Barrier or bridge? Testing buffer zones in mitigating agrochemical spread and soil biodiversity shifts in Isabela Island (Galápagos)

The Galápagos Islands host a unique flora and fauna, including several endemic species. However, anthropogenic activities threaten the ecosystems of this archipelago, including the use of agrochemicals in agricultural areas to control the spread of invasive species. We investigated the effectiveness of buffer zones in limiting the transfer of agrochemicals and the spillover of soil fauna from agricultural ecosystems into protected habitats, thereby preserving the biodiversity of natural areas. To evaluate this, soil samples were collected on Isabela Island (Galápagos) from an agricultural area, the adjacent national park forest, and the buffer zone in between to determine the concentrations of agrochemicals and the diversity of soil faunal communities. Our results revealed a decline in agrochemical concentrations from the agricultural area toward the forest, confirming the buffer zone's role in preventing off-site contamination. We identified three distinct soil faunal communities associated with the agricultural area, the buffer zone, and the forest area. While the agricultural area exhibited the highest alpha diversity, the forest area harboured more taxa indicative of good soil quality. Ecological network analysis further demonstrated significant differences in species interactions across land-use systems. The agricultural area supported the most complex and dynamic interactions, while the forest exhibited a more specialised and stable network. In conclusion, our findings highlight the importance of buffer zones as agroecological mitigation strategies to preserve natural and protected habitats. We also emphasise the need to integrate biodiversity, species ecology and interactions to evaluate soil health. • The buffer zone limits agrochemical spread and faunal spillover in Galápagos. • Agrochemicals decline from agricultural fields to forests, protecting soil health. • Agricultural fields have higher diversity, while forests host key soil indicators. • Co-occurrence networks are more dynamic in the field and more stable in forest. • Biodiversity metrics and species ecology are key for soil health assessment.