IMPACT OF Chromolaena odorata INVASION ON RICHNESS AND DIVERSITY OF VEGETATION IN PASTURE AREA. Muhammad Rusdy ABSTRACT

Transcription

1 IMPACT OF Chromolaena odorata INVASION ON RICHNESS AND DIVERSITY OF VEGETATION IN PASTURE AREA Muhammad Rusdy 1 Laboratory of Forage Crops and Grassland Management Faculty of Animal Science Hasanuddin University, Indonesia Corresponding muhrusdy79@yahoo.co.id ABSTRACT Chromolaenaodorata (L.) R.M. King and H. Robinson, an exotic plant from tropical America has invaded large of tropical and subtropical areas in the world. This study investigated the impact of C. odorata invasion on plant number, richness, diversity and evenness of vegetation in overgrazed pasture in Maiwa ranch, Indonesia. As determined by various ecological indices, there were higher plant number, species richness, diversity and evenness in invaded areas than in non-invaded areas. All plants found in un-invaded areas also were found in invaded areas, howeversome plants only restricted in invaded areas. The higher species diversity in invaded areas might be attributed to enhanced growth of low palatability of species growingunder C. odorata stand and escaping of growing plants from livestock trampling during grazing under Chromolaena stand. Key words: Chromolaenaodorata invasion, plant number, richness, diversity, evenness INTRODUCTION A major constraint to livestock production in developing countries is the scarcity and fluctuating quantity and quality of year around forage supply. During the rainy season, tropical forage species grow at very fast rates, with forage yields often exceeding animal requirements. If not cut or fed to animals, during the dry season this forage becomes fibrous and lack in most essential nutrients which required for improved microbial fermentation and performance of animals. In densely populated country such as Indonesia, the lack of forage supply are aggravated by the high conversion of grassland to cash crop land and invasion of alien weeds into grassland area. Invasive alien plants known to posses many physiological and morphological traits that help them to invade successfully in new habitats. Since introduced to Indonesia in the turn of the twenty century, Chromolaenaodorata invasion has transformed forest, grassland and savanna ecosystems. Its fast growing, highly competitive for nutrients and allelopathic traits making this weed can be forming a dense stand that reducing grazing area and lowering productivity of forage species. Its bitter tasting and high levels of nitrate and alkaloids(sajiseet al., 1974;Panco and Plucknett, 1971) making this plant is avoided by livestockand increasesits competitiveness in grasslandarea.in Maiwa ranch Indonesia, during dry season, grassland heavily invested by Chromolaenaiscommonly overgrazed and many livestock were dead because of starvation. Exotic species invasion and overgrazing can drive declines in biodiversity and grassland ecosystem functioning (Isbell and andwilsey, 2009). Biodiversity is known to 140

2 have a stabilizing effect on productivity through asynchrony between species.in the long term, productivity of grassland was higher in higher diversity than in lower diversity ecosystems (Tilmanet al. 2001).Overgrazing decreases plant diversity, changes the botanical composition of the sward and can lead to the weed invasion (Metera and Sawoski, 2010). Invasion and spread of Chromolaena.odorata in overgrazed natural grassland generally making ecosystems unstable as species richnessand diversity decline (Goodal and Zacharias, 2000; Nolubabalo,2013), however Callaway et al. (2000) reported that species with certain traits have the potential to preserve plant diversity in overgrazed plant communities. There is a lack of study concerning impact of Chromolaenaodorata invasion on vegetation characteristics in overgrazed pasture. The present study examine the impact of Chromolaenaodorata invasion on richness and diversity of vegetation in pasture area. Study site MATERIALS AND METHOD The experiment was conducted during the dry season in a pasture owned by the Faculty of Animal Science Hasanuddin University. The site was located at Maiwa, Enrekang regency South Sulawesi Indonesia from July to November 2012 (3 o S, 119 o E) at about 1300 m above sea level. The climate of the area is tropical monsoon characterized by one rainy season (November to June) and one dry season (July to November). The annual average rainfall was 2426 mm with a daily average temperature of approximately o C. The soil texture was silty clay loam. The area was heavily infested by combinations of Chromolaena, Stachytarphetajamaicensis, Borreriasp and some other weeds and herbage species. Data collection Field study was conducted between July and October Maiwa ranch occupies about 200 ha of land, most of them have been invade by Chromolaenaodorata since 30 years ago. Chromolaena stand distributed over the ranch that may attained covering about 40%. In this study, 30 pairs of adjacent 2 x 2m vegetation plots, viz.chromolaenadominant/invaded plots and Chromolaena free plots, were sampled. In each vegetation type, one quadrat(1 x 1 m) was placed randomly and density, frequency and cover of each species inside the quadrate were calculated. The uninvaded plots was chosen as to have as similar site conditions as possible to the invaded plot, which could be assumed with reasonable certainty due to the invaded plot being located in close proximity to the invaded plots (distance 2-3 m). Methods used to calculate ecological indices In this study, ecological indices measured were richness, diversity and evenness Measurement of richness: 1. Margalef s index (Margalef, 1958) Margalef s index = (S - 1) /ln N Where: S = total number of species, N = total number of individu in the sample 2. Menchinick s index richness, D (Whittaker, 1977) D = S/V N 141

