Plant Invasion in India: an Overview

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1 Plant Invasion in India: an Overview R.K. Kohlii, D.R. Batishi,J.S. Singh2, H.P. Singh3 and J.R. Bhatt4 1Department of Botany, Panjab University, Chandigarh, India; 2Department of Botany, Banaras Hindu University, Varanasi, India; 3Department of Environment Studies, Panjab University, Chandigarh, India; 4Director, Ministry of Environment and Forests, CGO Complex, Lodi Road, New Delhi, India Introduction The Earth's flora is dynamic and has been constantly changing over a period of time. Changes may be natural or human-aided, although in the recent past the latter has played a vital role. In fact, the movement of plants from one part of the earth to the other has become very common and frequent owing to better trade and transport facilities. Plant species that move from one geographical region to the other (either accidentally or intentionally), establish and proliferate there and threaten native ecosystems, habitats and species are known as invasive alien plants (hereafter referred to as invasive plants) (Richardson et al., 2000). The problem of invasive plants has become global and is largely human-aided (Vitousek et al., 1997). Invasive plants are responsible for global environmental changes, biodiversity crisis, species endangerment and disruption of ecosystem processes essential for human welfare (Drake et al., 1989; Parker et al., 1999; Mack et al., 2000; Mooney, 2005; Charles and Dukes, 2007; Herron et al., 2007, Pejchar and Mooney, 2009). The impact of invasive plants on global biodiversity is second only to habitat fragmentation and is a major global issue. Furthermore, the economic costs due to invasive species are also enormous, though not widely studied (Pimentel et al., 2005). Plant movement or introduction to an alien environment is not a new phenomenon but has been an important part of our history. A number of economically important plants such as crops and ornamentals are introduced plants that have proved especially beneficial and non-harmful to the human race. However, many introduced plant species initially considered to be valuable have become a nuisance and difficult to manage. Example include Lantana camara, a n shrub now known to be a very troublesome invader but now introduced to several parts of the world as an ornamental. There are also examples of accidental entry of some invasive plants as contaminants of imported food grains or agricultural/horticultural material or in ships' ballast water. An invasive plant such as Parthenium hysterophorus - one of the most serious invasive plants - is an example of accidental entry. Environmental problems such as climate change, disturbances and changing landscape patterns have further escalated the process of biotic invasion. The harms caused by biotic invasions are enormous as they interfere with the socio-economic system, human and animal health and food security of the region. Various international and national organizations, such as World Conservation Union (WCU, formerly IUCN - International Union for Conservation of Nature and Natural Resources), Convention on Biological Diversity (CBD) and Global CAB International Invasive Alien Plants: An Ecological Appraisal for the Indian Subcontinent (eds J.R. Bhatt et al.) 1

2 2 R.K. Koh li et al. Invasive Species Programme (GISP), are concerned with the prevention and control of this global problem. Status and Vulnerability of the Indian Region to Plant Invasion The Indian region, because of its diverse climatic and environmental conditions, is highly vulnerable to biotic invasion. Moreover, a burgeoning population, high rate of trade and transport, coupled with greater movement of people favour the accidental and intentional entry of plant species in this region. The recent fast rate of economic growth of the country is also expected to leave its mark on loss of plant diversity and increased invasion of alien species. Three hot spots of biodiversity, although supporting rich floral and faunal diversity including endemic species, also reflect a high rate of habitat degaradation where opportunist invasive species