Elevated CO₂ moderates the impact of climate change on future bamboo distribution in Madagascar

The distribution of bamboo is sensitive to climate change and is also potentially affected by increasing atmospheric CO₂ concentrations due to its C3 photosynthetic pathway. Yet the effect of CO₂ in climate impact assessments of potential changes in bamboo distribution has to date been overlooked. In this study, we proposed a simple and quantitative method to incorporate the impact of atmospheric CO₂ concentration into a species distribution modeling framework. To do so, we implemented 10 niche modeling algorithms with regionally downscaled climatic variables and combined field campaign observations. We assessed future climate impacts on the distribution of an economically and ecologically important and widely distributed bamboo species in Madagascar, and examined the effect of increasing CO₂ on future projections. Our results suggested that future climatic changes negatively impact potential bamboo distribution in Madagascar, leading to a decline of 34.8% of climatic suitability and a decline of 63.6 ± 3.2% in suitable areas towards 2100 under RCP 8.5. However, increasing atmosphere CO₂ offsets the climate impact for bamboo, and led to a smaller reduction of 19.8% in suitability and a potential distribution expansion of +111.6 ± 9.8% in newly suitable areas. We also found that the decline in climatic suitability for bamboo was related to increasing monthly potential evapotranspiration of the warmest quarter and minimum temperature of the warmest month. Conversely, the decreasing isothermality and increasing precipitation of the warmest quarter contributed to projected increase in bamboo-suitable areas. Our study suggested that elevated CO₂ may mitigate the decrease in climatic suitability and increase bamboo-suitable areas, through enhancing water use efficiency and decreasing potential evapotranspiration. Our results highlight the importance of accounting for the CO₂ effect on future plant species distributions, and provide a mechanistic approach to do so for ecosystems constrained by water.