## 3 Results  
### Characteristics of Spatial and Temporal Changes in NPP  
#### 3.1.1 General Characteristics of NPP in the Study Area  
NPP was averaged over a 21-year period in northwest Liaoning to obtain the gradient of the one-way linear regression depicting the trend (Figure 3). The highest values were located in the southwestern sector of the research area, mainly in Huludao City, Lingyuan City, and Harqin Left Wing Mongolian Autonomous County in the southern part of Chaoyang City, where the annual mean NPP figures exceeded 400 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\). In this area, most of the vegetation cover types were forests and thickets with good vegetation growth, while the abundant precipitation and well-developed water systems in the southwestern region were favorable for vegetation growth.  
Most of the areas in the study area had medium values of NPP, including Chaoyang City, the eastern part of Fuxin City, Jinzhou City, Xinmin City, Faku County, Kangping County, and  
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Confidence Level** & **2001** & **2002** & **2003** & **2004** & **2005** & **2006** & **2007** & **2008** & **2009** & **2010** & **2011** \\ \hline High & 86.64 & 88.66 & 77.87 & 82.93 & 90.77 & 90.02 & 89.22 & 81.08 & 92.86 & 77.30 & 91.61 \\ Medium & 13.32 & 11.30 & 22.02 & 17.03 & 9.17 & 9.88 & 10.71 & 18.84 & 7.07 & 22.62 & 8.31 \\ Low & 0.04 & 0.04 & 0.11 & 0.04 & 0.06 & 0.10 & 0.07 & 0.08 & 0.07 & 0.08 & 0.08 \\ \hline
**Confidence Level** & **2012** & **2013** & **2014** & **2015** & **2016** & **2017** & **2018** & **2019** & **2020** & **2021** & \\ \hline High & 96.14 & 85.49 & 75.70 & 76.56 & 95.50 & 92.05 & 90.71 & 95.87 & 95.66 & 78.44 & \\ Medium & 3.78 & 14.41 & 24.17 & 23.36 & 4.42 & 7.85 & 9.17 & 4.02 & 4.22 & 21.44 & \\ Low & 0.08 & 0.10 & 0.13 & 0.08 & 0.08 & 0.1 & 0.12 & 0.11 & 0.12 & 0.14 & \\ \hline \hline \end{tabular}
\end{table}
Table 2: NPP data credibility classification.  
Figure 3: The spatial distribution of annual average NPP in northwest Liaoning Province from 2001 to 2021.  
Changtu County, with annual average NPP values ranging from 300 to 400 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\). Their values were 344.57 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\), 317.97 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\), 332.61 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\), 313.91 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\), 332.2 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\), 329.1 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\), and 340.74 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\). The vegetation cover types were mainly cultivated land, and the mean NPP figures for crops were generally smaller than those of forests and scrubs but larger than those of grasslands in China. The medium-value zones constituted a significant portion of the research area.  
The northern region of Chaoyang City and the western section of Fuxin City had low values of NPP, with annual means of less than 300 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\). Their deviation was about 30 gC\(\cdot\)m\({}^{-2}\cdot\)a\({}^{-1}\). These areas have poor water and heat conditions, and the land use type is mainly grassland with poor vegetation growth. Further, the developed urban areas in the southwestern region of Fuxin City may be more affected by anthropogenic activities, contributing to low NPP values. Overall, the mean annual NPP values in northwestern Liaoning varied considerably in the west, while the vegetation growth level was more similar to the rest of the region.