Nature management in coastal dune areas has gained momentum in Belgium. Management plans have been drafted, approved and executed for the Flemish nature reserves. In 1997, it was decided – after removal of shrub vegetation (Hippophae, Ligustrum), to reintroduce large domestic herbivores in the Flemish coastal dune nature reserve of the Westhoek. The original sand deposits of the reserve are slightly calcareous (2-6%). Today the decalcification boundary is situated between the surface and 25 cm deep.

In this research the impact on the soil of recently introduced ungulates i.e. Shetland ponies, Scottish Highlanders (cattle) and Konik horses was studied. The aim of the study was to investigate if treading by grazers causes compaction of the soil, if chemical soil parameters are already influenced by ungulate dung input into the system. To determine their impacts, both soil physical and chemical aspects were considered. The degree of compaction was determined by measuring the bulk density. The chemical parameters measured were the content of organic matter (OM), nitrogen (N), phosphorous (P) and potassium (K), the cation exchange capacity (CEC) and pH.

For the soil physical effect, the sampling design to determine changes in bulk density was to take core ring samples on trampled tracks with control samples taken adjacent to the tracks. The samples were taken at depths of 0-5, 10-15, 20-25 and 40-45 cm, the bulk density was gravimetrically determined. Comparison was made between treading effects in a low-lying regularly inundated (wet) area and in a grassy never inundated higher elevated area (dry).

To determine the changes in soil chemical properties due to ungulate dung, samples were taken at dung sites from the three animal species. The dung was categorized according to age of deposition (recent, medium or old) and five samples of each of the age category and of the three animal species were taken at depths of 0-5, 5-10 and 10-15 cm beneath the dung heap. The control samples were taken at a meter of the heap. The analysis of for OM, N, P, K, CEC and pH was done using standard soil determination methods.

There was a significant change in bulk density between paths and control areas (P<0.05). A higher organic matter content in the surface horizon of the soils of the wet area results in lower bulk density values compared to the dry area. With treading the effects on bulk density are greater in the wet than in the dry sites. The buffering effect of grass root sods in the dry zone may reduce the effects of compaction in this zone.

After preliminary analysis of the soils at 0-5 cm depth, chemical differences with dung input were not apparent according to the experimental design undertaken. Thus samples from 5-10 cm and 10-15 cm depths were not analyzed. K and K-saturation (K*100/CEC) showed a significant change between dung sites and the controls (P<0.05), the other parameters OM, N, P, CEC and pH did not show a clear trend with or without dung input. These results are in agreement with Berg et al. (1997). Profound chemical changes may not yet be apparent as the ungulates have been present in the system for less than three years and at a low stocking rate.

Inspections of the dung heaps themselves have shown the presence of a large number of associated dung fauna. Some of these such as Geotrupus species are capable of digging galleries and constructing broodchambers. Their influence on the soil is subject of ongoing research.