Temporal distribution of damages are critical determinants of the economic valuation of invasive species impacts

Invasions by non-native species can have large economic impacts that may be averted by prevention of species arrival via sanitary treatments, quarantine bans and inspection. The net value of such preventative measures can be evaluated by comparing the cost of prevention with the value of the damages that are prevented by species exclusion.  However the timing of expenditures on prevention are temporally offset from the timing of damages by the existence of invasion lags and the duration of spread into the invaded habitat. Furthermore, damages caused by some species are short-lived following their establishment while in other species, damages continue for an extended period or into perpetuity following establishment. This persistence of damages, along with interspecific variation in invasion spread and invasion lags have considerable impact on the present value of damages at the time of initial establishment because discounting of future damages back to the time of introduction diminishes the magnitude of impacts. Consequently, the benefit of prevention may be much greater for species that quickly cause damages than for species for which damages are more protracted or delayed.  These species-specific traits that affect the delay between arrival and the timing of damages should be accounted for when evaluating the benefit of excluding a species. We demonstrate this phenomenon using both a theoretical model and a case study of the three most damaging non-native forest pest species in the United States.