Local communities often possess a detailed knowledge of their resources [1, 2] that potentially provides a valuable management base [3, 4] and a source of resilience to deal with change . Because of the potential of traditional ecological knowledge, sensu Berkes et al., and associated practices to sustain the natural base for livelihoods, researchers have tried to understand the pathways for the acquisition, maintenance, erosion, and spread of this type of knowledge. Previous research has noticed that traditional ecological knowledge is not uniformly distributed among resource users, and consequently, researchers have studied the sociodemographic characteristics that pattern intracultural distribution of knowledge. Researchers have found that age, sex, education, kinship, place of residency, social status, level of acculturation, and level of integration into the market economy, among others, correlate with intracultural variation in traditional ecological knowledge [7–10].
Researchers have based the systematic analysis of the pathways through which traditional ecological knowledge is transmitted on the seminal work of Cavalli-Sforza and colleagues . Based on generational differences and social relations between actors, this work considers three main pathways for the transmission of cultural knowledge: 1) vertical transmission, when information flows across individuals from different generations related through kinship [11, 12], 2) horizontal transmission, when information is transmitted between any two individuals of the same generation , and 3) oblique transmission, when information flows across individuals from different generations but not related through kinship [11, 14]. Recent research shows that the influence of each pathway changes across a person’s lifecycle .
While the idea that cultural knowledge flows through social relations is implicit in this line of thought, researchers have not engaged in a systematic analysis of the relations between the structure of social networks and the distribution of traditional ecological knowledge. This research gap is especially surprising given the well established finding from research on social networks highlighting that a node’s position in the network is a measure of the degree and type of information the node holds [12–14]. For example, in organizational settings, Brass and Burkhardt  have shown that the ability of a firm to capture knowledge is influenced by the position of the firm in the network. Similarly, Burt  shows how structural holes, i.e., the ability of an individual to bridge the gap among otherwise disconnected social groupings, bring new ideas to individuals because of their ability for assessing and comparing the different social groupings in which they are active.
The scant systematic research on the role of social relations on the transmission of traditional ecological knowledge has highlighted that information sharing among resource managers is based on trust and mostly occurs through kinship, friendship , or other social relations such as occupation  or ethnic background . But we know little about how structural characteristics that have proven central in the transmission of other types of information affect the transmission of traditional ecological knowledge. In this article we bridge research on the distribution of traditional ecological knowledge and research on social networks to investigate the relation between a person’s position in a network and her/his agroecological knowledge. We start by analyzing the structure of plant propagation material exchange networks and we then assess the association between a gardeners’ centrality in such networks and their agroecological knowledge. Research was conducted among home garden tenders in mountain regions of the Iberian Peninsula.
Our study focuses on networks of exchange of plant propagation material, mainly seeds, but also seedlings, bulbs, tubers, cuttings, suckers (hereafter germplasm exchange networks). We studied home gardens because they are considered in situ repositories of genetic diversity  and legacies of traditional gardening practices. Furthermore, both germplasm and knowledge are transmitted over generations [20, 21].
Based on Berkes et al. and Armitage , we use the term “agroecological knowledge” to refer to the cumulative body of knowledges, practices, and beliefs related to agronomic practices evolving by adaptive processes and handed down through generations by cultural transmission. We follow Calvet-Mir et al. and use the term “landrace” to refer to annual and biennial crops that have been continuously reproduced by gardeners during more than one generation (30 years or more, or 60 in the case of perennial crops and crops with vegetative reproduction) in the geographic area of study.
Researchers have previously described networks of germplasm exchange in different landscapes and socioeconomic conditions  highlighting the contribution of those exchanges to the conservation of agrobiodiversity in farmers’ fields [25–28]. For example, Boster  analyzed the social processes through which manioc (Manihot esculenta Crantz) stem cuttings are transmitted, sustained, and enhanced through networks of female linked by kinship ties; in a study in Peru, Ban and Coomes  found that home gardens agrobiodiversity is strongly tied to the number of seedlings and seed exchanges done by the gardeners; and Ellen and Platten  described germplasm circulation (or “the social life of seeds”) in British allotments. But, with some exceptions (see [30, 31]), those studies have not analyzed the link between the person’s structural position in the germplasm exchange network and his/her agroecological knowledge.