Preliminary study on the distribution of Austroeupatorium inulifolium in the Knuckles Conservation Area (original) (raw)
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Ceylon Journal of Science (Biological Sciences), 2014
Austroeupatorium inulifolium has become a ferocious invader over the years in many ecosystems in the wet zone of Sri Lanka, including the grasslands of the Knuckles Conservation Area (KCA). Two field studies were conducted to assess the impacts of Austroeupatorium invasion on the diversity and composition of the plant communities. In the first study, three habitat categories were identified: less-invaded grassland (LIG), highly-invaded grassland (HIG) and the forest-grassland edge (FGE) adjacent to HIG. In the second study, two transects were selected that run across the FGE bordered by less or highly invaded grasslands (FGE-LIG and FGE-HIG). At each community, 5 linear quadrats (12 m x 3 m) were laid parallel to the FGE at different distances away from the edge to the forest interior and the open grassland. Each quadrat was further subdivided into 3 quadrats. Three such transects were studied for each community. In both studies, the vegetation less than 2 m in height was enumerated. The stem density and abundance of Austroeupatorium were significantly higher in HIG and FGE compared to LIG. However, the plant community at FGE was less diverse than that of HIG and LIG. Tree saplings were observed only in the HIG, suggesting its favourable conditions for their establishment. The abundance of Austroeupatorium was markedly reduced towards the forest interior, suggesting that the FGE acts as a barrier against invasion towards the forest. The tree sapling abundance decreased from the forest interior towards the open grassland but the abundance was higher in transects bordered by HIG than by LIG. This suggests a facilitative effect on the forest tree regeneration potential under the Austroeupatorium canopy. The invasion may have led to improved microclimatic and edaphic conditions, which perhaps facilitated the tree seedling establishment and survival in the forest interior as far as 10 m away from the FGE. Current findings depict positive impacts of Austroeupatorium-invaded grasslands on the forest regeneration process. Therefore, it is time to explore the positive effects of exotic species, especially when they colonize highly degraded landscapes, rather than generalizing that all invasive species cause detrimental impacts on every landscape.
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.
Ceylon Journal of Science, 2018
A light loving invasive shrub, Austroeupatorium inuli-folium 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.
Non-native species are often abundant in the vegetation of forest edges, decreasing in abundance with distance into the forest interior. Regenerative strategies such as the seed rain and seed bank were expected to exhibit a similar pattern of decrease from the edge to the interior; however, this has been rarely investigated. Trends in abundance of the understory vegetation, seed rain, and seed bank of both native and non-native plant species from forest edge to interior at three different natural areas bordered respectively by a crop, a hay field, and a forest access road were quantified. Three 90 m transects were established perpendicularly across each of the three edge types into the forest interior. Twelve 3.14 m2 circular plots 5 m apart for the first 20 m and 10 m apart thereafter were established along each transect. We compared the abundance of all vascular plant species in the vegetation, seed rain, and the soil seed bank in these plots. Species richness of the vegetation, the seed rain, and the seed bank (native and non-native species combined) decreased from the forest edge into the interior. Sixteen non-native species were observed and were limited to 30 m from the forest edge. Out of these 16 non-native species, > 50% were found only in the seed bank. We observed different trends in abundance of native and non-native vegetation, seed rain, and seed bank for some species. Our study suggests that removing aboveground biomass of non-native species may not be the only thing to consider in non-native species management because of the high frequency of additional non-native species in the seed bank that are absent from the existing vegetation. In order to minimize non-native species, managers should eradicate seedlings of non-native species along forest edges before they mature and produce seed.
MORPHOLOGICAL PLASTICITY AND COMPETITIVE ABILITY OF AUSTROEUPATORIUM INULIFOLIUM
Invasive Alien Species (IAS) has become to a major threat to the natural and semi natural ecosystems of Sri Lanka. Among them, Austroeupatorium inulifolium (Asteraceae) is silently invading hilly areas in the wet zone of Sri Lanka. In the present experiment we tried to identify some eco-physiological traits of Austroeupatorium which could accelerate the invasive behavior. A pot experiment was carried out under glasshouse conditions where Austoeupatorium seedlings were placed in different densities (1, 2 and 4 seedlings per pot) as mono-cultures. Half of the pots were 'enriched' with nutrients (once per a week for 5 weeks) and the other half remained as 'un-enriched'. Plants were harvested, oven dried before taking the dry shoot and roots weights.