Managing Invasives: Narratives Of Scale

First published in Sanctuary Asia, Vol. 44 No. 2, February 2024

By Ramesh Venkataraman, R. Sundararaju and Pranav Capila

Invasive alien species are among the leading causes of ecosystem degradation, global biodiversity loss and species extinctions; their impact on native biodiversity has been recognised as “immense” and “insidious” (IUCN Guidelines for the Prevention of Biodiversity Loss Caused by Alien Invasive Species, 2000).

Invasions severely impair the ability of natural ecosystems to provide ecosystem services, as in the case of black wattle Acacia mearnsii, which impacts the water harvesting capacity of the Shola grassland ecosystems of the Western Ghats. A high presence of invasive species also reduces the availability of food for herbivores in the forests, resulting in greater ingress of wild fauna into human landscapes and increasing situations of conflict. Further, alien species reduce the ability of native ecosystems to mitigate or withstand the adverse impacts of climate change. Therefore, invasions are generally considered next only to deforestation in terms of adverse impact.

Bright colours, tubular flowers and ample nectar of the Lantana camara are a big draw for insects such as the striped tiger butterfly. However, lantana is the most widespread coloniser across India’s Protected Areas, crowding out native species and leading to biodiversity loss. Photo: Arushi Kanwar/Sanctuary Photolibrary.

A recent study published in the Journal of Applied Ecology (JAE) has provided the first-ever account of the distribution of high-concern invasive plants at a national scale in India. Fieldwork for the study was conducted as part of the quadrennial all-India tiger population assessment in 2018, so a large part of the country’s natural areas, about 358,550 sq. km., could be sampled. The study recorded the presence of one or more among 11 high-concern invasives – including Lantana camara, Prosopis juliflora, Senna tora and Chromolaena odorata – across 72 per cent of the sampled area (about 254,880 sq. km.). Significantly, it posited through modelling that over two-thirds of India’s natural areas (66 per cent or about 750,905 sq. km.) are potentially threatened by these invasive species.

Managing invasives, particularly at large scales, is resource-intensive and needs long-term efforts. A 2009 report estimated that the cost of removing lantana (the most widespread coloniser in India’s Protected Areas) ranged from Rs. 6,000-9,000 per hectare (current estimates would be much higher with inflation and increase in invasion densities), using the most economical and effective Cut Root Stock (CRS) method followed by subsequent ecological restoration activities – since removal is never an end in itself. The JAE study extrapolated from this report to estimate that “the least cost [for managing all high-concern invasives] with the present expanse of invasions would exceed […] Rs. 1.1 trillion,” with additional costs for managing reinvasions.

While these numbers appear daunting, experts believe that it is possible to adopt a strategic and co-ordinated approach and restore high-priority invaded areas so that biodiversity and ecosystem service benefits are maximised over 15 to 20 years. The scale of invasion may be high at a national level and lead to a sense of despondency, but when seen at the level of an individual forest range or panchayat, it can be manageable. What is important is that various stakeholders need to come together: NGOs and local communities working in closer cooperation with Forest Departments, but also with each other, so that individual projects in a particular geographical area can synergise and achieve greater cumulative scale.

Although removing invasives is an urgent need, it requires a scientific and cautious approach. High movement of people, vehicles and materials inside forest areas for the removal of lantana, for instance, can lead to collateral damage to indigenous species and risk the spread of other invasives such as Senna spectabilis. Photo: Public Domain/Mauro Halpern.

The Financing Question

There is considerable discussion on how the task of managing invasive species can be funded, given the high amounts involved. One view is that scale is best achieved through commercialisation – which means demand must be created for the harvested biomass of invasive plants and the revenues generated from there used for further removal.

In India, taking lantana as an example, such initiatives have thus far largely taken the form of small cottage-industry projects wherein artisanal products made from lantana wood, such as furniture and artefacts, are marketed. The idea is that some of the invasive plants are removed in this process and, simultaneously, a new livelihood source is fostered for forest-dependent communities that make these products. These products also play a role as ‘statement pieces’ that draw wider attention to the problem of invasives.

Proponents of commercialisation have suggested that rather than focusing on artisanal products, large-scale economic use should be the way forward: industries that could use the biomass of invasive plants could be tapped into; invasive species could be harvested in large quantities by local communities and the biomass converted into products such as fuel briquettes, or used as wood-substitutes for paper making, and so on. However, the implications of creating high commercial value for invasive weeds needs careful assessment from an environmental perspective, especially when planned to be carried out at large scale by multiple agencies other than the forest department.

Interventions that attach a high value to invasive alien species and make local communities dependent on them can be inherently counterproductive, leading to preservation and propagation rather than eradication. A cautionary tale lies in the Banni grasslands of Kutchh, where Prosopis juliflora has invaded large parts of the grasslands historically used by local pastoral communities for livestock grazing. These communities now derive a livelihood by converting the Prosopis into charcoal; its removal could impact them adversely and is hence not deemed desirable. This kind of trade-off between livelihoods and biodiversity could potentially repeat itself in other parts of the country.

Restoring one acre of lantana can generate employment of over 100 person-days over a four-year period. Restoration involves a number of activities other than removal, such as collecting seeds, reversing soil and hydrological degradation, introducing plant propagules, follow-up maintenance, etc. Importantly, almost three-fourths of these spends accrue directly to local community members. Photo Courtesy: Junglescapes.

