Introduction

The rolling hills and riverine wetlands of the Bodoland Territorial Region in Assam have long been celebrated for their extraordinary biodiversity. Among the most charismatic of its inhabitants are the butterflies, whose kaleidoscopic wings have become symbols of the state’s natural wealth. Yet, beneath the visual splendor lies a complex ecological puzzle: native flowering plants often fail to provide continuous nectar throughout the year, leaving pollinators vulnerable during seasonal gaps. Recent fieldwork in Raimona National Park has revealed an unexpected ally in this struggle—two invasive plant species, Lantana camara and Chromolaena odorata. While traditionally vilified for out‑competing indigenous flora, these species now appear to function as critical, year‑round nectar reservoirs for a broad assemblage of butterflies.

This article re‑examines the role of invasive flora from a conservation‑policy perspective, weaving together historical context, quantitative findings, and regional implications. By shifting the narrative from “enemy” to “potential partner,” we aim to equip policymakers, land‑managers, and community stakeholders with a nuanced framework for balancing ecosystem integrity with pollinator health across Northeast India.

Main Analysis

1. Historical Trajectory of Invasive Plants in Assam

Both Lantana camara and Chromolaena odorata were introduced to the Indian subcontinent during the British colonial era. Lantana, originally native to tropical America, entered Assam in the early 1900s as an ornamental hedge and later as a hedge for tea plantations. Chromolaena, a fast‑growing vine from Central America, was brought in the 1960s for soil‑erosion control on degraded slopes. Within a generation, each species had proliferated across disturbed habitats, riverbanks, and agricultural margins, earning the label “invasive” due to their aggressive colonisation and suppression of native understory plants.

Traditional management strategies have focused on eradication through mechanical removal, herbicide application, and community‑led “weed‑pull” campaigns. However, these approaches often overlook the secondary ecological services that invasive species may inadvertently provide, especially in landscapes where native flora is fragmented or seasonally dormant.

2. Quantitative Evidence from Raimona National Park

Between 2019 and 2022, a multidisciplinary team of entomologists, botanists, and local forest officers conducted systematic transect surveys across the 90‑km² expanse of Raimona National Park. The methodology combined line‑transect counts for adult butterflies with timed‑flower observations to record nectar‑feeding events. The key findings are summarised below:

• Total butterfly diversity recorded: 220 species, representing 12 families, including 45 endemic to the Eastern Himalayas.
• Host‑plant inventory: 56 plant species identified as larval hosts, of which 38 (68%) are native to the region.
• Nectar‑plant inventory: 41 flowering species observed providing nectar, with 23 (56%) classified as non‑native.
• Seasonal nectar gaps: Native flowering peaks in May‑July and September‑November, leaving a pronounced nectar deficit from December through March.
• Contribution of Lantana camara: Documented visits by 32 butterfly species (≈15% of the total assemblage) from April to October, coinciding with the dry season when many native shrubs are dormant.
• Contribution of Chromolaena odorata: Visited by 24 butterfly species (≈11% of the total) from December to February, effectively bridging the winter nectar void.
• Overall nectar coverage: When the two invasives are combined, they supply continuous nectar for 46 distinct butterfly species (≈21% of the park’s total) across all months of the year.

Statistical analysis using generalized linear models (GLMs) demonstrated a significant positive correlation (p < 0.01) between the abundance of invasive flowering stems and butterfly visitation rates, even after controlling for habitat type, temperature, and precipitation. This suggests that the relationship is not merely opportunistic but reflects a functional dependence on the invasive nectar source during periods of native scarcity.

3. Ecological Mechanisms Underpinning the Invasive‑Butterfly Interaction

Three primary mechanisms explain why these non‑native plants have become indispensable nectar providers:

1. Extended phenology: Both species flower almost year‑round. Lantana produces multiple flushes of small, tubular flowers every 30‑45 days, while Chromolaena blooms continuously in response to light availability, irrespective of seasonal temperature shifts.
2. High nectar volume and sugar concentration: Laboratory analyses of nectar from Lantana and Chromolaena reveal average sugar concentrations of 22 % and 19 % respectively—higher than most native understory herbs (typically 12‑15 %). This makes them energetically efficient for butterflies that require rapid fuel replenishment during migration or reproduction.
3. Habitat generalism: The invasives thrive in disturbed soils, roadside verges, and secondary forests, creating a mosaic of feeding stations that are accessible even to edge‑dwelling species that avoid deep forest interiors.

4. Regional Implications for Conservation Policy

Assam’s forest management policies have historically prioritized the removal of invasive flora to protect timber yields and preserve “pristine” ecosystems. However, the data from Raimona suggest that a blanket eradication strategy could inadvertently exacerbate pollinator declines, especially for species already threatened by habitat fragmentation, pesticide exposure, and climate‑induced phenological mismatches.

Three policy pathways emerge from this analysis:

• Adaptive Management: Instead of universal removal, managers could adopt a spatially explicit approach, retaining invasive patches in zones where native nectar plants are absent, while targeting removal in core conservation areas where endemic flora can be restored.
• Integrated Restoration: Planting native nectar species with overlapping flowering periods—such as Hedyotis sp. and Impatiens balsamina—can gradually replace the functional role of invasives, reducing reliance on non‑native plants over a 5‑10‑year horizon.
• Community‑Based Monitoring: Engaging local villages in citizen‑science programs to track butterfly abundance and flowering phenology can provide real‑time feedback on the ecological trade‑offs of invasive management, fostering co‑ownership of conservation outcomes.

5. Broader Ecological and Socio‑Economic Context

Butterflies serve as bio‑indicators of ecosystem health, pollinate a range of wild and cultivated plants, and support tourism—an increasingly important revenue stream for Assam’s rural economies. The state’s “Butterfly Trail” initiative, launched in 2021, attracted over 12,000 domestic tourists in its inaugural year, generating an estimated INR 4.5 crore (≈ USD 600,000) in local income. Maintaining robust butterfly populations, therefore, has direct socio