## 4 Discussion
### Research Prospective and Practical Challenges in Climate Change and Forest WUE  
The research highlights a series of critical research and practical challenges that must be overcome to effectively advance the field of climate change and forest WUE. Currently, the scholarly work is mainly focusing on how climate change affects forest WUE by examining hydrological and biophysical dynamics, simulation and nutrient interactions, and hydraulic physiology across diverse forest types and regions (Figure 6). Nevertheless, further in-depth investigations are necessary to tackle the following challenges while linking the response of forest WUE to global climate changes. To do so, studies on the association between climate change and forest WUE will concentrate on how stable isotopes, radial growth, and sap flow patterns in species like Scot's pine and Norway spruce reflect carbon and water dynamics in terrestrial ecosystems, particularly in water-scarcity regions such as the Loess Plateau, and how these factors influence photosynthetic capacity, GPP, and NPP under varying water stress conditions; this can only be achieved through a multidisciplinary approach and integrated research strategies (Table 2). While climate change and forest WUE research covers a broad scope, we recommend the subsequent inquiries for future study, as a review identified insufficient work on these aspects (Box 1). We also propose that additional investigations are essential in Africa and Central American countries along with other less-studied regions worldwide, to gain a deeper understanding of the global ramifications of climate change and forest WUE, and their influences on ecosystem dynamics. Exploring how trees adapt their water-use strategies with rapidly changing climate and its influence on ecosystem health and carbon sequestration. It helps to identify vulnerable species and promote sustainable management practices to enhance resilience. In order to better understand and predict the effects of shifting environmental conditions on forest water dynamics, more research is required to create and update integrative models that link climate change and forest WUE by incorporating various climatic, physiological, and ecological indicators. **Box 1. ** Frontier topics. 1. How can effective forest-management practices and water-use strategies mitigate the impacts of extreme drought in various plantation schemes within water-limited regions globally? 2. How can adaptive forest-management strategies be improved (such as introducing xerophytic species, mixed and uneven age, species with high drought, fire, and pest resistance, species with cold waves, and heavy precipitation resistance) while initiating new afforestation projects to maximum resistance and resilience to extreme climate events? 3. How to assess the spatiotemporal variation in the response of forest ecosystem water-use efficiency to rapidly changing climates in various forest types, forest structures, management practices, and climate zones? 4. How does forest WUE of Chinese northern regions respond to climate change compared to southern regions, and what are the drivers of forest carbon and water cycle in these regions? 5. How do shifts in a forest's albedo caused by climate-related changes in vegetation cover influence the forest's WUE and its overall health? 6. What are the main drivers of climate change responses affecting forest ecosystem water-use efficiency in energy-limited and water-limited regions of the world? 7. How will Scot's pine intrinsic water-use efficiency (WUE\({}_{i}\)) and growth respond to various drought conditions in both monoculture and mixed forest settings, and what role do site-specific conditions such as fertility of soil, moisture contents, and topography play in modulating these responses? 8. How do variations in photosynthetic capacity influence water-use efficiency of forest ecosystems under different climatic conditions, such as heat stress and drought? 9.