Commercial exigencies may also be incompatible with the scientific principles of restoring weed-invaded areas. The removal process requires the adoption of scientific and species-specific methods aimed at minimising the possibility of re-emergence either from the same plant or from sub-soil seed banks. These methods conform to sound principles based on minimal collateral damage to native vegetation and avoidance of soil disturbance. Such principles and scientific methods are often time and resource intensive, and large-scale commercial harvesting may not always adhere to these.

The globally accepted principle in ecological restoration is to tackle invasives in areas, where they have a low to medium presence, i.e., where the invasion is new and not yet fully established (IUCN Guidelines, 2000). This is to avoid a full-blown invasion in the newly-invaded areas, to halt the invasion and prevent its spread to new areas, and to quickly restore native biodiversity over as large an area as possible, thus creating a nucleus of native propagules. On the contrary, commercial activities aimed at collecting the maximum biomass within a short time may entail removal from heavily invaded areas, allowing fresh invasions in other locations to spread unattended. Also, heavily invaded areas tend to be taken over, post removal, by secondary invasives. Commerce-oriented removal is also likely to target mature plants that provide greater biomass in preference over juveniles and seedlings, leading to re-invasions by the latter in a short period of time. For example, a paper mill harvesting an invasive tree species for wood pulp may prefer adult trees over juveniles and seedlings, leading to re-invasions in a short period. In other situations, the entire plant may not be removed and only branches of a certain size and thickness harvested; such plants then grow back rapidly.

The removal of invasives on a large scale also requires significant movement of people, vehicles and materials inside forest areas, which has two major impacts: one is the collateral damage on indigenous species; the second is the high risk of spread of other invasives such as Senna spectabilis and Chromolaena odorata, which are dispersed by the tyres and undercarriage of vehicles. Most forest areas with linear intrusions witness a heavier incidence of secondary invasion.

Other concerns remain. Commercial goals may take the focus away from long-term ecological restoration activities (given that removal is only a portion of the larger task). Products such as briquettes may result in a significant release of captured carbon into the atmosphere. Importantly, though commercial initiatives based on invasives have been attempted around the world, adequate scientific evidence is yet to emerge on whether these have met the goals of biodiversity restoration in a sustainable manner.

The globally accepted principle in ecological restoration is to tackle invasives in areas where they have a low to medium presence, i.e., where the invasion is new and not yet fully established (IUCN Guidelines, 2000). Photo Courtesy: Junglescapes.

Solutions From Within

The arguments offered in favour of large-scale commercialisation are that it can help generate the impetus and the revenue required for removal of invasive species, and provide livelihoods for local communities. There is also a question as to how one deals with the biomass generated by removing invasives. There is an alternate narrative that offers solutions to these issues from within the ambit of ecological restoration.

A sustainable way of raising funds for restoration would be through the carbon credit mechanism. It is well established, after all, that biologically and structurally diverse ecosystems sequester more carbon than invaded forests, which are closer to monocultures. In the Indian context, there has been interesting work done by the Indian Institute of Science on the carbon sequestration potential of structurally different forest types. Carbon credits could be a game changer for restoring invaded grasslands in particular, since recent research shows that these ecosystems could be more reliable at carbon sequestration than forests.

There is also an increasing global focus on the need to revive biodiversity, as a result of which newer mechanisms such as biobanking offsets are emerging. These may provide attractive sources of funding. International agencies are already funding biodiversity restoration activities more actively –it has just been announced, for instance, that the World Bank is funding a Rs. 2,000 crore project for the preservation and restoration of targeted coastal ecosystems in Tamil Nadu.

Native to the Americas, Chromolaena odorata has been introduced to tropical Asia, West Africa and parts of Australia. Commonly known as Siam weed, it is one of 11 high-concern invasives that could potentially threaten over 66 per cent of India’s natural areas. Photo: Public Domain/Vengolis.

Regarding the issue of the removed biomass, which is secondary to the challenges of raising funds and post-removal restoration, options exist for using the same effectively as part of restoration. For example, bio char made from these can be utilised for improving soil quality and moisture retention in restoration plots, since carbon returned to the soil in this way remains locked in for very long periods of time. Removed invasives can also be used as bio-fences to protect the native saplings being planted from herbivory. Invasive tree species that are removed can be used to create small biomass check dams to improve water tables, or as barriers to prevent soil erosion. There is good scope for maximising the use of  removed plants for ecological benefits, with residual biomass used by local communities for small-scale craft activities or as fuelwood (reducing the need to access native plants for fuelwood).

Finally, it should also be recognised that restoration is human resource intensive. For example, restoring one acre of lantana can generate employment of over 100 person-days over a four-year period. Importantly, almost three-fourths of these spends accrue directly to the local community members. Extrapolated to a national scale, this can help create a very significant restoration-based rural economic model, while leveraging the traditional ecological knowledge of these communities. Restoration by itself may thus present a far greater, but as yet untapped, opportunity to achieve multiple objectives of fund raising, livelihood generation and biodiversity revival.

(With inputs from Dr. K. Anand, alumni of Indian Institute of Science, Bengaluru)

Ramesh Venkataraman is a Certified Ecological Restoration Practitioner working on large-scale restoration of areas invaded by Invasive Alien Species. He is a member of the Task Force on Best Practices of the UN Decade on Ecosystem Restoration. R. Sundararaju, IFS (Retd.) was Principal Chief Conservator of Forests and Chief Wildlife Warden, Tamil Nadu Forest Department and has extensive experience on managing different Invasive Alien Species. Their views expressed here are personal. Pranav Capila is an independent writer and editor.


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