The circulation of seed among farmers is central to agrobiodiversity conservation and dynamics. Agrobiodiversity, the diversity of agricultural systems from genes to varieties and crop species, from farming methods to landscape composition, is part of humanity's cultural heritage. Whereas agrobiodiversity conservation has received much attention from researchers and policy makers over the last decades, the methods available to study the role of seed exchange networks in preserving crop biodiversity have only recently begun to be considered. In this overview, we present key concepts, methods, and challenges to better understand seed exchange networks so as to improve the chances that traditional crop varieties (landraces) will be preserved and used sustainably around the world. The available literature suggests that there is insufficient knowledge about the social, cultural, and methodological dimensions of environmental change, including how seed exchange networks will cope with changes in climates, socio-economic factors, and family structures that have supported seed exchange systems to date. Methods available to study the role of seed exchange networks in the preservation and adaptation of crop specific and genetic diversity range from meta-analysis to modelling, from participatory approaches to the development of bio-indicators, from genetic to biogeographical studies, from anthropological and ethnographic research to the use of network theory. We advocate a diversity of approaches, so as to foster the creation of robust and policy-relevant knowledge. Open challenges in the study of the role of seed exchange networks in biodiversity conservation include the development of methods to (i) enhance farmers' participation to decision-making in agro-ecosystems, (ii) integrate ex situ and in situ approaches, (iii) achieve interdisciplinary research collaboration between social and natural scientists, and (iv) use network analysis as a conceptual framework to bridge boundaries among researchers, farmers and policy makers, as well as other stakeholders. (Résumé d'auteur

The importance of seed provisioning in food security and nutrition, agricultural development and rural livelihoods, and agrobiodiversity and germplasm conservation is well accepted by policy makers, practitioners and researchers. The role of farmer seed networks is less well understood and yet is central to debates on current issues ranging from seed sovereignty and rights for farmers to GMOs and the conservation of crop germplasm. In this paper we identify four common misconceptions regarding the nature and importance of farmer seed networks today. (1) Farmer seed networks are inefficient for seed dissemination. (2) Farmer seed networks are closed, conservative systems. (3) Farmer seed networks provide ready, egalitarian access to seed. (4) Farmer seed networks are destined to weaken and disappear. We challenge these misconceptions by drawing upon recent research findings and the authors' collective field experience in studying farmer seed systems in Africa, Europe, Latin America and Oceania. Priorities for future research are suggested that would advance our understanding of seed networks and better inform agricultural and food policy

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IIResumo: As regiões do Médio e Alto Rio Negro, apesar de serem isoladas da malha de comunicação terrestre e das frentes de colonização, caracterizam-se por uma articulação cada vez mais forte entre a área florestal, a das comunidades, e a urbana, ou seja, as pequenas cidades ribeirinhas. Esta complementaridade, temporária ou definitiva, se traduz por uma expansão da agricultura periurbana. Propomos uma abordagem comparativa da diversidade agrícola entre o urbano e o florestal. Analisamos as relações entre formas de manejo dos espaços cultivados (superfícies, ciclo de uso e práticas), plantas cultivadas e redes sociais envolvidas no acesso aos recursos fitogenéticos. A análise mostra uma recomposição dos sistemas agrícolas com a permanência de uma alta diversidade agrícola, porém marcada por uma maior vulnerabilidade do sistema em decorrência da diminuição do tempo de pousio e da diminuição da força de trabalho disponível. No contexto urbano, as estratégias tradicionais de manejo dos recursos agrícolas se combinam a um outro objetivo, o do acesso à terra. A análise aponta para a necessidade de uma reflexão sistémica sobre as possíveis formas de conservação deste patrimônio biocultural.Palavras-chave: Amazônia. Agrobiodiversidade. Dinâmicas rurais urbanas. Etnobotânica. Abstract: Despite its isolation from land communications networks and colonization frontiers, the regions of the Upper and MiddleNegro River are characterized by increasing connectivity between rural or forest areas, pertaining to communities, and urban areas, i.e. small towns along the river. Population movement between these two poles, on a temporary or permanent basis, results in expanded periurban agriculture, in the context of new social and ecological arrangements. A comparative approach is proposed to cultivated plants diversity, based on a sample of 14 and 18 families in these urban and forest contexts. Relations among the diversity of managed spaces, biological diversity and social networks involved in access to phytogenetic resources were analyzed. The analysis shows a recomposition of agricultural systems with high crop diversity, at times higher than in the context of forests, albeit subject to more system vulnerability due to reduced fallow periods and available manual labor. In urban areas, traditional agricultural resource management strategies are combined with another objective, farmed lands access. This analysis also points out the need for reflection about the conservation of a biocultural heritage.

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