Endozoochorous Seed Dispersal by Yak and Tibetan Sheep on Alpine Meadow and Shrubland

The presence of seeds in livestock dung can alter the composition of aboveground vegetation. However, there have been few studies of the composition of the dung seed bank of Tibetan livestock on different vegetation types on the Qinghai-Tibet Plateau. The aims of this study were to identify the differences of endozoochorous seed dispersal in dung type and vegetation type and determine the relationships between the dung seed bank and aboveground vegetation in meadow and shrubland. We conducted experiments to assess the density and plant diversity of the seed bank of yak and sheep dung in meadow and shrubland. The dung seed density in Tibetan sheep dung from meadow sites was the highest (239.3 ± 13.8 seeds kg−1), and the number of species in yak dung from meadow sites was the highest. Among seasons, the livestock dung seed density was highest in November and the lowest in April. The species richness of the dung seed bank was higher in meadows than shrubland and higher in yak dung than that in Tibetan sheep dung only for shrubland. The dispersal of dung seeds has a greater impact on vegetation changes in meadows than shrubland, and the dispersal of seed in yak dung has a greater effect on vegetation changes than does dispersal in Tibetan sheep dung in shrubland. There were more monocotyledons in yak dung of shrubland (42%), whereas there were more dicotyledons in Tibetan sheep dung of meadow (45%). This suggests that yak and Tibetan sheep are complementing each other in their seed dispersal potential. Therefore, we recommend grazing more Tibetan sheep in the meadow and more yak in the shrubland on the Qinghai-Tibet Plateau.