can easily establish themselves. Consequently, a numer of invasive species have made their abode in the region. The three main reasons for the greater invasibility of this region could be listed as follows: excessive human populations that migrate frequently and carry seeds or propagules of invasive plants from one place to another; availability of fragmented/disturbed habitats or species-poor regions due to habitat fragmentation and degradation that provide habitat for alien species; and favourable environmental and climatic conditions owing to the diversity of seasons and climatic variations that give invasive species an opportunity to establish. Invasive plants such as Ageratum conyzoides, Eupatorium adenophorum, Eupatorium odoratum, Lantana camara, Mikania micrantha and Parthenium hysterophorus have caused havoc in terrestrial ecosystems, and Eichhornia crassipes, Ipomoea spp. and Salvinia molesta in aquatic ecosystems (Raghubanshi et al., 2005). Despite several known invasive plants in India, there is no complete listing of the status of invasive plants. According to one source, around 18% of Indian flora are adventive aliens, of which 55% are from, 30% from Asia and 15% from and Central Asia (Nayar, 1977). More recently, Reddy (2008) has identified 173 invasive plants belonging to 117 genera and 44 families, based on his comprehensive work. (74%) and tropical Africa (11%) have contributed most to the invasive flora of the country. Besides, there are several other reports available that provide information on the invasive flora of a particular region/area. For example, Kohli et al. (2004, 2006) have provided information on the status of invasive plants in the north-western Himalayan region and have stated that three invasive weeds - Ageratum conyzoides, Parthenium hysterophorus and Lantana camara - found in this region have caused considerable harm to the fragile biodiversity. Several reasons, such as fragile soil, anthropogenic activity, tourism, pollution, rapid industrialization/ urbanization and the livestock-dependent lifestyle of the aboriginals such as the Gaddi or Gujjar communities, are responsible for the establishment of invasives and declining biodiversity (Kohli et al., 2009). Khuroo et al. (2007) reported 571 alien species belonging to 352 genera and 104 families from the Kashmir Himalayas, their origins traceable from, Asia and Africa. Negi and Hajra (2007) reported 308 woody and 128 herbaceous exotic species from the Doon Valley of the north-western Himalayas of which many are harmul invasives that have created several environmental, socioeconomic and health problems. Major Invasive Plants and their Attributes Based on the available databases and some regional reports, nearly 60 invasive plants have been identified from the Indian region (Table 1.1), the majority from South and tropical and Australia, Africa,

3 Plant Invasion in India 3 and even the Asian region. Table 1.1 includes Arundo donax - a grass of Indian origin that can pose a major threat to biodiversity owing to its capacity to invade huge areas around water bodies. Most of the invasive plants, irrespective of their origin, belong to the family Asteraceae, while families such as Poaceae, Solanaceae and Fabaceae also predominate. Furthermore, invasive plants belong to a variety of life forms such as herbs, shrubs, trees, climbers/ vines, grasses and aquatic plants (Table 1.1). Important invasive plants that have created havoc in a number of habitats include terrestrial herbaceous weeds (e.g. Ageratum conyzoides and Parthenium hysterophorus), shrubs (e.g. Lantana camara and Chromolaena odorata), trees (e.g. Prosopis juliflora and Leucaena leucocephala), vines (e.g. Mikania micarantha) and aquatic plants (e.g. Eichhornia crassipes). These have entered the alien environment by one of two main pathways - either intentionally to serve some human purpose or accidentally (through import of agricultural/horticultural material, human beings, ballast water, etc.). Lantana camara is perhaps the bestknown example of a serious weed having been intentionally introduced for ornamental value, in this case from tropical to other parts of the