## 3 Results and Discussion
### Model Application and Limitation  
Understanding and quantifying the potential climate impacts on Chinese fir offers benefits to forest managers. Chinese fir is considered as one of the most important confer species in China, especially in southern China where timber is a major economic driver. Our work indicates that climate change will likely have a dramatic impact on Chinese fir growth and distribution. Forest managers at a local scale will need to adapt by developing management strategies that are best suited to future climates. At the provincial or national level, distribution patterns and forest productivity will assist forest policy-makers to generate more accurate and scientific-based policies. Information on both the distribution and productivity of Chinese fir is important for forest management. Although, impacts on plantation productivity under changing climate is critical for local managers, distributional information is of equal importance as it offers information on the potential suitable locations of planting Chinese fir in the future. Therefore, combined with other regional factors (e.g., economic limitation, local demands _etc._) the results of this work could contribute to the decision-making process by providing candidate plantation locations as well as their productivities, both of which will assist local managers better adapt the changing climate. The 3-PG model estimates the mean annual NPP of 930 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\), which is 10% higher than the national field data of 840 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\) provided by [43]. Since the NPP calculated in this study is for stands at their maximum growth potential or peak stand productivity (age 20 years), we believe that these estimates of Chinese fir are reasonable and correspond well to other studies. The NPP change predicted by 3-PG model provides a spatial and temporal outlook of climate change impacts on Chinese fir's carbon stocking. Although [PERSON] _et al._ (2014) [22] achieved similar results in terms of species geographic distribution and NPP estimates using PnET-II and MaxEnt models, a 3-PG based modeling approach, besides offering accurate carbon stocking predictions, is also able to provide more insights into the direct relationship between climate change, local forest industry needs as well as nation-wide afforestation strategies by providing more commonly used forest parameters (e.g., stand volume, DBH, stem density [29]; Figure 6). The use of 3-PG model combined with decision tree model has shown to be capable of predicting and mapping the impact imposed by climate change. Previously the model has been applied to species including lodgepole pine (_Pinus contorta_) and Douglas-fir (_Pseudotsuga menziesii_) in the Pacific region of North America [44,45]. In addition, by comparing the species distribution and NPP change maps from [PERSON] _et al._ (2014) [22], we believe that the results of this study provide a valid and analytical estimate of Chinese fir productivity under a changing climate and encourage the model application to other species and with more climate projections if possible. Compared to bioclimatic modeling approaches, which assume that there is an equilibrium between the species distribution and its current climate [46,47], physiological models such as the 3-PG model, utilize the physiological tolerance of the species in their predictions of the climate. For example length of daylight period, cloudiness, and other considerations are inherently dealt with in this approach. As with any modeling approach, assumptions and caveats are made and required. For the 3-PG model we applied the same species parameters across all climate projections and we did not consider any changes in species' intra genetic variability. Similarly with our exclusive focus on Chinese fir, we assumed that other species did not benefit from the changing climate and gradually out-competed Chinese fir.