Clearing Off the Uninvited
By Ama H. Vanniarachchy
The Lunugamvehera National Park, declared in 1995, is home to a large number of mammals and aquatic birds. This park also serves as a corridor for elephants who migrate between Yala and Udawalawe National Parks. According to the Sri Lanka Wetlands Information and Database, the park includes 21 fish species, 12 amphibians, 33 reptiles, 183 birds, and 43 mammals. Among the mammals, elephants are notable residents and visitors of the park. The Federation of Environmental Organisations (FEO) notes that there is a rapid spread of invasive species at Lunugamvehera National Park that causes great threats to the existence of the wildlife at the park.
The spread of the many invasive species has resulted in creating food scarcity for herbivorous animals, which eventually affects the entire food chain and results in unbalancing the park ecosystem. This has also resulted in an increase in the human-elephant conflict (HEC). To know more about this, we contacted Chairperson of FEO Sri Lanka, Dr. Yohan Weerasuriya. “It is estimated that around 5 per cent of the land area at the Lunugamvehera National Park is currently taken over by invasive plants,” said Dr. Weerasuriya. “Among them, Lantana camara (Gandapana) and Eupatorium odoratum (Podi Singho Maran) are the most dominant as they are rapidly spreading across the park.”
They are a threat to the ecosystem
As Dr. Weerasuriya explained to us, the extensive spread of invasive plants inhibits the growth of native plant species and thereby causes extensive loss of habitat and grazing grounds in the park, posing a serious threat to the elephants and other herbivore populations that are resident or visit the park and their interconnected ecological food networks. “Poor land use management practices, together with water scarcity, has enabled many invasive alien plant species to establish and spread extensively within the national park,” he said. As he further explained, these invasive plants rapidly displace native vegetation with their capacity to grow, reproduce and disperse, tolerate harsh environmental conditions, and deter herbivores from consuming their required daily plant biomass.
“The problem is aggravated by the fact that Lantana camara is toxic to herbivores and thus, is not a suitable alternative fodder. Further, the Eupatorium odoratum plant will shade out the growth of grass while the thick growth of Lantana camara will block access to water bodies, shade, and escape cover.” A well-known negative impact of invasive alien species is the long-term irreversible changes to the biodiversity of the host ecosystem, in this case, Lunugamvehera and its surrounding habitat, central to the survival of much wildlife. “This altering of the ecological balance will cascade through food webs affecting the entire diversity within the park,” clarified Dr. Weerasuriya.
Impact on the HEC
However, as the FEO observes, this issue is most critical to the survival of elephants and large ungulate residents in and visiting the park. This leads to a graver issue. The loss of primary feeding grounds for elephants will lead to the escalation of the HEC as elephants look for alternative food sources. Lunugamvehera is linked to both the Yala and Udawalawe National Parks that enable frequent animal movements between these areas, as they seek food and water. The park is also surrounded by several villages, whose communities depend on agriculture for their livelihoods. “Lack of food often prompts animals to raid agricultural areas outside the park causing HEC. This is further escalated by incidents of poaching of wildlife which is widely recorded in the area,” Dr. Weerasuriya expressed his concern.
What FEO intends to do
To keep things under control, the invasive plants should be removed and then monitored. As the FEO explained, invasive plant removal has been previously attempted in the park using multiple methods (bulldozing, using brush cutters, manual removal, and burning). Most of these previous methods, other than manual removal, have also removed other plant populations, including the much-needed native plants and seed banks, further facilitating the spread of invasive plants. Dr. Weerasuriya explained to us that the dispersal of the focal invasives within the park, thereby, can be categorised into two major groups and several subcategories of age classes: (a) Old-growth (never removed), primarily within the vegetation (in clumps) and along the roadsides (b) Re-growth along with the previously cleared areas (less than 6 months old, 6 months to 1 year, 1 to 2 years, and over 2 years) The FEO conducted a study on the invasive plant spread at Lunugamvehera.
On 23 January 2021, the FEO carried out a site visit, with the Department of Wildlife Conservation (DWC), to assess the severity of the invasive plant growth within the park. Upon receiving the DWC approval to carry out the project, on 6 and 7 February 2021, the FEO carried out pilot tests to scientifically establish the cost and effectiveness of alternative methods of removal of the Lantana camara and Podi Singho Maran infestations. “The method of plant removal was tested at five different sites and the feasibility of alternative methods as well as practical issues of implementation were discussed at length with the Park Warden and other onsite DWC staff members,” explained Dr. Weerasuriya. Accordingly, the Project was initiated on 9 February 2021 along the main trails within the park.
