## 3 Results
### The Role of Canopy Height Complexity for the Aboveground Biomass and Productivity  
The relationship between aboveground biomass (AGB), productivity (GPP), and the heterogeneity of canopy height complexity was investigated (Figure 5a). Here, canopy height complexity was described by the standard deviation of the RH95 of all GEDI lidar shots within 1 km\({}^{2}\). Hence, forests with a rather homogeneous canopy height had a low complexity, and forests with a heterogeneous canopy height had a high complexity. First, it could be seen that there was no clear trend in the data (Figure 5a). Only when looking at canopy height complexity was it noticeable that GPP increased from 0 to 45 Mg C ha\({}^{-1}\) a\({}^{-1}\) up to an AGB of 150 Mg odm ha\({}^{-1}\) when canopy height complexity was low. In forests with an aboveground biomass of larger than 150 Mg odm ha\({}^{-1}\) and a low canopy height complexity, productivity decreased again. Heterogeneous forest canopy heights, on the other hand, showed a positive trend and had productivity between 5 and 20 Mg C ha\({}^{-1}\) a\({}^{-1}\) for aboveground biomasses between 100 and 300 Mg odm ha\({}^{-1}\).  
The behavior could be described by different age structures (Figure 5b) of forests. Young forests (<40 years) with aboveground biomass up to 150 Mg odm ha\({}^{-1}\) showed high productivity and older forests (>40 years) with aboveground biomass above 150 Mg odm ha\({}^{-1}\) had reduced productivity. Additionally, considering the relationship between GPP, AGB, and NEE (Figure 5c), it can be noted that forests with the lowest productivities along the whole aboveground biomass range showed negative NEE values (carbon source behavior). Among the more productive forests, the highest positive NEE values (strongest carbon sinks) were observed for forests with low aboveground biomass (<150 Mg odm ha\({}^{-1}\)), while forests with high biomass (>150 Mg odm ha\({}^{-1}\)) tended to have neutral carbon balances.  
It can be concluded that, for the same aboveground biomass, early-successful forest stands have higher GPP values, stands with low canopy height complexities have higher GPP values, and stands with positive NEE also have higher GPP values. This suggests that a lower structural complexity indicates early-successful forest stands with carbon sink behavior.  
In addition, the relationship between AGB, GPP, and canopy height complexity was considered in terms of precipitation (Figure S3). For this purpose, the data were divided into low, medium, and high precipitation and compared. It was noticeable that in areas of low precipitation (Figure S3a), the aboveground biomass reached a maximum of 350 Mg odm ha\({}^{-1}\), while in medium (Figure S3b) and high (Figure S3c) precipitation regions, the aboveground biomass reached 500 Mg odm ha\({}^{-1}\) in some parts. Furthermore, the productivity of forests in medium precipitation areas was significantly lower. The maximum values here were around 40 Mg C ha\({}^{-1}\) a\({}^{-1}\); in comparison, productivity  
Figure 5: Relation between forest aboveground biomass (AGB) in Mg C ha\({}^{-1}\) and productivity (GPP) in Mg C ha\({}^{-1}\) a\({}^{-1}\). One point corresponds to a forest stand with an area of 1 km\({}^{2}\), whereby only areas containing more than 20 GEDI waveforms were considered. The points are colored (**a**) according to the heterogeneity of canopy height (SD of RH95) within this 1 km\({}^{2}\), (**b**) according to the mean age of the simulated forest within this 1 km\({}^{2}\), and (**c**) according to the net ecosystem exchange (NEE) within this 1 km\({}^{2}\), where positive values show a carbon sink and negative values show a carbon source. Mean forest age was calculated as the basal area weighted average of all tree ages.  
reached a maximum of 45-50 Mg C ha\({}^{-1}\) a\({}^{-1}\) in low precipitation areas and a maximum of 50-60 Mg C ha\({}^{-1}\) a\({}^{-1}\) in high precipitation areas.