## 5 Discussion  
In this study, Mann-Kendall tests and Sen's slope were employed to examine the trends and abrupt changes in the LAI, FVC and GPP from 1982 to 2013 in the ARB. The results suggest that the LAI, FVC, and GPP exhibited strong spatial heterogeneity trends with different spatial patterns. The area demonstrating significantly increased FVC values (\(p<0.05\)), accounting for about 62.5% of the basin area, was larger than that presenting significantly increased LAI values (7.7%) and GPP values (16.3%). The areas of LAI, FVC and GPP that exhibited significant decreasing tends (\(p<0.05\)) accounted for 18.9, 2.0 and 10.5% of the basin area, respectively. The differences in the vegetation dynamics indicated strong spatial variations in the impacts of environmental factors on vegetation growth conditions on the one hand, and different degrees of vegetation greenness and productivity--influenced by the environment--on the other hand. However, some similarities did exist in the spatial patterns of dynamic trends of LAI, FVC and GPP from 1982 to 2013 in the ARB. For example, all three indexes showed an overall increasing trend in the Songnen Plain and a decreasing trend in the Mongolian part of the ARB. However, a much more significant increasing trend was found in the LAI and FVC over the Songnen Plain, and much more significant decreasing trends in LAI and GPP were found over the  
Figure 10: The spatial distribution of the regression coefficients for SM with the LAI (**(a–d)** shows the coefficients for Periods 1–4, respectively), FVC (**(e–h)** exhibits the coefficients for Periods 1–4, respectively), and GPP (**(i–l)** presents the coefficients for Periods 1–4, respectively) GTWR models for the four studied periods. Mongolian part of the ARB. In general, changes in the environmental factors of the Songnen Plain led to an increasing trend in the greenness and productivity of the vegetation in the region. Despite the overall increasing trend of vegetation indexes in the Songnen Plain, local Moran's I results showed that low-low aggregation of three indexes occurred in most areas of the region during the four studied phases. For LAI and FVC, the most significant changes in local spatial autocorrelation were recognized over the Sanjiang Plain, and the low-low agglomeration in the Sanjiang Plain decreased continuously. The different characteristics and stage changes in the spatial autocorrelation in the Sanjiang Plain and Songnen Plain, both of which are the food production bases of China, may be due to different planting structures. The PLSR results suggested that Pcp, Tmax, Forest, Pasture, SURQ, SW, and SM were the major factors affecting LAI, FVC and GPP in the entire study region. The spatial distributions of regression coefficients for the GTWR models showed that the relationships between vegetation indexes and climate factors varied with geography, and thus, exhibited significant spatial heterogeneity. In general, areas with low Pcp coefficients were found to be mostly distributed in the northeastern part of the basin, near the border of the Sanjiang Plain in China and in Khabarovsk Krai and the Jewish Autonomous Oblast in Russia. The areas with relatively high coefficient values were primarily concentrated on the borders of Mongolia, Russia, and China and near the Argun River Basin and the Shilka River Basin. A temperate humid monsoon climate predominates the eastern part of the ARB, while the Mongolian region and the Argun River Basin--as well as the Shilka River Basin in the headwaters region of the western ARB--are less influenced by the Pacific coastal monsoon and characterize a continental arid-semi-arid climate [34]. Therefore, the area near the Argun River Basin and the Shilka River Basin showed a high degree of positive influence of Pcp during all four phases, which was most likely attributable to the relatively dry climate of this region.