## 5 Discussion
### Converging/Diverging Trends and Correlations between LOS and GSI
It has been observed that forest biomes and croplands are more frequently characterized by converging trends than non-forest biomes in the NH (Figure 4A,B), whereas non-forest biomes are more diverging than croplands and forest biomes (Figure 4F), suggesting biome-specific temporal changes in the coupled vegetation phenology and productivity. This was also confirmed by several studies at the regional scale ([PERSON] et al., 2016; [PERSON] et al., 2017; [PERSON] et al., 2018). [PERSON] et al. (2018) found that both SOS and EOS had location-dependent impacts on annual GPP. This is further supported by [PERSON] (2017) et al. who revealed that the inter-biome variations in annual GPP can be better explained by the variations in seasonal maximal photosynthetic capacity than LOS. In addition to the impact from ongoing global warming and natural climate variability, the relationship between vegetation phenology and productivity could also be affected by changes in both/either vegetation metrics induced by anthropogenic land use/cover changes (e.g., deforestation/afforestation, land clearing, irrigation and fertilization, and changes in land management practices) ([PERSON] et al., 2016; [PERSON] et al., 2018; [PERSON] et al., 2018; [PERSON] et al., 2018). Whereas, it could be assumed that changes in land management may also cause divergence between LOS and GSI (e.g., a change from one crop-type to another with different LOS/GSI characteristics), it is noteworthy that both converging trends and pixels with significant positive correlations between LOS and GSI are more pronounced for mixed forest than for the three natural forest biomes, which is also the case for croplands as compared to the three natural non-forest biomes (Figures 4A and 6B). These differences may reflect anthropogenic management in the form of fertilization and irrigation that could alleviate climatic constraints on vegetation growth influencing concurrently on both phenology and productivity ([PERSON] et al., 2016; [PERSON] et al., 2018). Moreover, it should be noted that areas of diverging trends type 2 in croplands are much smaller than it is the case for the three natural non-forest biomes (Figure 4F). This further indicates that anthropogenic land management is likely to be able to alleviate adverse climatic effects on vegetation phenology and productivity for both farming, and forestry and thereby weaken the observed diverging trends in LOS and GSI. Contrastingly, it could be expected that changes in land use (e.g., changes in crop types or land abandonment) could induce a differential response on LOS and GSI, as observed in [PERSON] et al. (2018), who revealed widespread changes in ecosystem functioning in the northern EA agricultural regions after the collapse of the Soviet Union in 1991 due to widespread agricultural land abandonment. Such extreme case of large scale land abandonment is likely to influence the results of divergent (converging/diverging) trends and changing correlations between LOS and GSI for major land biomes of the NH found here (Figures 3-8). Overall, this suggests the existence of complex relations and interactions between vegetation phenological changes and interannual variability of vegetation productivity induced by the interplay between both natural climate change and land management.