These are thickly covered with a mixed growth of both species ranging from 2 -13 feet in height with an undergrowth of smaller younger plants. Rapid response in preventing seed dispersal is critical in controlling the spread of any invasive alien species. “Hence, urgent action is critical to remove these plants prior to seed generation, to facilitate the growth of native varieties,” emphasised Dr. Weerasuriya. A critical factor in the control of an invasive alien species (IAS) is early detection and rapid response in preventing seed dispersal.
Given that the life span of seeds of an invasive species can last up to several years sitting in the soil seed bank, totally eradicating an IAS within one growing season is not feasible. Hence, consistent maintenance of controls, for three to five years, is vital for the sustainable management of any invasive alien plant species. It is critical to remove IAS before the seeds mature and disperse. The attempt is to remove as much growth as possible manually (inclusive of roots), before they shed seeds. The remaining plants, which are more difficult to uproot, will be removed via a ‘slasher’ and the roots will be removed manually, at a later stage, when the soil is moist and plants may be easily uprooted.
The final disposal will undergo experimental trials (piling, piling and burning, piling and leaving to dry, and spreading and leaving to dry). Further, selected plots will be observed, on a weekly basis, to monitor the rate of regeneration of both the native and invasive plants. Dr. Weerasuriya enlightened us that the target for this year’s activity will be the clearing of over 80 per cent of the identified area and it is expected that this will minimise the spread of the plant during the successive years. “The process will have to be repeated for at least three to five years, to eradicate the focal plants from the cleared areas,” he said. “The costs for the recurring years will be less than the figure estimated for this year as there will be no ‘old’ growth, but plants of less than one year of age and those sprouting from the remnant roots. The seed bank would also be depleted as we will be removing a majority of the plants before seed dispersal.”
The Habitat Restoration Project
The total budget is estimated at Rs 49 million for clearing the IAS from approximately 900 hectares of the park (approximately Rs 50,000 per hectare). This Habitat Restoration Project is to be implemented by the FEO in partnership with the DWC.
A community-based project
The Lunugamvehera National Park is surrounded by communities whose livelihoods have been affected by the COVID-19 crisis. Therefore, this project intends to make a positive impact by providing them with a steady source of income by employing villagers for the manual removal of the invasive plants. Removal of the focal invasive plants will be by employing multiple crews, under the supervision and security of the DWC. The hired labour will be drawn from local communities who have lost their income sources due to the COVID-19 pandemic from local farming communities. Most of these people are registered at the park office as trained workers. In addition, those who are selected for the project will be given awareness training on invasive species control. “This community is being targeted with a view to establishing a community-based organisation that may, in the future, function as a supporting force for safeguarding the park and its surrounding environment,” concluded Dr. Weerasuriya.
Lantana camara (Gandapana)
It was introduced to Sri Lanka from South America in 1926, by the Royal Botanical Gardens, and was later popularised as an ornamental plant. Its invasive characteristics allowed the plant to infest diverse habitats and it is currently widespread in the Dry Zone of Sri Lanka. The plants can grow in clumps or as dense thickets, crowding out more desirable species. In disturbed native forests, it can become the dominant understory species, disrupting succession and thereby decreasing biodiversity. The spread of Lantana camara is aided by the fact that it produces thousands of berries every year, starting at a very early stage, that is fed on by a wide variety of birds and animals, and its seeds are then dispersed far and wide. In addition, its leaves are toxic to most animals and thus avoided by all herbivores.
Eupatorium odoratum (Podi Singho Maran)
A plant native to America, dispersed from the Royal Botanical Gardens in Peradeniya, in the 19th century. It’s a rapidly growing perennial herb that can grow up to 4 metres in height. It is one of the fastest spreading IAS plants in Sri Lanka producing up to 90,000 seeds per plant that are effectively dispersed by the wind. The seeds need light to germinate. It can also regenerate from the roots. It contains carcinogenic alkaloids which makes it toxic to herbivores.
The Federation of Environmental Organisations (FEO)
The FEO was founded by a group of concerned professionals and environmentalists in 2012 and is administered by a Board of Trustees. It is a non-political, non-partisan organisation that provides a platform for connecting interest groups with a patriotic interest in safeguarding Sri Lanka’s natural heritage through conservation and advocacy. It has a wide network of members, partners, scientists, professionals, Government officials, social media platforms, activists, and legal experts on whom to call on for partnering projects.