Controlling the abundance of invasive exotic wild boar (Sus scrofa) improves palm-tree conservation in north-eastern Argentina

Abstract

Linking management of invasive species to conservation outcomes is key to assessing program success. Wild boar (Sus scrofa) severely reduced the recruitment of Butia yatay palm trees, the main conservation value at El Palmar National Park, and was targeted for long-term control efforts. We integrated scattered and unpublished information to model the quantitative relationships among culling efforts (inputs), wild boar relative abundance (outputs), and damage extent (outcomes), indexed by ground rooting surface and yatay seedling mortality, and assessed how much cumulative effort was needed to achieve program targets. Park rangers culled wild boar by hunting with dogs and shooting rifles from stationary vehicles over 2004–2005. Local hunters hunted with dogs (2006–2011) and shot with rifles from elevated blinds (2006–2015). Linear regression of log-transformed variables showed that yatay seedling annual mortality and ground rooting declined exponentially over time as did wild boar abundance measured by hunting-based indices, which were significantly correlated. Limited ranger-led hunting efforts substantially reduced seedling mortality over < 2 year. Minimal seedling mortality (2.8%) and target levels of ground rooting (1.3%) were reached within 5 year of combined operations. When control efforts were interrupted for 6 months, ground rooting resurged while wild boar numbers increased. These results support the effort-outcomes principle and demonstrate the success of the management program in achieving conservation targets related to wild boar damage. Carefully structured and managed (organized) sport hunting of invasive wildlife may contribute to the sustainability of conservation programs.