Native allelopathic plants: the potentially overlooked contributors to invasion resistance

Background/Question/Methods

Exotic invasions can suppress native diversity, and the invasibility of native communities can be affected by their diversity. Additionally, invasive success can be affected by the identity of constituent native species. In this context, we explored the potential of native allelopathic species to affect invasions in forests in southern China. The effects of species identity were integrated with the effects of species richness by comparing general relationships in relative abundance among native species and invasive species, to relationships among native species with measured allelopathic effects and invasive species. We studied spatial relationships among species in five forest parks within the Guangzhou city and within each park we randomly located twenty 1m² plots in the understories of forests dominated by Schima superba and Pinus massoniana. We recorded the cover of all native and all exotic species and the total species richness in all plots.

Results/Conclusions

Native species with the experimentally determined ability to allelopathically inhibit the most aggressive invasive weed in our system, Mikania micrantha, had little effect on the total diversity of other species. However, the presence of these allelopathic natives corresponded with far lower abundances of exotic species, and the abundance of allelopathic natives was negatively correlated with the abundance of invaders. We also found a strong negative relationship between understory diversity and the abundance of invaders. However, this relationship was not manifest in the presence of native allelopathic species. Our results suggest that allelopathic natives have the potential to resist exotic invasions, and that these species may alter the fundamental effects of species diversity during invasions.