## 3 Results
### Performance of Co-Citation Journals and Co-Citation Articles  
The co-citation network of journals pertaining to research domains of climate change and forest WUE is presented (Figure 5a). The findings of this analysis revealed that 192 research journals have disseminated articles on \"climate change and forest WUE\" with 298 cooperative links, with a modularity score of 0.718 and an average silhouette index of 0.930. The findings also identified \"Global Change Biology\" as the most prominently co-cited journal, accumulating a total of 662 citations (Figure 5b). Within the 20 leading co-citation journals, 8 are based in England, 6 in the USA, and 2 in Canada, Germany, and the Netherlands, and these journals collectively contribute to 42.52% of the total citations on the topic. The geographic distribution of the countries where the top 20 leading co-citation journals are published reveals that North America has 38.62% of the co-citation journals, while Europe contributes 61.38%. None of the top co-citation journals originate from any country in Asia, Oceania, South America, or Africa. Moreover >95% of the top 20 high-frequency co-citation journals are hybrid open access journals (Table S6). These journals encompass a wide range of disciplines such as forestry, ecology, botany, physiology, agriculture, meteorology, global changes, climate change, environmental studies, biogeography, management, and economics, demonstrating the multifaceted and interdisciplinary aspects of climate change and forest WUE research. Regarding the centrality metrics of the most influential journals, the _Journal of Hydrology_ achieved the highest centrality index of 0.56, leading the top 20 journals in this category (Figure 5c). Among these top 20 journals, 10 are associated with the USA, 4 with England, 3 with the Netherlands, 2 with Canada, and 1 with Germany. This also shows that journals from North America and Europe are performing their leading role in academic development. Moreover, all of the top 20 high-centrality co-citation journals are hybrid (Table S7). These journals are highly specialized journals, positioning them at the cutting edge of research in this area. Furthermore, the graphical placement of high-co-citation articles included 1063 nodes with 4058 links (Figure S1), demonstrating a modularity score of 0.672 and an average silhouette score of 0.824. The article \"Carbon Isotope Discrimination and Photosynthesis\", authored by [PERSON] et al., 1989 [PERSON] et al. (1989), published in the _Annual Review of Plant Physiology and Plant Molecular Biology_ in 2000, achieved the highest number of citations, totaling 252, followed by [PERSON] et al., 2010 [PERSON] et al. (2010), which presented the first global assessment showing that an ample increase in tree mortality was due to drought and heat stress. [PERSON] et al., 2013 [PERSON] et al. (2013), reveal that a significant increase in forest WUE was observed due to CO\({}_{2}\) fertilization effects in temperate and boreal forests. [PERSON] et al., 1982 [PERSON] et al. (1989), hypothetically clarified carbon isotopic composition in plants, and revealed stable isotopes in tree rings for paleoclimate reconstructions. (Table 1). Cluster classification of co-citation article analysis shows the following research themes. Cluster 0 (intrinsic water-use efficiency), Cluster 1(water-use efficiency), Cluster 2 (ecosystem water-use efficiency), Cluster 3(terrestrial carbon sink), Cluster 4 (carbon balance), Cluster 5 (severe drought effect), Cluster 6 (tropical forest), Cluster 7 (nutrient cycle), Cluster 8(gas exchange characteristics), Cluster 9 (drought disturbance), and Cluster 10 (structural change).