A new paper on the tundra came out in Nature. I had a small role in this paper, but found it fascinating.
Reconstructing the vegetation of the Pleistocene steppe by using frozen DNA instead of relying on pollen, it repaints the picture of the Arctic when the megafauna roamed the steppe. Instead of a grassy ecosystem, it was a colorful landscape of wildflowers.
More interestingly, the megafauna ate a lot of wildflowers.
Whether they preferred wildflowers over grasses or not is unknown, but a large proportion of the protein that they took in likely came from forbs.
And when the megafauna went extinct, the wildflowers declined in abundance.
The same thing happens when we pull grazers off of modern grasslands.
There isn't any evidence to support that something wiped out the forbs, which cascaded to wipe out the megafauna. Yet, the reduction of the high-protein forbs as grasses took over might have hastened their demise.
Willerslev, E., J. Davison, M. Moora, M. Zobel, E. Coissac, M. E. Edwards, E. D. Lorenzen, M. Vestergård, G. Gussarova, J. Haile, et al. 2014. Fifty thousand years of Arctic vegetation and megafaunal diet. Nature 506:47-51.