Global trends and thematic evolution of sap flow research in forests and woody plants

Abstract

Sap flow techniques are widely used in forest research to quantify tree water use and forest–atmosphere interactions across diverse climatic and ecological settings. Despite their increasing application, a quantitative understanding of how sap flow-based research has evolved in terms of publication trends, thematic development, and global collaboration patterns remains limited. This study presents a bibliometric analysis of global sap flow research published between 2000 and 2025, based on 2,572 peer-reviewed journal articles and reviews indexed in the Scopus database. Bibliometric performance indicators and science-mapping techniques implemented using Bibliometrix, Biblioshiny, and VOSviewer were employed to analyse publication trends, citation structures, leading contributors, collaboration networks, thematic evolution, and the intellectual structure of the field. Publication output increased steadily after 2010, accompanied by expanding international collaboration and increasing thematic diversification. Tree Physiology and Agricultural and Forest Meteorology emerged as the leading publication outlets, while the United States remained the largest contributor and China exhibited the most rapid recent growth. Keyword and thematic analyses indicate that sap flow research has evolved from a predominantly methodological discipline into an interdisciplinary field integrating plant hydraulics, ecohydrology, ecosystem water balance, drought responses, and climate-change research. Co-citation analyses further revealed strong linkages between methodological foundations, plant physiology, and ecosystem hydrology. By quantitatively characterizing the intellectual structure, thematic evolution, and collaborative landscape of global sap flow research over a 26-year period, this study provides a comprehensive benchmark for future investigations of forest water-use dynamics under changing environmental conditions.