Abstract
1. Cattle grazing profoundly affects abiotic and biotic characteristics
of ecosystems. While most research has been performed on grasslands, the
effect of large managed ungulates on forest ecosystems has largely been
neglected. 2. Compared to a baseline semi-natural state, we investigated
how long-term cattle grazing of birch forest patches affected the
abiotic state and the ecological community (microbes and invertebrates)
of the soil subsystem. 3. Grazing strongly modified the soil abiotic
environment by increasing phosphorus content, pH and bulk density, while
reducing the C:N ratio. The reduced C:N-ratio was strongly associated
with a lower microbial biomass, mainly caused by a reduction of fungal
biomass. This was linked to a decrease in fungivorous nematode abundance
and the nematode channel index, indicating a relative uplift in the
importance of the bacterial energy-channel in the nematode assemblages.
4. Cattle grazing highly modified invertebrate community composition
producing distinct assemblages from the semi-natural situation. Richness
and abundance of microarthropods was consistently reduced by grazing
(excepting collembolan richness) and grazing-associated changes in soil
pH, Olsen P and reduced soil pore volume (bulk density) limiting niche
space and refuge from physical disturbance. Anecic earthworm species
predominated in grazed patches, but were absent from ungrazed forest,
and may benefit from manure inputs, while their deep vertical burrowing
behaviour protects them from physical disturbance. 5. Perturbation of
birch forest habitat by long-term ungulate grazing profoundly modified
soil biodiversity, either directly through increased physical
disturbance and manure input or indirectly by modifying soil abiotic
conditions. Comparative analyses revealed the ecosystem engineering
potential of large ungulate grazers in forest systems through major
shifts in the composition and structure of microbial and invertebrate
assemblages, including the potential for reduced energy flow through the
fungal decomposition pathway. The precise consequences for trophic
interactions and biodiversity-ecosystem function relationships remains
to be established, however.