## 4 Discussion  
### The Carbon Dynamics of the Amazon  
Here, it was demonstrated that an Amazon-wide determination of gross primary productivity is possible with linkage from GEDI lidar data and simulations from the individual-based FORMIND forest model. By fusing the data, we obtained a variety of forest parameters that were examined in terms of canopy height complexity. In this study, two main results were obtained. First, the structure-related relationship between aboveground biomass, net ecosystem exchange, forest productivity, and forest age was explored. Second, by linking the simulation data with the satellite data, an Amazon-wide carbon balance map was created. This map shows, among other things, that certain areas in the Amazon have already turned into a carbon source, while other areas are carbon sinks. Overall, according to this analysis, the Amazon can be considered to have a neutral carbon balance with a total NEE of \(-0.1\) Pg C a\({}^{-1}\). This NEE value is close to carbon neutrality. It should be noted that our net ecosystem exchange did not include direct carbon emissions from disturbances such as deforestation. The authors of [37] established a carbon balance in which South America, among other regions, was considered. In the carbon balance, the net carbon exchange was split into individual components. Emissions from fires in South America were estimated using two datasets--Global Fire Emissions Database Version 4.1 (GFED4) and Global Fire Assimilation System (GFAS)--that considered the area burned and the radiative power of fires, respectively. For example, emissions from fires in South America were 0.325 Pg C a\({}^{-1}\)[37]. If these emissions were included in our NEE calculations, the Amazon would be considered to be a carbon source. If deforestation and degradation continue in the future, the Amazon risks becoming a larger carbon source. Predictions that the Amazon may become a carbon source or that the decline in aboveground biomass will become irreversible are already supported by other publications. The author of [38] investigated the spatio-temporal dynamics of forest carbon in the Brazilian Amazon in the period of 2010-2019 using satellite data. [PERSON] et al. [38] observed that the changes in forest area in the Amazon have different causes, such as the extreme El Nino year in 2015 and drought in 2019 [38]. Aboveground biomass declines in the Brazilian  
Figure 8: Frequency distribution of NEE, determined in this study by combining GEDI and FORMIND data, compared to eddy flux data from GF-Guy and BR-Sa3. The data of this study are available in 1 km\({}^{2}\) resolution. Eddy flux data were averaged values from [PERSON] et al. [33] and [PERSON] et al. [34], and they are plotted as values (GF-Guy: 1.57 Mg C ha\({}^{-1}\) a\({}^{-1}\); BR-Sa3: 1.65 Mg C ha\({}^{-1}\) a\({}^{-1}\)). Amazon are caused by deforestation, forest fragmentation, forest fires, and mortality from climatic disturbances such as storms and drought [38]. Even though AGB losses in areas with intact forests were only 0.10 Mg C ha\({}^{-1}\) a\({}^{-1}\) in 2010-2019, [PERSON] et al. [38] drew attention to the fact that ongoing land-use changes, increasing climate extremes in the coming decades, and new Brazilian government policies may reduce the ability of forests to absorb carbon. They warned that achieving the goals of the REDD+ program will become more difficult. Although the Amazon is generally still considered as a carbon sink, there have been few studies that predicted that the Amazon is a carbon source [39]. Our NEE map (Figure 3d) showed many areas where the Amazon is already a carbon source. A similar behavior with a similar distribution could be seen in [40], where it was found that large parts of the Amazon are already so disturbed that they are sources of carbon; these are mainly the areas of the Arc of Deforestation in the southeast of the Amazon. [PERSON] et al. [41] also studied the Amazon's carbon footprint and saw the risk of the Amazon becoming a source of carbon.