The influence of goats on soil erosion and vegetation in Arikok National Park, Aruba

Currently goats roam freely in Arikok National Park, Aruba. Case studies from around the world showed how livestock influence vegetation growth and physical soil properties. Livestock influences vegetation and soil by trampling and grazing. Trampling increases soil bulk density and this affects the water infiltration rate. The herbivory causes vegetation cover to decrease, which can lead bare soils to become vulnerable for wind and water erosion. Since 1970’s it is known that goats cause overgrazing in the area of Arikok National Park. In order to restore the landscape of the park, it is necessary to map the problem of freely roaming goats.

The aim of this research was to examine the current goat population and if goats affect the vegetation and soil in the national park of Aruba. To achieve this aim, the current goat population was estimated by counting the fresh pellets at nine research locations. The amount of pellets is then multiplied by 6.5 to assess the number of goats per km2. After the dung count, water infiltration rate was measured in six out of these nine locations. This was done with a mini disk infiltrometer. While measuring infiltration rates, other soil properties like soil texture, were observed at the locations. Furthermore, interviews were held with field experts for information about the impact of goats on vegetation.

Afterwards, the collected data was analysed with help of computer programs ArcGIS and SPSS. According to the goat dung count, the current goat population in the park is estimated at 1465 goats. This means 0.43 goat per hectare. During interviews with van Buurt and Smitz, it became clear that when the goat population in Christoffelpark, Curaçao was declined till 0.1 goat per hectare, the vegetation in the park started to regenerate.
The Kruskal Wallis test was used in SPSS to analyse the collected soil samples. It was tested if different groups of a variable (soil texture, vegetation cover and goat pressure) had a significant effect on water infiltration rates. There was no statistically significant difference in water infiltration rates between the different groups of the three variables

water infiltration rates did not significantly depend on differences in soil texture, vegetation. This means that cover or goat pressure classes. This may well be due to limitations in the study design. More extensive observations and more advanced statistical analyses that take into account interactions between aforementioned variables may still show negative effects of goats on soil and vegetation.