world. Lantana camara is now rated as one of the worst invasive species identified by the Global Invasive Species Database and is also included in the top 100 invasive species of the world (GISD, 2010). In India, it was introduced at the beginning of 19th century as an ornamental plant, and is now found widespread in almost the whole of the subcontinent and has encroached even at high altitudes (> 1700 m) in the Himalayas (Koh li et al., 2006). Lantana is a serious invader of forests, grasslands, agricultural land and vacant urban areas, and also in protected areas, and this has implications for the vegetation structure and dynamics (Koh li et al., 2004; Sharma and Raghubanshi, 2007; Sahu and Singh, 2008; Love et al., 2009). Another weed introduced in India as an ornamental plant is Chromolaena odorata (National Focal Point for APFISN, 2005), and this is also included in the list of the top 100 worst invaders (GISD, 2010). It is also one of the most obnoxious weeds in the Western Ghats, north-eastern parts of the country and impacts on coconut, rubber, coffee and teak plantations (Singh, 1998). Mikania micrantha (Asterceae), commonly known as mile-a-minute, was introduced for camouflaging airfields during the Second World War (Randerson, 2003). It is now a very noxious weed in plantations and forests, especially in the southern and north-western parts of the country (Muniappan and Viraktamath, 1993). s such as Leucaena leucocephala and Prosopis juliflora introduced under various forestry programmes are also now of invasive proportions. Of species introduced accidentally to the region, Parthenium hysterophorus is one of the most harmful weeds and the best-known example (Koh li and Rani, 1994). It grows rapidly in vacant areas, agricultural land, pastures, urban areas and natural and manmade forests, where it forms its own monoculture stands. It is found in every state and union territory of India except at higher altitudes and has now covered nearly 2,025,000 ha of land (Aneja et al., 1991). It spreads mainly through its minute seeds, which are blown easily by wind and water. Likewise, Ageratum conyzoides is a fastspreading weed, is the most serious invader of agricultural land and is a problem in hilly tracts. The weed also spreads through its seeds, which are minute and are carried by wind and water, as is Parthenium hysterophorus. Eichhornia crassipes, Salvinia molesta, Alternanthera philoxeroides and Ipomoea sp. are invaders of aquatic ecosystems and wetlands; these have done much harm to the biodiversity of aquatic ecosystems (Reddy, 2008). There are several attributes of invasive plant species that enable them to spread in alien environments (see Tables 1.2 and 1.3, respectively, for established invasive plants and those in the process of establishment). Some of the key features of invasive plants are discussed below.

4 4 R.K. Koh li et al. Table 1.1. Prominent invasive alien plants of the Indian subcontinent. Family name Botanical name (common name) Nativity Life form Amaranthaceae Amaryllidaceae Apocynaceae Araceae Asparagaceae Asteraceae Azollaceae Bignoniaceae Cabombaceae Convolvulaceae Chenopodium album (lamb's-quarters) Alternanthera philoxeroides (alligator weed) Zephyranthes citrina (yellow rain lily) Cryptostegia grandiflora (rubber vine) Pistia stratiotes (tropical duckweed) Asparagus densiflorus (asparagus fern) Ageratum conyzoides (billy goat weed) Ambrosia artemisiifolia (small ragweed) Anthemis cotula (stinking mayweed) Chromolaena odoratum (Siam weed) Cirsium arvense (creeping thistle) Eupatorium adenophorum (Crofton weed) Eupatorium cannabinum (hemp-agrimony) Gymnocoronis spilanthoides (Senegal tea plant) Leucanthemum vulgare (ox-eye daisy) Mikania micrantha (mile-a-minute weed) Parthenium hysterophorus (ragweed parthenium) Sphagneticola trilobata (Singapore daisy) Synedrella Walls (straggler daisy) Tagetes minuta (Mexican marigold) Azolla pinnata (mosquito fern) Macfadyena unguis-cati (cat's claw vine) Cabomba caroliniana (green cabomba) Ipomoea aquatica (water spinach) Central, S. Madagascar South Africa USA, Canada, Mexico Central, S. Central British Isles Central, S. Central Non-specific