Quantifying the magnitude of biological invasions using total biomass

Biological invasions rank among the greatest anthropogenic threats to global biodiversity and ecosystem functioning, but measuring and comparing their relative magnitudes across regions and taxa remains challenging. The absence of a unified metric hinders scientific advancement, public awareness, and policy development. We propose a simple, standardized metric to quantify and communicate the magnitude of biological invasions: total biomass of nonnative species. This metric approximates the amount of native biomass co-opted, displaced, consumed, or replaced by the populations of invasive species. We illustrate how this metric can be applied to different research themes and contexts such as temporal and spatial invasion dynamics, management strategies, and invasion forecasts. Although not a metric for impact, this magnitude will be useful to quantify the extent of impact of invasive populations. Total biomass can provide a common currency to assess the magnitude of biological invasions, facilitating comparisons, syntheses, and innovations across invasion science.