The influence of goats on soil hydrological properties on semi-arid Bonaire
Invasive species are known to alter ecosystems all over the world. On the island of Bonaire, domestic goats (Capra hircus) were introduced in the 16th century. Today, their descendants occur on the entire island in the form of feral species and free roaming domestic animals, grazing and browsing on various plant species. Considering that goat trampling behaviour may cause topsoil structure amelioration and restriction of infiltration, it is likely that the goats on Bonaire increase the island’s susceptibility to erosion by mechanical disturbance. Bonaire likely had a climax vegetation of dry tropical forest in the past. However during the last centuries woody species and tall columnar cacti are diminishing and the vegetation on the island is largely transformed into a cacti-dominated scrubland with large expansions of bare soil.
A long term goat exclusion experiment in Washington Slagbaai National Park was set up 9 years ago. Recent research here has already shown that goat exclusion increases vegetation recovery. Apart from direct herbivory effects, the vegetation may also benefit from improving soil hydrological conditions resulting from eliminating goat herbivory and trampling effects. The aim of this thesis was to determine the role of goats on soil hydrological properties though conducting water-runoff simulations and infiltration tests. 9 year goat exclusion did not result in a difference in water and sediment runoff quantity. The litter percentage inside exclosures was higher, correlating with a lower soil temperature and higher soil moisture content. Where goats have access we found a higher amount of organic matter runoff, meaning that relatively more organic matter is retained inside the exclosure in case of a rain event. This shows us that goat exclusion is likely to play a role in the soil’s capacity to recover nutrient levels and soil moisture content.