Central China Aquatic herb Vine-climber Vine/climber Climber Climber Merremia peltata (merremia) Africa Climber Elaeagnaceae Euphorbiaceae Fabaceae Hydrocharitaceae Limnocharitaceae Melastomataceae Moraceae Myrtaceae Onogranaceae Poaceae Pontederiaceae Rubiaceae Salviniaceae Solanaceae Elaeagnus umbellata (Japanese silverberry) Ricinus communis (castor bean) Sapium sebiferum (Chinese tallow) Acacia farnesiana (sweet acacia) Acacia mearnsii (black wattle) Acacia melanoxylon (blackwood acacia) Leucaena leucocephala (wild tamarind) Mimosa diplotricha (giant sensitive plant) Mimosa pudica (touch-me-not) Prosopis juliflora (mesquite) Ulex europeus (gorse) Hydrilla verticillata (water thyme) Limnocharis flava (yellow velvetleaf) Clidemia hirta (Koster's curse) Miconia calvescens (velvet tree) Broussonetia papyrifera (paper mulberry) Eugenia uniflora (Surinam cherry) Psidium guajava (apple guava) Ludwigia peruviana (Peruvian primrose willow) Arundo donax (giant cane) Imperata cylindrica (Cogon grass) Paspalum vaginatum (seashore paspalaum) Pennisetum clandestinum (Kikuyu grass) Phalaris arundinacea (reed canary grass) Spartina altemiflora (smooth cord grass) Eichhornia crassipes (water hyacinth) Coffea arabica (Arabic coffee) Coffea canephora (robusta coffee) Salvinia molesta (water fern) Physalis peruviana (cape gooseberry) Solanum mauritianum (wild tobacco tree) Solanum sisymbriifolium (sticky nightshade) Solanum viarum (tropical soda apple) China, Korea, Japan North-eastern Africa China Trop. Australia Australia Trop. Central, S. Asia, North Australia China Central, S. Indian subcontinent Asia/Africa? North Africa Africa Africa /shrub /shrub /shrub Climber/shrub

5 Plant Invasion in India 5 Table 1.2. Attributes of selected established invasive plants in India. Plant Ageratum conyzoides Parthenium hysterophorus Lantana camara Chromolaena odorata Country of origin Pathway of invasion Unknown, probably as ornamental Food grains Introduced as ornamental Introduced as ornamental Mikania macrantha Brought for camouflaging army during WWII Eichhornia crassipes Ornamental aquatic plant Alternanthera philoxeroides Salvinia molesta Accidently, as contaminant South, Accidental/ ornamental Invasive potential Fast-growing herb; aggressive stolon formation; high regenerative and reproductive potential through large number (ay. 94,772/plant) of minute, lightweight seeds, bearing pappi that help in dispersion through wind; wide ecological amplitude; strongly allelopathic Fast-growing herb; wide ecological amplitude; high regenerative and reproductive potential through large number of minute seeds (15,000/plant) dispersed through wind, water, biotic factors and transport; strongly allelopathic by habit; flowers exhibit genetic variations; forms suckers; high reproductive and regenerative potential; produces numerous seeds disseminated by birds, animals and even humans; wide ecological amplitude; strongly allelopathic Highly vigorous; high regenerative and reproductive potential; prolific seed producer (260,000/m2) with prolonged viability Vigorous, rampant growth; produces 40,000 seeds/year; spreads vegetatively by rooting at nodes Spreads fast due to quick vegetative (stolons) and sexual reproduction in water bodies Aquatic herb, spreads through vegetative reproduction by formation of fragmentation and axillary buds Reproduces very fast, mostly vegetatively by fragmentation Fast growth and reproduction: invasive alien plants often have better growth and reproductive traits, and thus they spread very fast in the invaded region. They often have either high regenerative potential (Parthenium hysterophorus) or special organs for vegetative reproduction, such as stolons (Ageratum conyzoides), root suckers (Lantana camara), rhizomes, bulbs or turions. Ability to adapt to diverse environmental conditions: invasive plants have high ecological amplitude and thus have enormous adaptability to a wide range of environmental conditions. These can survive under stressed conditions and they also have the ability to modify growth patterns in response to changing environments such as soil condition, moisture status or limited space availability.