3 Where: S = number of species in the sample N = total number of individuals. Measurement of diversity: 1. Diversity (Shannon-Weiner Index) = Sum (pi) x ln (pi) Where: pi = proportion of total sample represented by species i 2. Simpsom s Diversity Index (D) ( Where: n = total number of organism of a particular speces N = total number of individuals of all species Measurement of evenness (Pielou, 1966): 1. Pielou s index of evenness = H / ln S Where: H = Shannon Wiener diversity index S = total number of species in the sample Statistical analysis In this study, statistical analysis were conducted using software programme SPSS ver.17. For determining the significance of paired treatment (invaded and control), student s t test was used. RESULTS AND DISCUSSION A total of 29 species plants, most of them were alien plants were collected from the area during the study. All species of plants found in un-invaded areas also were found in invaded areas, however there were some species that only restricted in invaded areas. In contrast to widely reported, invasion of Chromolaenainto overgrazed pasture highly increased its richness and diversity index (Table 1). Table 1. Number of species, richness, diversity and evenness index of vegetation in areas uninvaded (control) and invaded by Chromolaena odorata Parameters Contol Invaded Percent increase over control Total species Margalef sindex Richness Menchinick s Index Richness Shannon Wiener s Diversity Index Simpsom s Diversity Index Pileou Evenness Index

4 The higher values of species richness and diversity index in invaded areas shows that plant communities in invaded areas are heterogeneous in nature and have more number of species than in non-invaded areas. Presence of some species (Crotolariajuncea, Lantana camara, Melastomamalabathricum and Philantusniruri) which only found in invaded areas certainly contributed to the high richness and diversity in invaded areas. Enhanced growth of these plants under invaded areas may be attributed to two factor. First, these plants are C3 photosynthetic pathway plants that fairly resistant to lower light intensity and temperature found under Chromolaena stand. This was in agreement with Whiteman (1980) that C3 plants need a lower light intensity and temperature to photosynthesis optimally than C4 plants. Second, those plants were apparently avoided by livestock because of their low palatability or thorny so they can escape herbivory. Those plants that escape the stress of grazing are may not weakened and their competitive ability to grow and reproduce is increased. This was in agree with Hjaltenet al (1993) that grazing onpalatable and unpalatable plants may reduced risk of herbivory of unpalatable plants. Further, escaping from livestock trampling during grazing may be an additional factor that increased diversity of vegetation in invaded area as livertock generally graze among Chromolaena and rarely graze under this plant stand. In conclusion, the invasion of Chromolaena in overgrazed did not harm overgrazed pasture ecosystem and even, it improves ecosystem functioning by increasing number of species,richness, biodiversity and evenness index, although it may reduces grazing area and availability of forage. It needs further study to determine floristic composition in depth and soil fertility in invaded areas and uninvaded areas. REFERENCES Callaway, R. M., Z. Kikvidze and D. Kikodze Oikos, 89: Goodal, J. M., and P. J. K. Zacharias Managing Chromolaenaodorata in subtropical grasslands in Kwazulu-Natal, South Africa. Proc.5 th Int. Workshop on Biological Control and managementof Chromolaenaodorata, Durban, South Africa, October Hjalten, J. K. Danell and P. Lundberg Herbivore avoidance by association vole and hare utilizationof woody plants. Oikos, 68 : Isbell, I. and Wilsey, B. J Effects of exotic species and overgrazing on biodiversity and ecosystem functioning.of The 94th ESA Annual Meeting (August , 2009). Albuquerque Convention Centre, Albuquerque, New Mexico. Margalef, R Temporal succession and spatial heterogeneity in phytoplankton.in : Perspectives in Marine Biology,Buzzati Traverso (ed.), Univ. Calif. Press, Berkeley, pp Menchinick, E. F A comparison of some species individuals diversity indices applied to samples of field insects. Ecology, 45 (4) : Metera, E. and T. Sakowski, Grazing as a tool to maintain biodiversity of grassland a review. Animal Science Papers and Reports vol 28.no. 4, Institute of Genetics and Animal Breeding, Jastrzębiec, Poland. 143

5 Nolubabalo,T Long-term impact of Chromolaenaodorata (L.) invasion and ungulate grazing on ant body size and communities in Hluhluwe-iMfoloziPark,South Africa. [ sun.ac.za/cib/handle/ /1178.] Pielou, E. C The measurement of diversity in different types of biological collections. Theoret. Biol. 13 : Shannon, C. E. and W. Wiener, The mathematical theory of communication. Urbana Unversity of Illionis Press,177 p. Tilman, D., P. B. Reich, J. Knops, D. Wedin, T. Mielke and C. Lehman, Diversity andproductivity in a long-term grassland experiment. Science, 294 : Whiteman, P. C Tropical Pasture Plants. Oxford University Press. 144