Fifty thousand years of Arctic vegetation and megafaunal diet

Although it is generally agreed that the Arctic flora is among the youngest and least diverse on Earth, the processes that shaped it are poorly understood. Here we present 50 thousand years (kyr) of Arctic vegetation history, derived from the first large-scale ancient DNA metabarcoding study of circumpolar plant diversity. For this interval we also explore nematode diversity as a proxy for modelling vegetation cover and soil quality, and diets of herbivorous megafaunal mammals, many of which became extinct around 10 kyr bp (before present). For much of the period investigated, Arctic vegetation consisted of dry steppe-tundra dominated by forbs (non-graminoid herbaceous vascular plants). During the Last Glacial Maximum (25–15 kyr bp ), diversity declined markedly, although forbs remained dominant. Much changed after 10 kyr bp , with the appearance of moist tundra dominated by woody plants and graminoids. Our analyses indicate that both graminoids and forbs would have featured in megafaunal diets. As such, our findings question the predominance of a Late Quaternary graminoid-dominated Arctic mammoth steppe. By analysing plant and nematode DNA from sites all around the Arctic, it is shown that vegetation before about 10,000 years ago contained more forbs (non-graminoid herbaceous vascular plants) than previously believed, which changes our understanding about the functioning of the diverse northern ecosystem that existed at this time. Where the wooly mammoths roamed The picture is a familiar one in reconstructions of the Late Quaternary in the far north of Eurasia: abundant mammoths and other now extinct megafauna grazing on grassy 'mammoth steppe' tundra. Analyses of the vegetation of this period have been based mainly on fossil pollen data. This study uses a more direct approach — the analysis of plant and nematode DNA from sites all around the Arctic — and the results paint a rather different picture, questioning the predominance of grasses and suggesting that grass dominance may not be necessary to sustain a diverse megafauna. Before about 10,000 years ago the vegetation contained many protein-rich forbs — herby plants that are not graminoids (grasses, reeds and sedges) — that would have played a large part in supporting this diverse northern ecosystem. After the Last Glacial Maximum, however, the woody plants and graminoids dominated. The authors conclude that megafauna such as woolly mammoth, woolly rhinoceros, bison and horse may have been opportunisti