Invasion of alien species into new habitats poses serious threats to their vegetation and ecosystem processes. Austroeupatorium inulifolium, an invasive species, has been rapidly invading degraded grasslands dominated by Cymbopogon nardus, another invasive, in the Knuckles Conservation Area (KCA). Invasive plants with rapid growth rates and elevated leaf nutrient concentrations could alter decomposition process and nutrient release patterns. This study was aimed at studying the litter quality, decay rates and nutrient release patterns of Austroeupatorium and Cymbopogon. In situ litterbag experiment was conducted in less and highly invaded grasslands at KCA. Surface litter and standing litter (above-ground) also have been quantified to assess the contribution of C3 and C4 plants to soil nutrient pool.Litterbags (n=40) were prepared with air-dried litter samples of Austroeupatorium and Cymbopogon and were distributed in highly-invaded (HIG) and less invaded (LIG) sites (by Austroeupatorium). Litterbags were collected at different time intervals and chemically analysed. The decomposition rate was calculated using loss of litter biomass. The surface litter was estimated using randomly placed quadrates (0.0625 cm 2 ). Standing litter biomass was quantified by clipping quadrates (0.25 m 2 ) to the ground level. Contributions to aboveground litterfall by C3 and C4 plants were assessed. The results were statistically analysed and compared using Minitab 14.0.Higher mass loss was observed with Austroeupatorium litter than that of Cymbopogon in both less and highly invaded habitats. Austrosupatorium litter quality (in terms of N and P) is higher than that of Cymbopogon. Leaf litter of Austroeupatorium showed significantly lower C:N and C:P ratios compared to Cymbopogon. Nitrogen and phosphorus release patterns during decomposition found to be slow in both Austroeupatorium and Cymbopogon irrespective of their habitats. Austroeupatorium showed relatively higher decomposition rate throughout the study period compared to Cymbopogon. The surface litter and standing litter biomasses were significantly higher in HIG compared to LIG. In both habitats, C3 plants contributed more to the standing litter biomass than that of C4 plants. Austroeupatorium plants contributed more to the total C3 biomass in both LIG and HIG.The present results suggest that due to higher quality and decomposition rates of Austroeupatorium litter, the invasion may leads to changes in the soil nutrient pools and also their cycling processes. Long-term soil studies need to be carried out in order to investigate these findings further.

Austroeupatorium inulifolium Cymbopogon nardus Austroeupatorium inulifolium has become a noxious the mid-country of Sri Lanka. Highly degraded man-made grasslands dominated by Cymbopogon nardus in the Knuckles Conservation Area (KCA) have shown a high vulnerability for A. inulifolium spread. The present study was aimed at assessing the ability of A. inulifolium to alter soil nutrient turnover through changes in quality and quantity of litter inputs decomposition rates. Two grassland communities were selected based on the extent of A. inulifolium invasion viz., less-invaded (LIG) and highly-invaded (HIG). The surface litter and standing 2 and 2 in situ litterbag experiment was conducted using air-dried A. inulifolium and C. nardus litter separately and as a mixture to estimate decomposition rates and nutrient release patterns. The surface and standing A. inulifolium biomass in both communities. A. inulifolium litter decayed and released nutrients rapidly than that of C. nardus. The A. inulifolium invasion has the potential to increase the soil nutrient status through its release patterns. The results demonstrated the positive impact of A. inulifolium while highlighting the potential role of invasive species in degraded habitats.

A light loving invasive shrub, Austroeupatorium inulifolium has been spreading many land use types in the Knuckles Forest Reserve (KFR) in Sri Lanka, including man-made grasslands. In developing countries, there are limitations of using novel technologies to quantify and track the distribution of invasive species due to high costs and lack of facilities. This is a setback for their early detection and to introduce effective control measures. This pilot study attempted to map the distribution of A. inulifolium in man-made grasslands in KFR using high spatial multispectral images. Unsupervised, supervised and knowledge-based classifications were performed to quantify the spatial distribution of A. inulifolium in ERDAS Imagine. The results generated comparable results of the extent of area under A. inulifolium by using the unsupervised (108 ha), supervised (94 ha) and knowledge-based classifications (93 ha). They were 18, 15 and 15% from the total area selected for the study (622-646 ha), respectively. The results indicated the suitability of high spatial multispectral imageries in quantifying the spatial distribution of A. inulifolium. Further studies are recommended to investigate long-term changes in invasive plant population using multi temporal satellite data.

Abstract:Austroeupatorium inulifolium is aggressively invading many land use types in the Knuckles Conservation Area (KCA) in Sri Lanka. The Cymbopogon nardus dominated grasslands, often demarcated by native forests, are the most vulnerable. The present study quantified the soil seed bank and the standing vegetation of these highly invaded grasslands. Forest-grassland edge (FGE) has been identified as the starting point for this invasion, and therefore sampling was carried out twice at different distances from the FGE towards the grassland (0, 10 and 30 m). The soil seed bank showed high seasonality with higher abundance and richness in the wet season than in the dry season. Interestingly, the dry season soil seed bank was dominated by native species (78%) while the wet season seed bank was dominated marginally by exotics (52%), with the highest contribution from Austroeupatorium. The scarcity of tree seedlings was noticed during the study. Austroeupatorium and tree seeds showed decreasing trends from the FGE towards the invasive grassland, and were evident in the seed bank as well as in the standing vegetation. Despite similar trends, the soil seed bank and the standing vegetation of invasive grasslands showed low similarity in terms of richness and abundance due to the dominance of a single species.The results suggest that Austroeupatorium invasion has the potential to alter the existing vegetation in these highly degraded grasslands and influences their succession over time.