Local food systems are growing, and little is known about how the constellation of farms and markets change over time. We trace the evolution of two local food systems (Baltimore County, Maryland and Chester County, Pennsylvania) over six years, including a dataset of over 2690 market connections (edges) between 1520 locations (nodes). Longitudinal social network analysis reveals how the architecture, actor network centrality, magnitude, and spatiality of these supply chains shifted during the 2012–2018 time period. Our findings demonstrate that, despite growth in the number of farmers’ markets, grocery stores, farms and restaurants in both counties, each local food system also experienced high turnover rates. Over 80% of the market connections changed during the study period. Farms, farmers’ markets, and grocery stores showed a 40–50% ‘survival’ rate, indicating their role in sustaining local food systems over longer time periods. Other actors, such as restaurants, had a much higher turnover rate within the network. Both food systems became more close-knit and consolidated as the center of gravity for both local food systems pulled away from urban areas toward rural farmland. Evidence of both growth and decay within local food systems provides a new understanding of the social networks behind local food markets.

当地的粮食系统正在发展，但人们对农场和市场群如何随时间变化知之甚少。我们追踪了两个当地粮食系统（马里兰州巴尔的摩县和宾夕法尼亚州切斯特县）在六年内的演变，包括 1520 个地点（节点）之间超过 2690 个市场连接（边缘）的数据集。纵向社交网络分析揭示了这些供应链的架构、参与者网络中心性、规模和空间性如何在 2012-2018 年期间发生变化。我们的研究结果表明，尽管两个县的农贸市场、杂货店、农场和餐馆的数量都有所增长，但每个地方的食品系统也经历了高周转率。在研究期间，超过 80% 的市场联系发生了变化。农场、农贸市场、杂货店的“存活率”为 40-50%，表明它们在较长时期内维持当地粮食系统的作用。其他参与者，例如餐馆，在网络中的流动率要高得多。随着当地粮食系统的重心从城市地区向农村农田转移，这两个粮食系统变得更加紧密和巩固。当地粮食系统增长和衰退的证据提供了对当地粮食市场背后的社会网络的新认识。