Invasive species may be the wrong enemy on a changing subcontinent

Across India, campaigns against invasive alien species (IAS) are gathering administrative and judicial strength. Authorities now identify, map, classify and remove species considered ecological threats.

In the past year alone, India’s English-language press has produced consistent coverage of studies of ecological losses, state eradication actions, and human-wildlife conflicts related to such species. What was once a specialized scientific concern has become a visible public issue and priority.

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A recent court order in Tamil Nadu even portrayed Prosopis juliflora bushes as a near-statewide threat. Government records reported its clearance from 517 villages in 32 districts, while academic literature recorded the species throughout the state. The plants Lantana camara and Senna spectabilis face similar campaigns elsewhere in India.

The prevailing assumption is simple: remove invasive species and ecological recovery will follow.

But before we accept this, we must first ask: what was the state of the landscape before the spread of these species, and what conditions sustain them now?

Three patterns emerge from the evidence.

Physical changes usually came first

Across India, native ecological communities had already been transformed before invasive plants became dominant.

Colonial forestry, plantation expansion and settlement removed large areas of forest cover. Millions of hectares have been converted into tea, coffee, rubber, teak and eucalyptus plantations. Diverse habitats have given way to a simplified commercial landscape with lasting effects on soil biology, shade regimes and water cycles. Logging, roads, mining, firefighting, and chemical agriculture further fragmented habitats.

In places like Wayanad, forest edges were already degraded before species like L. camara spread into them. Biodiversity and its supporting conditions have already been decimated.

The removal of a species alone cannot restore what was before. Without functioning ecological relationships, a larger clearing creates new vacancies, often the very conditions into which another or the same invasive species can quickly return.

P. juliflora was introduced to India in 1877 as part of a misguided ecological experiment. Initially spread from the air, it spread to the guts of cattle that browsed the pods. Then came the “Green Revolution” and wider post-independence agricultural intensification. Channels have expanded. Wells proliferated. Fertilizer consumption has skyrocketed.

As a result, waterlogging and seepage increased in some regions, aquifers were depleted in others, and productivity began to decline on abandoned land. P. juliflora is a deep-rooted phreatophyte that can use such altered water and soil regimes. In parts of Tamil Nadu, scientists have linked its increase to irrigation-related moisture.

In other words, the plant was present for decades – what changed was the landscape around it.

Ecological disturbance

Climate change, nutrient loading, land use changes, freshwater disruption, biodiversity loss and chemical pollution are reshaping ecosystems around the world. These are largely the consequences of a globalized industrial culture that pushes for rapid urbanization and infrastructure expansion.

In three decades, India’s urban governance footprint has roughly doubled, marking a systemic expansion of fragmented, highly disturbed landscapes that extend far beyond city limits into peri-urban and rural ecologies.

India also supports roughly 500 million head of cattle and other livestock—one of the largest such populations in the world—putting constant and heavy grazing pressure on forests and communities. Under such conditions, “palatable” species are repeatedly suppressed, while thorny, chemically protected, disturbance-resistant plants such as L. camara persist or even expand.

Studies have revealed increasing forest cover in many open landscapes around the world, linked in part to rising atmospheric carbon and other interacting factors. Fertilizer inputs remain high—India alone uses 35–40 million tons of urea per year—and atmospheric nitrogen deposition now adds 10–30 kg per hectare per year in many regions. Nitrogen-fixing woody species such as S. spectabilis and P. juliflora benefit from these altered conditions.

A deeper invasion

Chemical pesticides further altered soils and microbial networks. Over time, they can disrupt genes, reduce resistance, amplify pest cycles, and weaken the ecological foundations upon which productivity itself depends.

These changes were driven not so much by individual choice, but rather by policies, infrastructure, and economic systems designed to maximize large-scale production. The result: food production must continue, but the same hydrological, chemical and atmospheric systems that increase production are also depleting the soil and degrading the ecosystems now to be restored.

When multiple factors change together, plant communities reorganize. The growth of P. juliflora is part of wider hydrological and chemical changes across the subcontinent. A similar dynamic may apply in different ways to other IASs. These plants can act as ecological first responders – species whose physiology is suited to rapid changes in landscape conditions.

Over time, these pioneer species are followed by other species. In the early stages, many can be exotic and fast moving. Eventually, even native species can re-establish themselves. However, such an ecological succession does not guarantee a return to earlier ecological states. As the underlying conditions continue to shift, new ecological associations are likely to emerge among the species that are able to thrive within them.

Life is conditional

Evolutionary and paleoecological evidence suggests that the world’s natural biomes evolved under very different climatic and nutrient regimes. Grasslands expanded during the drier phases of history, while rainforests emerged and diversified under warmer, wetter conditions. Many species cannot easily tolerate the nutrient-rich soils, altered climate, or hydrologically altered landscape of today.

Some IAS species may also fulfill compensatory ecological roles. They can accumulate heavy metals, nitrogen and carbon in biomass, provide shelter for smaller game in a disturbed landscape, create conditions into which other species later enter, provide windbreaks and bind the soil.

Of course, it has real consequences. Dense thickets of invasive plants can reduce available food for elephants and other herbivores in forests such as the Western Ghats. However, these effects occur in landscapes that have already been altered by logging, plantations and nutrient enrichment.

Conservation efforts that focus only on the visible plant thus risk misdiagnosing the problem. It is easier to count acres of IAS removed than to measure shifts in moisture regimes or soil chemistry. The removal alone does not fix the underlying drivers. Restoration requires us to read the land comprehensively, understand its history and interacting processes, and work with the ecological and human communities that remain.

What will it take

This does not mean that certain species should never be removed, but that recovery is difficult and requires attention to ecological processes and biodiversity. It is local, patient and continuous. Large mechanical removal brings complications in itself. While large-scale clearing may serve the emerging biomass economy, there is little evidence that it promotes ecological recovery, which takes time.

Fears of invasive species taking over often accompany business opportunities for farmers and new employment schemes. The villain seems to be able to revive the economy faster than recovery.

Communities and practitioners embedded in these habitats are often best placed to carry out careful removal where it makes ecological and cultural sense. However, success remains uncertain and can only be judged years later. Restoration should take place with as little damage as possible, gradual planting, intergenerational care and meaningful human livelihoods.

Otherwise, India risks devoting much of its conservation energy to removing plants that are symptomatic of a wider civilizational transformation it has yet to come to terms with.

Suprabha Seshan lives and works at Gurukula Botanical Sanctuary in Wayanad district, Kerala.