Does Ageratina riparia Affect the Regeneration of Forest Species in Disturbed Montane Forests in the Knuckles Forest Reserve

Abstract

The invasive herb Ageratina riparia (Regel) R. M. King & H. Rob. (Asteraceae) which is anoxious weed in many countries including Hawaii, New Zealand and Australia is spreadingrapidly in the forest gaps, edges and along the footpaths inside disturbed montane forests inKFR. Since A. riparia forms a thick mat in the ground layer of montane forests, its spread canhave a detrimental effect on the establishment of seedlings of forest species. Six forest gapsand four footpaths inside a disturbed montane forest were sampled to investigate the effect ofA. riparia on the regeneration of the montane forest species. Soil moisture content, soil rootdensity and canopy openness were also determined. Soil seed bank experiments were carriedout during wet and dry seasons. The percentage cover of A. riparia decreased significantlywhen moving away from the centre of the footpaths (P=0.001, F=9.78, 0 m=62.5%, 5m=6.9%, 10 m= 11.3%) and the forest gaps (P<0.001, F=25.54, centre=75%, edge=19.75%,5 m away=0.17%) into the forest interior. The mean density of seedlings of forest speciesshowed a negative relationship with percentage cover of A. riparia. The mean density (forestgaps; centre=2.8m-2, edge=7.5 m-2, 5 m=5.8 m-2, footpaths; 0 m= 2.65 m-2, 5 m=6.5 m-2, 10m=6.12m-2) and the species diversity of forest species decreased with the increased A. ripariacover. The root density and root moisture content of forest species was lower in areas wherethe root density of A. riparia is higher. The soil moisture content in all the locations wasnearly equal at all distances from the centre of the gaps and footpaths into the forest (~2). Thecanopy openness was higher in the forest gaps than the footpaths (P<0.001, F=27.48).According to the results, growth and establishment of A. riparia is determined by the qualityof light. Seedling emergence of A. riparia from soil seed bank was higher during the dryseason than the wet season. Lower number of forest seedlings emerged in the locations wherehigh emergence of A. riparia seedlings was recorded. However according to the statisticalanalysis there was no relationship between the number of A. riparia seedlings and theseedlings of tree and shrub species that emerged from the soil seed banks (forest gaps; R2=0,Footpaths R2=0.005). Since native forest species including Psychotria zeylanica andSymplocos cochinchinensis showed high seedling densities even with high A. riparia cover.They can be used to restore disturbed submontane forest patches invaded by A. riparia atKFR.