## 4 Discussion
### Scientometric Analysis Insight: Role of Co-Citation Reference and Keyword Co-Occurrence Analysis
#### 4.2.4 Tree Growth Dynamics in Response to Climate Change and WUE  
Growth dynamics of a tree involve how trees respond to environmental signals over time, and how these responses are influenced by their genetic makeup and epigenetic factors [121; 122]. Similar to WUE, climate change has profound impacts on tree growth dynamics (TGD) of forest ecosystems. The understanding of interactions between TGD and WUE in response to climate change is critical for predicting forest productivity [87]. Tree growth is usually subject to various factors, such as temperature, precipitation, and atmospheric CO\({}_{2}\) levels [123; 124]. The ongoing climate change causes changes in these factors, resulting in complex responses in TGD. For instance, elevated temperatures caused by climate change can prolong the growing season in some forests [125; 126]. Meanwhile, elevated temperatures can also cause higher evapotranspiration rates, leading to water stress and decline in tree growth in some forest biomes [32]. Furthermore, elevated temperature also significantly influenced nutrient availability in the forest soil by encouraging decomposition of organic matter and soil nutrient mineralization. So, climate change also impacts nutrient uptake ability in plants and hinders the survival and productivity of forest ecosystems [127].  
A study conducted in a tropical forest has shown that increasing atmospheric CO\({}_{2}\) levels have resulted in higher intrinsic water-use efficiency (iWUE) [128]. iWUE is the ratio of carbon assimilation through photosynthesis to transpiration (water loss). An increasing iWUE trend should boost tree growth, but this behavior has not been consistentlyacknowledged. This inconsistency might be due to the negative impacts of elevated temperatures and varied precipitation patterns caused by climate change [32].  
Across different regions and forest types, the response of TGD and WUE may vary significantly. For instance, in humid subtropical regions of China, decline of tree growth rate was observed with an increase in iWUE; this might be due to negative effects of elevated temperature and altered precipitation patterns [129]. On the other hand, in arid and semi-arid regions, higher WUE due to elevated CO\({}_{2}\) may benefit tree growth more. Since these regions are typically water-short areas, an increase in WUE can have a positive influence on tree growth [130; 131]. Another study on boreal forests revealed that elevated temperatures and atmospheric CO\({}_{2}\) concentrations can enhance tree growth and iWUE [132]. The overall impact of climate change is still subject to the severity of temperature rise and changes in precipitation patterns.  
The impact of climate change on TGD and WUE is a complex topic and varies significantly over different regions and forest types. Although elevated atmospheric CO\({}_{2}\) levels can boost WUE, the cumulative effect on TGD is influenced by a combination of various climatic and environmental factors. Future research should focus on understanding the interactive effects of multiple climate change factors on TGD and WUE to better predict forest responses to climate change and ensure the sustainability of forest ecosystems.