Interactions between dung, plants and the dung fauna in a heathland in northern Italy

The influence of the insect fauna on cattle dung degradation and the development of a natural vegetal community was studied during three successive summers in a heathland in northern Italy. In 1992 and 1993, small (864 cm(2)) rectangular iron sheet frames were placed on the ground and assigned to three experimental groups: one (Control) had no dung, the second contained an artificially made (0.5 kg) dung pat protected with a mesh in order to exclude insects, while the third group contained dung which was colonised by insects. Above-ground primary production within the cages was collected at regular intervals from June to September. Dung addition had a huge effect on plant growth in both years (+29-31 %), in addition to this, in the first year, but not in the second, dung insects transferred to the soil an amount of organic material that also significantly stimulated (+14.5 %) the external growth of the plants. We suggest that the difference between 1992 and 1993 could have been determined by different numbers of grazing cattle in the study area: in consequence of this, we hypothesise that dung insects populations were larger and more active in the first year compared with the second. In 1994, the role of the insect fauna on dung degradation was investigated in greater detail. The total dry matter decrease in dung attributable to the activity of the insect community, after 20 days from dung deposition, was 18.4 % of the original dry weight; of that percentage, less than one third (5.8 %) was related to underground nesting (paracoprid) beetles. Earthworms were not active in the season when our survey was carried out. We concluded that the dung insect fauna can influence dung degradation and the growth of a natural plant community occurring on an acidic and impoverished soil, but that these effects are only of minor importance. This seems to be a consequence of the low densities of dung beetles in the study area and the absence of large-sized paracoprid and telecoprid scarabaeid species.