Protected areas (PAs) across India today are invaded by alien invasive species that include Lantana camara, Mikania micrantha, Chromolaenaodorata, Ageratumconyzoides, Parthenium hysterophorus, and Hyptis suaveolens. Although difficult, restoring landscapes colonized by invasive species is important for the conservation of biodiversity and for the sustenance of other ecosystem services.
Lantana (Lantana camara), one of the world’s most troublesome weeds, has virtually invaded all the tropical and subtropical regions of India. Although attempts have been made to control lantana by physical, chemical and biological methods, there has been little success either in its control or in the prevention of its spread. The control methods in use at present remain inadequate and infeasible owing to the sheer magnitude of the infestations, low land values, and lack of incentives for control. The lack of understanding of the species’ biology and lack of site-specific information of its ecology are major bottlenecks in developing effective tools for its management. It has yet to be recognised, for instance, that habitat degradation has triggered the invasion of lantana and that a final solution has to come in the form of habitat restoration. The methods that have been in practice for controlling lantana typically included chopping the main stem at the base, clipping aerial shoots and burning the clumps, and uprooting. Although these methods do bring about a short term reduction in the cover of lantana, with the onset of monsoons, profuse coppicing from multiple growing points occurs. Clipping is totally ineffective and only causes the clumps to spread and become harder. Burning results in coppicing from the buried meristematic zone and also increases soil erosion. Burning on a large scale is normally not resorted to in PAs, besides the fact that this practice may actually be advantageous to the weed in the long run. Uprooting, besides being labor intensive, disturbs the soil, exposes the buried seeds of lantana, and leads to their rapid germination.
Building on past experience with lantana management, and on the basis of a systematic assessment of its biology (the magnitude of its spread, its phenology, the distribution of growth points from which the plant re-sprouts or coppices, its architecture-including root system-soil microbiology and seed dispersal strategies) we ventured to develop a new management strategy, the ‘cut rootstock method’. This method involves the of lantana by cutting below the rootstock (see photograph), which we determined, experimentally, to be the most effective way of preventing it from coppicing. This is followed by ecological restoration using locally available legumes and grasses. Landscapes where lantana has been removed using this method need to be re-weeded, especially under trees where the bird dispersers of lantana perch. lantana removal must be followed by restoration of weed-free landscapes, preferably of grassland or forest communities depending on the needs of stakeholders, to prevent reinvasion by lantana or secondary invasion by other alien species. The new strategy was developed using experimental plots at Laldhang and Jhirna at Corbett Tiger Reserve and has subsequently been implemented successfully in other parts of Corbett (Uttara-khand), Kalesar National Park (Haryana) and Satpura Tiger Reserve (Madhya Pradesh).
The two experimental plots at Corbett have been the flagships of this control strategy that involved effective removal and ecological restoration of ‘weed-free landscapes’. The plots were browsed by chital and there was some mortality, but it was not a serious impediment because herbivore numbers were small, since this area had been a settlement till quite recently. We were able to achieve high survival rates (measured on an annual basis) for tree saplings because of modi!cation of soil conditions and the habitat by short grasses such as Penisetum ciliaris, Eulaliopsis binata, Heteropogon contortus, Paspalidium scrobicularis, Cynodon dactylon, and Sporobolus indicus, as well as leguminous species like Desmodium gangeticum, D. tri!o-rum, Flemingia bracteata, F. fruticosa, F. macrophylla, Indigof-era astragalina, and I. hirsuta). The experimental plots are now fully covered with a carpet of several grass species and legumes, with scattered trees.
At Laldhang, the Corbett management has scaled up the restoration plot to 64 ha. The area was fenced off due to frequent instances of cattle grazing from nearby villages. This plot now harbours luxuriant grassland with few interspersed trees and diverse avifauna. The Jhirna plot was left unfenced because there was no cattle grazing. This plot is now frequented by large herds of such browsers as chital and sambar, which form the major prey base for carnivores. So far there have been several recorded tiger sightings at Jhirna in the vicinity of the restoration plot (including carcasses of kills within the plots). The two plots established at Jhirna and Laldhang, using the integrated control and restoration strategy outlined above, are now used for demonstration of the technique. At both sites, the original relative density of lantana clumps varied from 80% to 100% and the areas were devoid of native species except for a few scattered trees that served as perches for bird dispersers of lantana. Within 2 years of the restoration program at Corbett (June 2005 to June 2007), both demonstration plots harbored grassland communities with annual and perennial native grasses and legumes. Several workshops and hands-on training programs were also held to enable foresters and park managers to scale up the lantana control and restoration measures, with field visits to the plots and demonstration of the technique employed. Various aspects of this model including the costs and benefits of clearing lantana and then converting the landscape into productive grasslands and woodlands, were highlighted to gain wider acceptance for the model. A simple manual was developed and widely circulated to aid foresters in removing lantana by the cut-rootstock method and to identify the grasses and legumes used in the Corbett model.
Subsequently, other forest managers of Uttarakhand State have adopted this technique. These forests include the Rajaji National Park, Landsdowne Forest Division, and Nainital Forest Division. In Corbett itself, lantana has been removed from over 2500 ha and restoration of these patches is in progress under the supervision of the park management. The advantages of the new management strategy over other control methods currently used are its cost-effectiveness, its simplicity, and ease of adoption and the successful control of lantana that the technique ensures, without the use of chemicals or exotic biological control agents, and with minimal disturbance of the soil. One of the major reasons for the popularity of the cut-rootstock method has been the fact that the restored patches do not require care after the first two years, since all the species used are native. Forest departments of other states, convinced by the effectiveness of the approach, have already removed lantana from several hundred hectares of forest land, particularly around Panchmarhi Biosphere Reserve in Madhya Pradesh and Kalesar National Park in Haryana.
However, as we have learned from our experience in Corbett, the ultimate success of such a program relies heavily on the conviction and motivation of stakeholders. Landscapes degraded by invasive species are often extensive, and even as weeds are eradicated from one area, propagule pressure and thus, reinvasion, can persist due to the continuing presence of weeds in other areas. A well-coordinated removal program followed by restoration at suitably large scales is necessary to tilt the scales in favor of native species. A strong determination by the park managers was crucial for the success of such a program.
The benefits of lantana eradication and subsequent restoration to grasslands in Corbett have been many: enhanced biological productivity, particularly in terms of palatable species of grasses and legumes; greater retention of soil moisture; prevention of soil erosion; enrichment of native biodiversity; the increased frequency of wildlife sightings; and enhanced recreational values, since Corbett is a favorite desti-nation for eco-tourists and ornithologists.
We anticipate that our observations on lantana management in Corbett and the success of the Corbett model will help in developing similar management strategies for other PAs that are presently overrun by lantana and also other weeds such as Mikania micrantha, Chromolaena odorata and Parthenium hysterophorus. However, any restoration program for these other invasive species would also need to be informed by an understanding of the biology of the invader, the local soil and micro climatic conditions, the status of the ecosystem, the larger landscape matrix, and most importantly, the requirements of the stakeholders.
Suresh Babu is a Research Scientist with the Centre of Excellence Program, Center for Environmental Management of Degraded Ecosystems, University of Delhi, India.
Cherukuri Raghavendra Babu is Emeritus Professor at the Centre of Excellence Program, Center for Environmental Management of Degraded Ecosystems, University of Delhi, India.