7 April, 2021
Invasion of the Polyphagous Shot Hole Borer Beetle in South Africa A Preliminary Assessment of the Economic Impacts
Martin P de Wit, Douglas J Crookes, James N Blignaut, Z Wilhelm de Beer, Trudy Paap, Francois Roets, Carmen van der Merwe, Dave M Richardson
Few economic assessments have been developed to inform national priorities on the management of high-impact, early-stage invasive alien species (IAS). Economic assessments are biased towards ex post assessments of the costs and benefits of control options and are in need of refinement to deal with potentially vigorous invaders with considerable uncertainty on spread and impact. The Polyphagous Shot Hole Borer (PSHB) beetle represents a potentially high-impact invasion in progress in South Africa. We approached the problem of PSHB invasion in South Africa through (i) interdisciplinary collaboration to reduce uncertainty in economic and biological parameters by defining robust ranges for model parameters and (ii) a simulation model to take account of dynamic mutualistic relations between the beetle and it's symbiont fungus. We modelled the potential social cost of a PSHB invasion on natural forests, urban trees, commercial forestry and the avocado industry. Our results indicate that the unmitigated baseline present social cost of $27.12bn in the case of a PSHB invasion in South Africa is in the order of 1% of the country's GDP, or expressed differently at around $50 per year per South African citizen (10-year modelling horizon using a discount rate of 6%). Most of the social costs in our model are for the removal of urban trees that die as a result of the PSHB, a result that corroborates well with findings in other regions where PSHB has invaded. We conclude that an ex ante economic assessment system dynamics model can effectively inform national strategies on IAS management. The disproportionately high impacts of a PSHB invasion on municipalities and private actors demands a revision of legislation and creation of policies pertaining to the management of biological invasions in South Africa.