But while the economic cost of what the EU could lose in terms of trading is substantial, so is the price of the damages caused by alien pests and diseases. How do you put a price on a lost forest of ash trees?

“The main issue on the economics is that data is kind of scarce,” says Françoise Petter, former assistant director at EPPO. The costs and benefits of a closed system have not been calculated, and it is unknown whether losses incurred by a slower trading system would be offset by the preserved value of EU agriculture and biodiversity.