The effect of excluding centuries-long ungulate grazing on unmanaged pollination in the Mongolian steppe

The capability of ecosystems to deliver services, such as agricultural production, in the future is largely dependent upon human land use.  Land use change resulting in habitat loss negatively alters ecosystem services.  In particular, services mobile organisms provide, such as insects and wild pollination, are negatively impacted.  Negative effects on wild pollination threaten the maintenance of local plant diversity and result in a productivity decline of insect pollinated crops.  We studied how the cessation of ungulate grazing in a traditionally grazed system would affect the community composition and abundance of forbs and insect flower visitors.  In the Mongolian steppe, between June and August, we observed and collected insect flower visitors in grazed and ungrazed paired plots.  We also recorded total flower abundance per species.  Using ordination and permutation tests, we found that forb community composition differed significantly between paired plots.  Overall flower abundance was greater in ungrazed plots ungrazed plots received fewer total visits.  The overall abundance increase in ungrazed plots was mainly driven Thymus gobicus, which had an increase of two orders of magnitude greater than the average.  Separate analysis by insect Order showed that only Hymenoptera community composition differed between paired plots.  Although exclusion of ungulate grazing resulted in an increase in overall flower abundance, the slight decrease in flower visitation resulted in fewer visits per flower to the community.  In our study, change in ungulate grazing patterns differentially affected the flower abundance of a few forb species and the visitation of only one insect order.