## 3 Results
### Simulation Results of the Forest Ecosystem NEP of Zhejiang Province  
The forest ecosystem NEP total trend of Zhejiang Province from 1985 to 2015, based on the InTEC model after optimization, is shown in Figure 6. As shown in Figure 6, during 1985-2015, the forest NEP in Zhejiang Province showed an overall increasing trend, with an average annual increasing rate of 1.52 TgC-yr\({}^{-1}\). The forests in Zhejiang Province were carbon sources between 1985 and 1988. After 1988, the forests in Zhejiang Province gradually turned into carbon sinks, and the carbon sink  
Figure 5: Comparison between the model simulation net ecosystem productivity (NEP) and flux NEP at (**a**) the Tianmushan flux site, (**b**) the Anji flux site and (**c**) the Qianyanzhou flux site.  
speed began increasing rapidly. The annual average total NEP reached 26.38 Tg-C\(\cdot\)yr\({}^{-1}\) between 1989 and 2015.  
The spatial distribution of the forest ecosystem NEP is shown in Figure 7 (every 2 years). The forest carbon sink/source situation can be analyzed more intuitively in Figure 7. Before 1989, Zhejiang Province's forests were a carbon source, and among them, carbon source forests accounted for 36% in 1985. In 1989, 19% of the forests were still in the carbon source stage. By 1999, most of the forests had been converted into carbon sink forests; only 5% of the forests were still in the weaker source stage, and annual average NEP reached 381.76 gC\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\). Then, the carbon sink ability continued to increase, and further statistics indicated that more than 97% of the forests in Zhejiang Province were carbon sinks from 2000 to 2015. The annual average NEP reached 441.91 gC\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\), and the annual average NEP of coniferous forest and broadleaf forest were 416.36 gC\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\) and 632.47 gC\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{1}\), respectively.  
As shown in Figure 7, in the past 15 years, the areas with the largest forest carbon sink capacities in Zhejiang Province were mainly distributed in the mountainous areas in the east and southwest of Zhejiang Province, while the weaker areas were mainly distributed in the northeastern plains of Zhejiang Province. The changes in annual total NEP and NEP density of every city in Zhejiang Province during 1985-2015 are shown in Figure 8. The change of total annual NEP for each city ranged from 0.24 to 12.63 Tg-C\(\cdot\)yr\({}^{-1}\), and decreased in the following order: Lishui \(>\) Jinhua \(>\) Hangzhou \(>\) Hangzhou \(>\) Taizhou \(>\) Ningbo \(>\) Wenzhou \(>\) Quzhou \(>\) Shaoxing \(>\) Huzhou \(>\) Jiaxing (Figure 8a). The change of NEP density for each city ranged from 138.20 to 872.03 gC\(\cdot\)m\({}^{-2}\cdot\)yr\({}^{-1}\), and decreased in the following order: Ningbo \(>\) Jinhua \(>\) Taizhou \(>\) Lishui \(>\) Quzhou \(>\) Shaoxing \(>\) Hangzhou \(>\) Wenzhou \(>\) Jiaxing \(>\) Huzhou (Figure 8b).  
Figure 6: The time series of NEP of forests in the Zhejiang Province simulated by the InTEC model during 1985–2015.  
Figure 8: (**a**) Total NEP changes and (**b**) average NEP changes in different cities of Zhejiang Province from 1985 to 2015.  
Figure 7: The spatial distribution of forest NEP values in Zhejiang Province during 1985–2015.