The relative importance of different seed dispersal modes in dry Mongolian rangelands

Nomadic livestock husbandry is the main form of land use in Mongolia. Grazing impact on plant productivity has frequently been studied, but effects on dispersal modes are largely unknown. We assessed the relative importance of zoochorous dispersal for several species but focused on the dominant fodder grasses Agropyron cristatum and Stipa krylovii. We searched for seeds in the fur of goats and sheep, but also experimentally attached diaspores and monitored retention. Endozoochory was tested by incubating faecal samples under standardised conditions. Lab experiments on zoochory, anemochory and hydrochory supplemented the field studies.Seed retention in sheep fur was consistently good, and seeds stayed in the fur for hours or even days. Endozoochory proved to be of minor importance, while hydrochory is possible but depends on rarely occurring surface floods. Modelling potential dispersal distances showed that anemochory over larger distances is hardly possible. Thus, long-distance dispersal largely depends on epizoochory, as herds of sheep and goats cover up to 15 km per day and conduct long-range migrations in years of drought.In terms of seed retention potential, goats are relatively poor vectors, which is of concern due to their relative and absolute share of Mongolian livestock herds having dramatically increased in recent years.