6 6 R.K. Koh li et al. Table 1.3. Attributes of selected potential invasive plants in India in the early stages of establishment. Plant Leucaena leucocephala Broussonetia papyrifera Tagetes minuta Prosopis juliflora Sapium sebiferum Synedrella nodiflora Anthemis cotula Potamogeton crispus Imperata cylindrica Galinsoga ciliata Mimosa invisa Tithonia diversifolia Eupatorium riparium Country of Pathway of origin invasion Invasive potential Agroforestry/social forestry China, Japan Avenue tree Essential oils China, Japan, S. Africa Eurasia, Africa, Australia, N. SE Asia - Timber Avenue tree Aquatic weed Unknown Unknown By tea gardeners for soil enrichment Ornamental Self-fertile and produces large number of seeds growing in vicinity of parent plant forming monoculture; ability to re-sprout after cutting; seed production through year Prolific growth, multiplying rapidly vegetatively by suckering activity of root system Spreads very fast by seeds and forms huge populations showing vigorous growth Spread rapidly due to aggressive growth Spreads very fast by suckers, re-sprouts very rapidly and produces large number of seeds over a year with effective dispersal Spreads through seed dispersal Spreads through seed dispersal Tolerance to low light and low water temperature allows it to outcompete native plants; spread by plant fragments attached to water craft Aggressive and invasive nature is attributed to its rhizome, which produces numerous buds that sprout into new shoots Rapid establishment of weed is due to: (i) production of large number of seeds in a wide range of environmental circumstances; and (ii) vegetative reproduction Spreads very fast through seeds that remain dormant for up to 50 years Spreads through seed dispersal and vegetatively from basal stem Spreads through seed dispersal Absence of natural enemies or predators: invasive alien plants in new geographical areas are devoid of their natural predators or pests that co-evolved with them in their native environment. In the absence of these enemies their populations grow unchecked. Consequently, these form huge monocultures. In fact, absence of natural enemies forms the basis of the Natural Enemies hypothesis, as proposed by Heirro and Callaway (2003). Competitive advantage on account of allelopathy: many invasive alien plants are allelopathic. In other words, they release toxic chemicals to the environment that in turn hamper the growth and establishment of native flora. Parthenium hysterophorus is a potent allelopathic plant (Kohli and Rani, 1994). Lantana camara and Ageratum conyzoides are likewise reported as being strongly allelopathic (Ambika et al., 2003; Kohli et al., 2006). In fact, the allelopathic nature of many invasive alien plants forms the basis for the Novel Weapon hypothesis (Heirro and Callaway, 2003).

7 Plant Invasion in India 7 Efficient seed dispersal mechanism: invasive alien plants have a better and more efficient mechanism of dispersal of their seeds or propagules, by virtue of which these spread very rapidly from one place to another. Potential Invasive Plants in the Process of Establishment There are several plants that have not proved especially harmful to date but which possess the potential to become serious invaders. Early warnings regarding these species may help in managing them well before they damage natural ecosystems. Tagetes minuta, a native of, was introduced to various parts of the world, including India, for essential oils and medicinal value. However, it has been reported to be a noxious and invasive weed at many sites (Soule, 1993; Holm et al., 1997). In India it seems to have spread from cultivated areas, as it can be seen growing luxuriantly in disturbed sites in the north-western parts of the country (personal observation of the authors). Anthemis cotula, an ornamental plant from, is now spreading fast in the Kashmir valley - a Himalayan biodiversity hot spot (Shah and Zafar, 2007). Leucanthemum vulgare, another ornamental plant from, is also spreading rapidly in this valley and inhibiting the regeneration of the native forest floor vegetation (Khuroo et al., 2010). Jaryan et al. (2007) reported that Sapium sebiferum, a woody perennial, has the tendency to become invasive, particularly in the Himalayan region. Broussonetia papyrifera, commonly known as paper mulberry -a shrubby deciduous tree of Asian origin, possesses an invasive character and is spreading rapidly in the city of Chandigarh, India (personal observation of the authors). Management Tools When looking at the alarming rate at which invasive plants are spreading in India and also worldwide, effective management measures are required to control them. There are separate ways of dealing with those already established and those possessing the potential to be invasive but not of immediate risk. Above all, preventive measures are of utmost importance and require great attention at every level to prevent the entry of invasive species. Management of potential invasive species Environment