the territory) of complex agroforestry systems and their importance for ocal farms. From perennial crops in monoculture (mainly coffee), the trend is now to diversification and crop intensification on the same plot (coffee, clove, lychee, vanilla, other fruit trees, firewood or timber trees, medicinal plants...). The agro-ecological context (isolation, soils fertility...), as well as economic (access to markets) and social heavily influence the structure of local AS and farmers’ strategies from self-consumption to market oriented. AS play an increasing role in terms of resilience for production systems facing significant economic risks due to agricultural prices volatility. In addition to AS positive externalities on the environment, we observed a move from directly "apparent" resilience based on rice production for self-consumption to an indirect "economic" resilience based on several cash crops with much higher profitability in agroforestry systems which is an original strategy in the Malagasy context of multiple uncertainties.