## 3 Results
### CARAIB Simulations for the Future
#### 3.2.3 Changes in Productivity and Distribution  
The projected species productivity and distribution are unsurprisingly dependent on the choice of the scenario for future climate, CO\({}_{2}\) atmospheric concentrations and potential CO\({}_{2}\) fertilization. Change in species distribution is derived from change in NPP between the end of the century (2080-2099) and the reference period (1980-1999). On a grid cell, a species disappears when its NPP goes down below the 100 g C m\({}^{-2}\) yr\({}^{-1}\) presence limit and appears when it outreaches this threshold. The impacts of the CO\({}_{2}\) atmospheric concentrations through RCP4.5 and RCP8.5 climate scenarios and of the CO\({}_{2}\) configuration prescribing the species response to increasing CO\({}_{2}\) were first analyzed averaging the vegetation model results obtained with the different climate model projections (Figure 6). The RCP8.5 scenario with a constant [330] (no CO\({}_{2}\) fertilization effect) is the most pessimistic scenario for the loss of species range. Considering the species ensemble, the model projects a range contraction of 23.6% but the species may lose up to 30% of their current distribution (_Musanga excopioides_). Assuming a CO\({}_{2}\) fertilization effect, the contraction remains under 5% of the current distribution. Regarding the expansion of species beyond their current distribution (assuming no dispersal limitation), the scenario assuming a CO\({}_{2}\) fertilization under RCP8.5 is the most optimistic (expansion of 55.6% considering the species ensemble). Expansion is at least 20% (up to 85% for _Guibourtia deneusei_) while it does not exceed 15% under a constant [330]. Reduction and extension of distribution are both less important under RCP4.5 (about the half). The simulations with a variable CO\({}_{2}\) mixing ratio but a downregulation of photosynthetic activity do not perform as expected, as the difference with simulations with a variable CO\({}_{2}\) mixing ratio and no downregulation is very limited. The differences lie in slightly lower projected expansion beyond the current distribution in the configuration with CO\({}_{2}\) downregulation: on average, species range may \"only\" increase by 28.1% and 50.4% under [down] RCP8.5 and RCP4.5 scenarios against 31.3% and 55.6% under [var] scenarios. If we consider the species average, the differences in the projected area expansion are 46.8% between the [330] and [var] RCP8.5 scenarios, 24.7% between the [330] and [var] RCP4.5 scenarios, 2.2% between the [330] RCP4.5 and RCP8.5 scenarios, and 24.3% between the [var] RCP4.5 and RCP8.5 scenarios. For area contraction, the differences between previous scenarios, respectively 22.6%, 11.5%, 11.1% and 0.5%, are less large. This suggests that the uncertainty in potential future distribution linked to plant response to CO\({}_{2}\) is, for most of the species, larger than the one related to the representative concentration pathway (considering here only two RCPs). The divergence in future species distribution due to climate model differences is also important. The projections of area contraction and/or expansion obtained with the different climates are presented in Supplementary S4. The highest inter-model disparity is met with the RCP8.5 scenario. The largest area reductions occur likely under the [330] RCP8.5: 47.8% of its current distribution for _Lophira alata_ (CanESM2), 46.6% for _Pericopsis elata_ (CanESM2), and 44.6% for _Musanga excopioides_ (MPI-ESM-LR), the first two being deciduous species. But, the [330] RCP8.5 scenario also presents the highest uncertainty. We observe a mean difference of 29.4% in the lost fraction (average for the 12 species) between extreme climatic scenarios. For instance, there is a difference of 43.2% in the lost area of _Lophira alata_ under CanESM2 (47.8% lost) and CNRM-CM5 (only 4.6% lost).