Impact Assessment of introduced plants could be very useful in managing invasive species in the initial stages of their establishment. Gathering information regarding the pathways of invasion of potential invasive species; appropriate steps can be taken to prevent the entry of potential invasive plants based on this information. Following the international standards and quarantine measures based on the International Plant Protection Convention (IPCC) or the Convention on International Trade on Endangered Species of Flora and Fauna (CITES) to prevent the entry of potential plant invaders. Further information regarding these can be obtained from international organizations on invasive species such as The Global Invasive Species Programme ( IUCN's Invasive Species Specialist Group ( and its Global Invasive Species Database (GISD). Creating adequate awareness of the public about potential invasive plants and their management. To this end, online websites, scientific documents and books containing information on invasive plants could be quite useful. Success stories on control of weeds like Parthenium hysterophorus can also be used for dissemination of information (Batish et al., 2004). Management of established species Management of established invasive plants is very difficult. Based on the local situation,

8 8 R.K. Koh li et al. geographic region and climatic conditions, various methods such as physical, biological, chemical or cultural methods have been suggested, but these are of limited use. It is thus very important to follow an integrated approach and common interactive protocols for the management of invasive plants across the world. Some suggestions that may help in the management of invasive plants are listed below. understanding the life history of invasive plant species and their phenology, to help in devising control measures for their management; studying the ecology and biology of invasive plants, with special reference to their reproductive biology, dispersal ability and efficiency; understanding various biotic and abiotic factors limiting the growth of such plants; pests/pathogens of such plants can be explored from their native countries for their biological control; mass awareness programmes through booklets/pamphlets containing information on established local invasive species to discourage their further spread; and management, in a coordinated manner, through involvement of the general public and government officials or policy makers. Conclusions and the Way Forward From the above discussion, it is clear that a number of invasive plants have become established in India and several others are in the process. These cause major environmental, socio-economic and health-related harms to the native people, and it is thus important to take the following steps. Prepare a list of invasive plant species and gather comprehensive information on their status, pathways of entry and spread. Determine means of spread of invasive plants in order to prevent their further spread. Determine the environmental and socioeconomic impact of the invasive plants and devise management tools for their control. References Ambika, S.R., Poornima, S., Palaniraj, R., Sati, S.C. and Narwal, S.S. (2003) Allelopathic plants. 10. Lantana camara L. Allelopathy Journal 12, Aneja, K.R., Dhawan, S.R. and Sharma, A.B. (1991) Deadly weed Parthenium hysterophorus L. and its distribution. Indian Journal of Weed Science 23, Batish, D.R., Singh, H.P., Kohli, R.K., Johar, V. and Yadav, S. (2004) Management of invasive exotic weeds requires community participation. Weed Technology 18, Charles, H. and Dukes, J.S. (2007) Impacts of invasive species on ecosystem services. In: Nentwig, W. (ed.) Biological Invasions (Ecological Studies, Vol. 193). Springer-Verlag, Berlin, pp Drake, J.A., Mooney, H.A., di-castri, F, Groves, R.H., Kruger, F.J. and Rejmanek, M. (1989) Biological Invasions: A Global Perspective. John Wiley and Sons, Chichester, UK. GISD (2010) Global Invasive Species Database. Available online at Heirro, J.L. and Callaway, R.M. (2003) Allelopathy and exotic plant invasion. Plant and Soil 256, Herron, P.M., Martine, C.T., Latimer, A.M. and Leicht-Young, S.A. (2007) Invasive plants and their ecological strategies: prediction and explanation of woody plant invasion in New England. Diversity and Distributions 13, Holm, L., Doll, J., Holm, E., Pancho, J. and erger, J. (1997) World Weeds. Natural Histories and Distribution. John Wiley and Sons, Inc., New York. Jaryan, V., Chopra, S., Uniyal, S.K. and Singh, R.D. (2007) Spreading fast yet unnoticed: Are we in for another invasion? Current Science 93, Khuroo, A.A., Rashid, I., Reshi, Z., Dar, G.H. and Wafai, B.A. (2007) The alien flora of Kashmir Himalaya. Biological Invasions 9, Khuroo, A.A., Malik, A.H., Reshi, Z.A. and Dar, G.H. (2010) From ornamental to detrimental: plant invasion of Leucanthemum vulgare Lam. (Ox -eye Daisy) in Kashmir valley, India. Current Science 98,

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