# Simulating Forest Dynamics of Lowland Rainforests in Eastern Madagascar
## 3 Results
### Comparison of Model Simulations with Independent Field Data  
Following the model verification to the BTP forest inventory dataset (see Supplementary C), we compared the FORMIND model simulation to the ZNP forest as a model validation test site. While the character of ZNP forest differs slightly from BTP (see Supplementary A), the simulated forest approximates the structure of the ZNP forest overall, with per PFT stem counts per hectare, aboveground biomass (Tonnes C/ha), and basal area (m\({}^{2}\)/ha) \(R^{2}\) values of 0.95, 0.96, and 0.963 in 1:1 correlations, respectively (Supplementary A). The overall biomass falls within the runs and there is strong agreement with respect to the largest tolerant and intermediate tolerance shade classes.  
The most significant divergence in terms of forest structure occurs in the model's underestimation of the overall stem numbers and basal area (m\({}^{2}\)/ha); the aboveground biomass does not differ significantly. This is primarily due to the underestimation of stem numbers of sub-canopy and woody treelets by the model (PFTs 5, 6, 8, and 11). Basal area for large intermediate shade tolerance  
Figure 3: (**a**) Aboveground biomass time series for 50 stochastic FORMIND runs from bare ground (each 1 ha) in grey, with the average of those runs in black. The colored lines are averaged time series simulated biomass corresponding to the plant functional types (PFTs) keyed in the middle. Dot colors correspond to shade tolerance class, with shade tolerant PFTs in green, intermediate tolerance in blues, and shade intolerance in reds. The dots to the far right of the figure are the aboveground biomass values calculated from the Betampona (BTP) inventory plots in colors corresponding to PFT, with total in black; (**b**) This figure shows the stem number for each stem diameter class, with the BTP inventory plot data values as black dots, and the simulation values as a red line; (**c**) Measured aboveground biomass vs. simulated aboveground biomass (tC/ha) by PFT. Dot colors correspond to shade tolerance class, with shade tolerant PFTs in green, intermediate tolerance in blues, and shade intolerance in reds. Dot size corresponds to size class, ranging from canopy emergent (largest) to woody treelet (smallest); (**d**) Observed stem numbers in BTP vs. FORMIND simulated stem numbers. As with plot (**c**), dot size and color correspond to size class and shade tolerance; (**e**) Measured (BTP) vs. simulated basal area (m\({}^{2}\)/ha) per hectare. As with plots (**c**) and (**d**), dot size and color correspond to size class and shade tolerance.  
(FFT 2 and 4) trees was slightly overestimated by the model, but the degree was not significant enough to offset the overall underestimation (Supplementary A). Similarly, the largest shade tolerant group (FFT 1) and PFTs 2 and 4 were also overestimated by the simulation.  
To assess the differences in the comparative accuracies through time, Figure 4 shows successional groups related to light requirements for BTP and ZNP. It is interesting to note that there are relatively few shade intolerant trees overall in the forest, but especially in the initial colonization of the forest simulation. Initially, only a small number of shade intolerant trees colonize the bare ground, and the overwhelming majority of the biomass is from intermediate tree growth. In both forests (Figure 4), shade tolerant trees are underestimated by FORMIND, but both are within the margin of the range in biomass seen throughout the simulation. Intermediate trees are overestimated at both sites, though the simulation numbers do match the field numbers at around year 375 of the simulation, when shade tolerant trees account for the highest percentage of biomass and intolerant trees are at their lowest. However, these forests are both very old and have not been clear-cut in the past 400 years. Rather, the cause is more likely that a number of species were placed in the wrong plant functional groups.