Ecology and conservation of the Grasslands of Eravikulam National Park, Western Ghats

Abstract

An ecological study on the montane grasslands of Eravikulam National Park (ENP), the Western Ghats, was conducted during 1992-1996, with the following objectives: (i). to prepare a complete floristic inventory of the grasslands of ENP, (ii). to identify the grassland communities, their structure, function and successional trends along the anthropogenic gradient, (iii). to determine the forage quantity in different ecological conditions and (iv). to study the effect of fire and tree plantations on the grasslands. : The ENP lies between 10° 5' to 10°20' N and 77° to 77°10' E with an area of 97 km? in the Southern Western Ghats. The average altitude of the plateau is 2000 m and the highest peak, Anamudi, reaches 2695 m. Soil was acidic with pH ranging from 4.6 to 4.8. The climate was dominated by monsoon. During the study period the annual rainfall ranged from 4697 to 5540 mm. Winter days (Nov- Jan) were cooler and frost was common. The two distinct physiognomic units of vegetation are grasslands and sholas, unique to the Western Ghats. 3: The study area was stratified into eight landscape units viz., slope without rocky outcrops, slope with rocky outcrops, flat top, valley, bog, shola-grassland edge, cattle grazed and scraped areas. Systematic surveys and vegetation parameters such as species association, frequency, diversity, evenness and richness were studied in each landscape unit by laying 5 m radius. 4. 308 plant species were collected from the grasslands, adding 106 new species to the earlier list. 51 species were found to be endemic to the grasslands and 29 were listed as rare and endangered species. There were 64 species common with Eastern Ghats, 30 species with Patanas of Sri Lanka, 35 with Western Himalaya and 35 with Naga and Khasi hills indicating phytogeographical affinities with different biogeographic zones. D! Vegetation association was derived using ‘TABLE TRANSFER METHOD’ and TWINSPAN (computer packages). TABLE TRANSFER method identified 23 vegetation associations and TWINSPAN identified 15 associations. In both the analyses it was found that Chrysopogon zeylanicus and Sehima nervosum were the two dominant species. The diversity index (H’) of the associations ranged from 1.38 in the Artemisia nilagirica-Heteropogon contortus-Cymbopogon flexuosus (cattle grazed area) to 2.90 in Agrostis peninsularis-Eulalia phaeothrix-Chrysopogon zeylanicus in the shola-grassland edges. Vegetation ordination i.e., Canonical Correspondance Analysis (CANOCO) indicated that clay, pH and sand were important environmental factors which determined the species distribution and abundance.6. Biomass study was conducted at three sites in three dominant communities viz., Chrysopogon zeylanicus, Sehima nervosum and Cymbopogon flexuosus. Clipping was done both inside the exclosure and outside to obtain net primary productivity (NPP). The NPP values showed that these grasslands are between tropical and temperate grasslands . Outside the exclosures NPP was maximum at Eravikulam and minimum at Lakkamkudi. But inside the exclosures all the three sites were having nearly equal amount of NPP. Above ground biomass (ANP) was maximum at Eravikulam inside the exclosures and less at Rajamala, where as below ground (BNP) biomass was more at Rajamala and less at Lakkamkudi. Rate of biomass production was more (3.1 g m day!) at Eravikulam inside the exclosure and less (0.8 gm? day!) at Lakkamkudi outside the exclosures. In all the communities monocots contributed more to the ANP (59-97 %) than dicots (3-41%). In Lakkamkudi Pteridium aquilinum (fern) contributed 10 % to the ANP. Sehima nervosum, Heteropogon contortus and Chrysopogon zeylanicus were the three dominant grass species according to ANP. The annual removal of ANP by cattle and wild ungulate from Lakkamkudi was 68 %. Z. Burning (early and late) was done in S. nervosum (Anamudi) and C. zeylanicus (Rajamala) community. It was found that both in the early and late burnt areas no significant changes were noticed on species diversity, richness and evenness. Regarding the structure of the vegetation, cover value of dicots showed significant difference between early and late burnt in different months. Both early and late burning affected the regeneration of Phlebophyllum kunthianum. 8. A comparison of various sites with different density and age of wattle plantations with unplanted area showed that the number of endemic species and food species of Nilgiri tahr decreased with increase in the age of plantation. The increase in weed abundance with the age of plantation indicated more harm to the natural vegetation. The diversity index (H’) was 2.64 in 10 year old plantation and 1.87 in 3 year old. TWINSPAN identified two plant species associations each in unplanted, 3 year old and five year old plantations, and four in 10 year old plantation. 9. The study recommends the following research and management strategies for the long term conservation of Shola-Grassland ecosystems and endangered Nilgiri tahr: (a) inclusion of adjecent reserved forests with shola-graslands in the park, (b) boundary verification and better patrolling to check the illegal activities and fire hazards, (c) early burning in selected areas on experimental basis, (d) control of black wattle spreading, (e) eco-development measures for the Lakkamkudi village, (f) better tourism management and (g) long term monitoring of exclosures and representative shola-grassland patches.