The Green Strangler

How a Mile-a-Minute Weed Is Choking Nepal's Chitwan National Park

80%

Buffer Zone Invasion

20cm/day

Growth Rate

20+

Affected Districts

Introduction

In the dappled light of Chitwan National Park's lush forests, a silent crisis unfolds. What appears to be an ordinary green vine is steadily spreading across one of Nepal's most biodiverse landscapes, smothering everything in its path.

Fast Facts
  • Growth Rate: Up to 20cm per day 5
  • Local Name: Banmara ("Forest killer")
  • Buffer Zone Invasion: Up to 80% 7
  • First Appearance: 1963 in Eastern Nepal 7
Chitwan National Park landscape

Chitwan National Park - A UNESCO World Heritage Site under threat from invasive species.

The Silent Invasion: History and Spread

1963: First Appearance

Mikania micrantha first appeared in eastern Nepal 7

1992: Chitwan Invasion Begins

Flooding of Rapti River likely carried seeds into Chitwan National Park

Present: Widespread Colonization

Now spread across more than 20 districts in Nepal's Terai region 7

Local Names and Meanings
Local Name Language/Region Meaning
Banmara Nepali "Forest killer" - reflects destructive ability
Banlude jhar Local dialect "Forest covering plant" - describes smothering
Barahmase Local dialect "Twelve-month" - year-round growth
Growth Forms

Mikania exhibits two adaptive growth strategies:

  • Prostrate form: Carpets open areas
  • Climbing form: Scrambles up trees in forests 5

The Anatomy of an Invader: Physiological Advantages

Rapid Growth

Up to 20 centimeters per day under ideal conditions 5

Dual Reproduction

Both sexual (seeds) and vegetative (stem fragments) reproduction 5 8

Chemical Warfare

Produces allelopathic compounds that inhibit competitors 9

Reproduction Strategies
Sexual Reproduction

Up to 170,000 seeds per square meter with wind-dispersal capabilities 8

Vegetative Reproduction

Adventitious roots form at stem nodes; small fragments can establish new plants 5 8

Microbial Manipulation

Stimulates increases in:

  • Nitrogen-fixing bacteria
  • Ammonifying bacteria 4

This enhances soil nutrient availability, particularly nitrogen, creating a self-reinforcing cycle 4

Ecological Impacts: A Biodiversity Crisis

Native Flora Impact

Forms dense mats up to 1.5 meters thick that cover shrubs, herbs, and seedlings 5

Reduction in native species richness can reach 30% in heavily invaded areas 5

Threatened Wildlife
  • One-horned rhinoceros (habitat loss) 5
  • Pygmy hog (critical habitat degradation)
  • Bengal florican (grassland transformation)
  • Increased human-wildlife conflict 5
Ecosystem Impact Assessment
Soil Microbial Communities

Increases nitrogen-fixing and ammonifying bacteria 4

Soil Chemistry

Changes pH and organic matter content 5

Forest Structure

Creates dense, impassable thickets

Soil Fauna

Affects nematode feeding on bacteria 5

A Ray of Hope: Sweet Potato as an Ecological Weapon

Experimental Design

Two-year study using "de Wit replacement series" design with six different planting ratios of sweet potato and Mikania micrantha 8

Constant total planting density while varying species proportions

Tracked reproductive characteristics, pollinator visits, and seed viability 8

Sweet potato plant

Sweet potato (Ipomoea batatas) - A promising biological control agent against Mikania invasion.

Sweet Potato Impact on Mikania Reproduction
Reproductive Parameter Impact of Competition Significance
Flowering phenology Delayed budding and flowering 8 Reduces competitive advantage
Pollinator visits Decreased visits by bees and flies 8 Limits sexual reproduction
Seed production Reduced number, biomass, and germination 8 Lowers population expansion
Reproductive allocation Significantly reduced energy investment 8 Impacts long-term viability

The Scientist's Toolkit: Researching and Managing Invasion

Molecular Approaches
  • Transcriptome sequencing for gene expression analysis 1
  • RNA interference for targeted bioherbicides 3
  • ELISA for quantifying plant hormones 1
Remote Sensing
  • Spectral Mixture Analysis with Landsat imagery 2
  • Spatial distribution mapping
  • Invasion hotspot identification
Innovative Approach

Recent research has explored RNAi-based herbicides that can silence genes for chlorophyll-binding proteins, causing leaves to yellow and wilt 3 . This offers species-specific control without broad environmental contamination.

Conclusion: A Collective Battle for Nepal's Natural Heritage

The invasion of Mikania micrantha in Chitwan National Park represents more than just an ecological nuisance—it is a fundamental threat to biodiversity, local livelihoods, and the ecological services that support both.

The vine's combination of rapid growth, flexible reproduction, chemical weapons, and microbial manipulation make it a formidable opponent, one that has successfully colonized vast areas of one of Nepal's most protected landscapes.

Promising Solutions
  • Sweet potato competition shows ecological control potential
  • RNA interference offers targeted approaches
  • Improved monitoring with remote sensing
Global Implications

The battle against Mikania micrantha illustrates both the devastating impacts of invasive species and the innovative solutions that can emerge when we work with ecological principles.

References