## 2 Materials and Methods
### The CARAIB Dynamic Vegetation Model
Soil water thresholds refer to available soil water in relative units, i.e., in terms of the variable (W-WP)/(FC-WP) where W, WP and FC are respectively the soil water content, the wilting point and the field capacity in mm. The model validation was conducted using CARAIB outputs obtained with the CRU historical dataset using both PFT and mean species-specific traits. To inspect the ability of the model to simulate the observed species distribution, the actual observations of individual tree species occurrence were superimposed over the simulated species NPP and we calculated the sensitivity (_Se_, proportion of presence data points correctly predicted by the model). To quantify the uncertainty linked to intraspecific trait variations, two additional simulations were performed replacing respectively the mean species foliage C:N ratio and SLA values by an extreme value (mean \(\pm\) standard deviation). The gross primary productivity (GPP) from a PFT-based simulation was compared to data at biome level of [PERSON] et al. (2018). An interesting asset of DVM is the potential to test several assumptions concerning the vegetation response to environmental changes, and specifically the CO\({}_{2}\) fertilization effect (as opposed to niche models which lack a direct mechanical connection between the physiology of the species and climate change), known as the increase of leaf photosynthesis with increasing atmospheric CO\({}_{2}\) mixing ratio. However, its long-term effect is uncertain given the interference of other processes on plant growth forcing them to reallocate available resources. Given these uncertainties, CARAIB was driven by climate scenarios under three CO\({}_{2}\) configurations:  
1. A constant atmospheric CO\({}_{2}\) mixing ratio of 330 ppmv ([330] configuration) in the hypothesis that there will be no fertilization effect due to nutrient limitation. Maintaining CO\({}_{2}\) concentrations constant in the model is indeed the only way to test this hypothesis since nutrient limitation in the model is only induced by the species C:N ratio which is a constant input;
2. An increasing atmospheric CO\({}_{2}\) mixing ratio ([var] configuration) according to the projections of RCP4.5 and RCP8.5 scenarios which respectively reach 538 ppmv and 936 ppmv in 2100. This, then, is consistent with the hypothesis that there will be a fertilizing effect and no nutrient limitation;
3. An increasing atmospheric CO\({}_{2}\) mixing ratio equal to those of the [var] configuration but accompanied by a downregulation of photosynthetic activity ([down] configuration) in an attempt to take the influence of decreasing nitrogen availability on the CO\({}_{2}\) fertilizing effect into account. Whereas the maximum carboxylation rate (V\({}_{\text{Cmax}}\)) for the first two is calculated as a function of foliage C/N and SLA ([PERSON], 2007), the third CO\({}_{2}\) configuration consists of a calibration of the photosynthesis based on empirical values of V\({}_{\text{Cmax}}\) and maximum rate of electron transport (J\({}_{\text{max}}\)) measured in free-air CO\({}_{2}\) enrichment (FACE) experiments following the meta-analysis of [PERSON] and [PERSON] (2018). These experiments were conducted mostly in temperate ecosystems. Their results are thus not directly transferable to the tropical species studied here. Nonetheless, we used them to construct an intermediate scenario of CO\({}_{2}\) fertilization, as a sensitivity test, since such experiments have essentially not been conducted up to now in the tropics ([PERSON] et al., 2018). Changes in NPP and biomass projected for the future under each climatic scenario and CO\({}_{2}\) configuration were calculated comparing CARAIB outputs averaged over the 2080-2099 period to the reference 1980-1999 values from the respective scenario.