Climate change is altering the distributions of species, which in turn causes shifts in the composition of plant communities. Specifically, rising temperatures should cause increasing relative abundances of heat-loving or heat-tolerant species (that is, ‘thermophilization’) and changes in precipitation should cause altered abundances of water-demanding species. We analysed millions of records of thousands of species and found that the plant communities in most ecoregions in North, Central and South America have experienced thermophilization over the past four decades (1970–2011). Thermophilization was fastest in ecoregions with intermediate temperatures and was positively correlated with warming rates within many biomes. Changes in the relative abundances of water-demanding species were less consistent and were not correlated with changes in precipitation, meaning that the drought sensitivity of some ecoregions may be increasing despite decreasing rainfall and increasing probabilities of drought. Climate-driven changes in plant community composition will affect the function and stability of New World ecoregions.

气候变化正在改变物种的分布，进而导致植物群落组成的变化。具体而言，温度升高将导致嗜热或耐热物种的相对丰度增加（即“嗜热”），而降水变化将导致需水物种的丰度发生变化。我们分析了成千上万种物种的数百万条记录，发现北美，中美洲和南美洲大多数生态区的植物群落在过去的四个十年中（1970-2011年）经历了高温化。在中等温度的生态区域中，嗜热化最快，并且与许多生物群落内的升温速率呈正相关。需水物种相对丰度的变化不太一致，并且与降水变化不相关，这意味着尽管降雨减少和干旱概率增加，但某些生态区的干旱敏感性可能会增加。由气候驱动的植物群落组成的变化将影响新世界生态区的功能和稳定性。