The dynamics of Amazonian rainforest over long timescales connect closely to its rich biodiversity. While palaeoecological studies have suggested its stability through the Pleistocene, palaeontological evidence indicates the past existence of major expansions of savannah and grassland. Here we present integrated modelling evidence for a grassier Neotropics during the Last Glacial Maximum, congruent with palaeoecological and biological studies. Vegetation reconstructions were generated using the land processes and exchanges model, driven by model reconstructions of Last Glacial Maximum climate, and compared with palynological data. A factorial experiment was performed to quantify the impacts of fire and low CO₂ on vegetation and model–data agreement. Fire and low CO₂ both individually and interactively induced widespread expansion of savannah and grassland biomes while improving model–data agreement. The interactive effects of fire and low CO₂ induced the greatest ‘savannafication’ of the Neotropics, providing integrated evidence for a number of biogeographically relevant open vegetation formations, including two dry corridors (paths of savannah and grassland through and around Amazonia that facilitated major dispersal and evolutionary diversification events). Our results show a bimodality in tree cover that was driven by fire and further enhanced by ‘CO₂ deprivation’, which suggests biome instability in this region of climate space.

亚马逊雨林的长期动态与其丰富的生物多样性密切相关。虽然古生态学研究表明其在更新世的稳定性，但古生物学证据表明过去存在大草原和草原的主要扩张。在这里，我们提出了末次盛冰期期间更草的新热带地区的综合建模证据，与古生态学和生物学研究一致。植被重建是使用陆地过程和交换模型生成的，由末次盛冰期气候模型重建驱动，并与孢粉学数据进行比较。进行了因子实验以量化火灾和低 CO ₂对植被和模型-数据一致性的影响。火和低CO ₂单独和交互诱导大草原和草原生物群落的广泛扩张，同时提高模型-数据一致性。_{火灾和低 CO 2}的相互作用导致了新热带地区最大的“草原化”，为许多与生物地理相关的开放植被形成提供了综合证据，包括两条干燥走廊（大草原和草原的路径穿过亚马逊流域及其周围，促进了主要的扩散和进化多样化事件）。我们的研究结果表明，树木覆盖的双峰性是由火灾驱动的，并由“CO ₂剥夺”进一步增强，这表明该气候空间区域的生物群落不稳定。