Responses of Pine and Oak Species to Drought: A Bibliometric Analysis

Abstract

Pines (Pinus, with approximately 113 species) and oaks (Quercus, with around 435 species) are key genera that form forests across the entire Northern Hemisphere. These regions are often associated with seasonal drought and forest fires, worsening conditions due to climate change. In this study, we used bibliometric techniques to analyse research patterns regarding the drought responses of pine and oak species from 1977 to 2024. Our analysis relied on the Web of Science (WoS) database, focusing on publications indexed in both the Science Citation Index and the Social Science Citation Index. Our review included 104 studies examining 29 pine and 42 oak species in 58 combinations. Notably, many pine and oak species have yet to be studied. The most researched species include P. sylvestris (27 studies), P. halepensis (25 studies), and Q. ilex (27 studies). Geographically, the Mediterranean basins were found to be the most prominent areas of study. Much of the research originated in the United States and France, while recent contributions have come from China, Spain, and Canada. Research publications on this topic have increased since the 1990s, with noticeable peaks in 2008, 2011, and 2023. The journals contributing significantly to this body of knowledge include Tree Physiology, Forest Ecology and Management, and the Journal of Experimental Botany. Interestingly, while drought is a crucial aspect of plant ecology, much research has focused on physiological and botanical considerations. In the past two decades, there has been a marked increase in integrating climate-related variables with traditional physiological components and water management. The bibliometric analysis concluded that, at the genus level, the primary strategy of pines in response to drought stress is predominantly isohydric, while oaks tend to be anisohydric. This difference allows oaks to maintain gas exchange and carbon fixation, even for increased water loss. The shared occurrence of pine and oak species throughout the Northern Hemisphere suggests that proper management practices can be developed to promote the growth of one species through the other, especially by learning from post-drought recovery processes and succession.