Allelopathy effects of invasive alien Ageratina adenophora on native shrub species of chir pine forest in the central Himalaya, India

Ageratina adenophora Spreng. is one of the most troublesome invasive species that has invaded various forest ecosystems in the central Himalaya. The chir pine (Pinus roxburghii Sarg.) forests in the region facing a high risk of invasion and loss understory diversity of native species. The present study comprehends the allelopathy effect of the invasive species A. adenophora residues bioassay (extract) and soil amendment against two co-occurring native shrubs viz Berberis asiatica Roxb. Ex DC. and Rubus ellipticus Sm. in a laboratory and natural forest conditions. Results revealed that a higher concentration (4% and 8%) of A. adenophora leaf, root and shoot extract have significantly inhibited (23% to 76%) and low concentration (1%) did not inhibit the seed germination, root and shoot length of B. asiatica and R. ellipticus. Furthermore, 8% (w/w) A. adenophora residue (leaf, root and shoot) amendments with the natural soil also showed significant inhibition effects (13% to 37%) on seedling growth and biomass of both the test species. Weekly A. adenophora leaf residue amendment showed higher inhibition in shoot elongation than root and shoot amendment during the experiment period. The study demonstrated that A. adenophora extract and residue amendment have strong allelopathic effects on woody shrub species and indicating allelopathy played important role in the successful establishment and rapid spread of A. adenophora in the understory of chir pine forests.