A recent study has pointed out that invasive species taking over urban areas resulted in a total cost of $326.7 billion, at the very least, in the past five and half decades. The study, highlighted by a Mongabay-India (MI) article, states that India ranks second in the global list of countries ranked by the economic impacts of biological invasions.

Another 2022 study, quoted by the MI article, reports that India has suffered $127 billion worth of damages due to the cost of managing invasive alien species in the last six decades, averaging $2-3 billion annually. However, there is no data specifically looking at urban areas.

The study published in Science of the Total Environment, and highlighted by the MI report, finds that 61 invasive species led to a cumulative cost of $326.7 billion in urban areas between 1965 and 2021 globally, with an average annual cost of $5.7 billion. The study adds that these costs are “likely underestimated” as only 24 countries have reported losses, and there are no estimates available from 73 additional countries, including India, which have invasive species. The study says these results highlight the conservative nature of the estimates and impacts and emphasizes the urgent need for more focused assessments of invasive species’ economic impacts in urban areas.

The study finds that insects were responsible for more than 99% of reported costs, an estimated $324.4 billion, followed by birds causing losses worth $1.4 billion and plants causing losses worth $494 million, as reported in the MI article. The reported costs were highly uneven, with the sum of the five costliest species representing 80% of reported costs, according to the study. Most – 77.3% – of these costs were damage-related, principally impacting ‘public and social welfare,’ and were almost entirely in terrestrial environments.

The study adds that the ‘public and social welfare’ category includes local infrastructures such as electric systems, quality of life such as income, recreational activities, and personal goods such as private properties and lands, and public services such as transport and water. Tourism, trade, conservation agencies, and forest services are also included, the study adds.

In its abstract, the study says that urbanization is an important driver of global change associated with a set of environmental modifications that affect the introduction and distribution of invasive non-native species (species with populations transported by humans beyond their natural biogeographic range that established and are spreading in their introduced range... [these are referred to] as invasive species). These species are recognized as a cause of large ecological and economic losses. Nevertheless, the economic impacts of these species in urban areas are still poorly understood.

Late last year, a Down to Earth (DTE) article had highlighted another study that said that more than half of India’s natural systems are threatened by invasive plant species. The DTE article points out that about 66% of the country’s natural systems are threatened with invasive species, according to the report published in the Journal of Applied Ecology. The study offered the first account indicating distribution status of high-concern invasive plants spread across the country. The findings are a result of a national-level survey conducted in India, which noted that 158,000 plots in 358,000 square kilometres of wild area are invaded by alien species.

As reported by DTE, the study sampling effectively covered 31% of savannas, 51% of dry deciduous forests, 40 per cent of moist deciduous forests, 29% of semi-evergreen forests, 44% of evergreen forests and 33% of moist grassland savannas, Savannas were reported to have the highest susceptibility (87%) to invasions, followed by moist grasslands and dry deciduous forests each at 72%.

The evergreen forests were found to be least suitable for invasive species at 42% susceptibility. However, the suitability of individual alien plants and its drivers varied for each species.  Scientists involved in the study have said, according to the DTE report, that human modifications, shifting soil moisture regime, historical propagation of invasive plants and altered cycles of natural disturbances are the main driving factors behind the invasions. The increasing work population densities and proportional increase of demand for food, infrastructure, energy and socio-ecological drivers further threaten to intensify and possibly escalate the accelerating invasion.