Habitat determines the effects of wild ungulate grazing on soils: case studies from the Iberian Peninsula

Abstract Background and Aims The bidirectional relationship between plants and their soils can be disrupted by the influence of ungulate grazers. Indeed, herbivores affect plant productivity and above-ground community structure, and plants affect soil health and below-ground community structure. However, the effects of herbivory can be subtle and challenging to address experimentally, even in the case of relatively large ungulate grazers. We attempt to resolve this paradox and experimentally test effects of ungulate grazers in two case studies on the Spanish Iberian Peninsula. Methods At the two locations, we experimentally enclosed red deer ( Cervus elaphus ) at high and hyper densities for one year. We then compared, relative to non-ungulate controls, soil abiotic properties and biotic properties like bacterial and fungal community composition using DNA sequencing, to determine ungulate effects on soils. Results The results reveal that ungulates and their grazing had subtle effects on soil properties. Specifically, the presence of ungulates was tied to changes in bulk density and some chemical properties, but the only effects on bacterial or fungal community composition were tied to habitat. Differences in habitat use by the ungulates corresponded with increased bulk density and shifts in microbial community composition of the soil. Conclusions We conclude that over short experimental time periods, like one year, the effects of ungulate grazing may not be revealed. In fact, differences in plant community structure that are tied to abiotic soil properties may drive ungulate use of the land and moderate soil responses to the presence of ungulates.