## 3 Results
### GPP Control Pathways of Different Fragmentation Levels  
A significant (\(p<0.05\)) difference in the mean CUP of forest landscapes in Zhejiang during 2000-2018 was detected among all fragmentation levels (Table 3). The highest and lowest mean CUP were represented by the INT and PAT forest landscapes, respectively, and there was no significant (\(p>0.05\)) difference in the mean CUP between TRA, PER, EDG, and INT. Moreover, the mean GPPmax of INT forest landscapes was significantly (\(p<0.05\)) higher than that for the PAT and TRA landscapes; no significant (\(p>0.05\)) difference in the mean GPPmax existed in forest landscapes in Zhejiang between TRA, PER, and EDG, or between PER, EDG, and INT. Similarly, a significant (\(p<0.05\)) difference in the mean CUP \(\times\) GPPmax of forest landscapes in Zhejiang during 2000-2018 was detected among all forest fragmentation levels (Table 3). The highest and lowest mean CUP \(\times\) GPPmax values existed in the INT and PAT landscapes, respectively, and there was no significant (\(p>0.05\)) difference in the mean CUP \(\times\) GPPmax between PER and EDG.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Fragmentation Categories** & **CUP (days)** & **GPPmax (g C m\({}^{-2}\) day\({}^{-1}\))** & **CUP \(\times\)GPPmax** \\ \hline PAT & 256.1 \(\pm\) 73.4 a & 8.7 \(\pm\) 2.2 a & 2339.4 \(\pm\) 949.7 a \\ TRA & 310.7 \(\pm\) 49.7 b & 9.6 \(\pm\) 1.6 b & 3041.2 \(\pm\) 737.1 b \\ PER & 329.8 \(\pm\) 28.5 b & 10.2 \(\pm\) 1.3 bc & 3369.1 \(\pm\) 548.5 c \\ EDG & 327.8 \(\pm\) 30.3 b & 10.1 \(\pm\) 1.3 bc & 3320.6 \(\pm\) 551.2 bc \\ INT & 332.9 \(\pm\) 28.1 b & 10.7 \(\pm\) 1.5 c & 3547.7 \(\pm\) 524.7 d \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparisons of mean CUP, mean GPPmax, and mean CUP \(\times\)GPPmax of forest landscapes in Zhejiang among different fragmentation categories during 2000–2018. The characters indicate the results of multiple comparisons between any two categories. PAT: patch forest, TRA: transitional forest, PER: perforated forest, EDG: edge forest, and INT: interior forest.  
Figure 3: Distribution of different control variables and their relative importance. (**a**) Spatial distribution of different control variables, (**b**) spatial distribution of their relative importance on annual GPP during 2000–2018, (**c**) comparison of relative importance among three control variables, and (**d**) pixel number percentages of three control variables for different fragmentation levels. PAT: patch forest, TRA: transitional forest, PER: perforated forest, EDG: edge forest, and INT: interior forest.  
Spatially, the mean values of CUP and GPPmax in the forest landscapes of Zhejiang during 2000-2018 both have high heterogeneities. The higher mean CUP values (>330 days) were generally found in the south and east parts of Zhejiang, while the lower mean CUP values (<210 days) were generally found in the north part of Zhejiang (Figure 4a). Among the regions with a high forest coverage, there was little difference in the mean CUP throughout 2000-2018, but the mean GPPmax during 2000-2018 presented obvious spatial variations. In particular, the highest values (>12.5 g C day\({}^{-1}\)) of the mean GPPmax during 2000-2018 were concentrated in dense forest landscapes in the east and northwest parts of Zhejiang (Figure 4b); however, the values of mean GPPmax during 2000-2018 were generally less than 10 g C day\({}^{-1}\) in the south dense forest landscapes in Zhejiang.