COS 29-1
Effects of excluding aboveground herbivores of different body size on soil communities and processes in two vegetation types with different grazing history
Grazing is widely acknowledged as one of the major drivers of community composition and ecosystem functioning in grasslands. Most grasslands harbor a diverse assemblage of aboveground herbivores, ranging from ungulates over rodents to invertebrates. However, many ecosystem properties have been studied only in relation to large ungulates, ignoring the smaller-bodied and functionally different components of the herbivore guild. Recent research on aboveground-belowground and arthropod-plant interactions, however, is starting to show that smaller herbivores can also play important roles in ecosystem functioning. We present results from a study using size-selective fences to progressively exclude large (deer and chamois), medium (marmots and hares) and small (mice) vertebrate as well as invertebrate herbivores. Exclosures were erected in two vegetation types, which are the result of a different ungulate grazing history, in subalpine grasslands in the Swiss National Park. Short-grass vegetation originated where cattle used to rest before park establishment in 1914 and is more productive than the tall-grass vegetation where cattle used to graze but not rest. Today, short-grass vegetation is preferred by large ungulates for grazing. We studied how vegetation type and herbivore exclusion affected soil microarthropod and nematode communities, soil respiration and decomposition.
Results/Conclusions
Excluding different herbivores strongly affected nematodes, with higher abundance and a different community structure when all or all but invertebrate herbivores were excluded. Effects on soil microarthropod communities were limited to a reduction in springtail richness when all herbivore groups were excluded. Responses of soil respiration and decomposition to the herbivore exclusions depended on the vegetation type. These patterns were mostly related to changes in soil moisture, temperature or root biomass.
Grazing history affected many soil properties. Tall-grass vegetation had higher springtail richness, mesostigmatid mite abundance and a different oribatid mite community structure compared to short-grass vegetation, paralleled by higher root and microbial biomass. Bacterivorous nematode richness, soil respiration and decomposition rates were lower in tall-grass than in short-grass vegetation, linked to lower soil temperature.
Our results demonstrate that excluding herbivores of different body size elicited changes in soil communities and processes even after only a few growing seasons, and that small herbivores often had a larger impact than ungulates. The profound differences between the two vegetation types indicate that over centuries, ungulates can indirectly alter soil communities and functions through changes in vegetation. Our results indicate that the roles of differently sized herbivores warrant more attention in ecosystem research.