Native Plant Diversity Provides Resistance to Invasion by an Alien Species in Natural and Experimental Settings

It remains uncertain whether native plant diversity increases resistance to plant invasions at meaningful scales in nature due to contradictions between observational and experimental studies. In a field survey of 253 sites spanning 15 latitudinal degrees in China, we found that the relative abundance of the invader Alternanthera philoxeroides decreased with increasing native plant richness. Results from a 3-year field experiment and a 2-year mesocosm experiment further demonstrated that native diversity can suppress A. philoxeroides population growth (but not dominance) when natives precede the invader, or limit its population size when natives arrive after the invader. Insect herbivores and the soil biota were unlikely to influence diversity-based resistance in the field experiment, as their effects on both A. philoxeroides and native species did not change with native richness. Our results provide solid evidence that native plant diversity can provide resistance against plant invasion in natural ecosystems.