Exotic Invasive Plant Species Increase Primary Productivity, but Not in Their Native Ranges

Ecosystem net primary productivity is thought to occur near the maximum that abiotic constraints allow; but exotic invasive plants often correlate with increased productivity. However, field patterns and experimental evidence for this come only from the non-native ranges of exotic species. Thus, we do not know if this pattern is caused by exotic invasions per se or whether successful exotic species are disproportionately productive or colonise more productive microsites. We measured aboveground biomass in the field and in common gardens with five plant species in their native and non-native ranges. For all species combined, exotic invaders increased total plot productivity in their non-native ranges by 91% in the field, and by 107% in the common garden, but had much smaller or no such effects in their native ranges. Thus, exotic invaders appear to be a driver of increased productivity, not simply a passenger, but only in their non-native ranges.