Airborne and belowground phytotoxicity of invasiveAgeratina adenophoraon native species in Nepal

Volatile compounds from leaf litter of invasive alien Ageratina adenophoraare known to inhibit growth of native species in sub-tropical Asia, but there is not much evidence if the litter affects tree species. In particular, the relative importance of airborne inhibition versus belowground effect of invaded soil on tree species is rarely explored. We usedA. adenophorauninvaded and invaded soils to follow germination and seedling growth of a native Nepalese treeSchima wallichii(DC.) Korth. in the presence and absence of leaf litter ofA. adenophora. We also compared diversity of native species in the uninvaded and invaded sites in Nepal. We found thatA. adenophorainvasion is associated with lower native species richness and correlated with lower tree canopy cover. Invaded soil and the proximity ofA. adenophoraleaf litter decreased seed germination rate ofS. wallichii. Both invaded soil and leaf litter of the weed inhibitedS. wallichiishoot and root biomass accumulation independently of each other. As far as we know, this is the first study to report these two effects simultaneously. In conclusion, belowground effects ofA. adenophorainvaded soil and airborne effects of leaf litter have a potential to inhibit native tree regeneration in NepaleseSchima-Alnusforests. Maintaining high canopy cover and removing litter of the weed should be tested to control its invasion.