The Effects of Biome Stability During the Quaternary on Plant Diversity.

The distribution of global biomes has changed during Earth history in response to changes in the climate conditions. We aimed to study how climate change during the Quaternary, a period characterized by periodic transitions between glacials and interglacials and a cooling trend, influenced the expansion of biomes and biome stability. We further studied the hypothesis that biome stability can explain current patterns of plant species richness. We used machine learning and correlative models, current bioclimatic conditions, and an observation-based biome map to model the current global biome distribution. Then, we drove the model with bioclimatic conditions for the last 2.6 million years at a 1000 year temporal resolution to obtain global climate-driven biome suitability maps for this period. Our results indicate that during the study period, biomes were stable in large parts of tropical forests, deserts, boreal and temperate forests, while northern Europe, northern and central America were core areas of biome change. Biome shifts in the far North were caused by regular transitions between boreal vegetation and ice. We analyzed the relation between biome stability and current plant species richness. In tropical rainforests, species richness was positively related to biome stability, but globally the overlap between stable biomes and centers of high species richness was weak. Our modeling framework provides important insights into the stability of biomes during the Quaternary. We suggest that biome stability cannot fully explain species richness, indicating that other factors such as fire or spatial heterogeneity are important. Even though our approach is based on climate only, it is appropriate for further studies due to its general applicability to and spatial and temporal resolution and high computational performance.