Alien Plant Invasion and Their Impact on Indigenous Species Diversity at Global Scale: a Review

Journal of Ecology and the Natural Environment Vol. 2(9), pp. 175-186, September 2010 Available online at http://www.academicjournals.org/jene ISSN 2006- 9847 ©2010 Academic Journals Review Alien plant invasion and their impact on indigenous species diversity at global scale: A review Kuldip S. Dogra1*, Sarvesh K. Sood1, Parveen K. Dobhal2 and Seema Sharma1 1Department of Biosciences, Himachal Pradesh University, Summer Hill, Shimla-171005, India. 2Department of Botany, Panjab University Chandigarh- 160014, India. Accepted 18 August, 2010 Plant invasion is a potent threat to the species diversity around the world during the 21st century after habitat loss. Plant invasions are human introduced or of natural means like winds, birds, animals, water. It affects indigenous species diversity, soil ecology and dynamics and economics of agricultural ecosystem throughout the world. If this process of biological invasion is remained continuous for years to come then we can only transfer monocultures of species to our future generations. To preserve our indigenous species diversity, it is important to understand the process of plant invasions and their impact on species diversity in various habitats around the world. Key words: Alien species, ecosystem, indigenous species, plant invasion. INTRODUCTION Invasion by the alien plant species were increased rapidly alien herbal plants increased in the areas of human throughout the world during the present century and interference such as forest fragmentation (Higgins et al., responsible for the homogenization of floras which 1996). causes a substantial threat to biodiversity and ecological Alien species that can rapidly achieve high densities integrity of native habitats and ecosystems (Booth et al., may have greater establishment success (Kolar and 2003; Hulme, 2003). Invasion by the species cause Lodge, 2001) and dominate invaded communities to the extensive effects on the habitats they invade, like impact exclusion of indigenous species (Ortega and Pearson, on indigenous species diversity, soil nutrient composition, 2005). The species capable of rapid colonization are, in altering forest fire cycles and loss of productivity of general, more likely to have negative impacts on invading ecosystems. It also becomes a threat to biodiversity (Callaway and Ridenour, 2004). It is endangered or threatened plant species around the world estimated that as many as 50% of invasive species in (Pimentel et al., 2005). It is supposed that 10% of plant general can be classified as ecologically harmful, based species, on an average, from any region are good on their actual impacts (Richardson et al., 2000). In India colonizers. Thus, it can be estimated that from 260,000 especially NW Himalaya Ageratum conyzoides L., vascular plant species known around the world, only 10% Parthenium hysterophorus L., Lantana camara L. and are potential invaders. Further, there are about 10,000 Eupatorium adenophorum Sp. (Syn. Ageratina recognized invasives and 40% of these have been adenophora (Spreng.) R. M. King and H. Rob.) are major interchanged among different regions of the world invaders and causing huge loss to indigenous species (Rapoport, 1991). It is also estimated that 20% or more of diversity in this part of the world (Dogra et al., 2009). In the plant species are exotics in many continental areas view of the increased threat of alien plant species, this and 50% or more on many islands (Rejmanek and paper presents an insight into the type of plant invasions Randall, 1994). The disturbances in the natural and their impact on species diversity throughout the world ecosystems provide the great opportunities to the alien in the last centaury. invaders to establish themselves. The frequency of the PLANT INVASIONS AND THEIR TYPE *Corresponding author. E-mail: [email protected]. Tel: Plant invasions dramatically affect the distribution, 919816740648, 919459170683. abundance and reproduction of many native species 176 J. Ecol. Nat. Environ. (Sala et al., 1999). Because of these ecological effects, this regard. It is reported that the introduction of this alien species can also influence the evolution of natives species in India occurred accidentally (Roxburgh, 1884; exposed to novel interactions with invaders (Parker et al., Bennet et al., 1976; Maiti, 1983) in 1810 and lived in 1999). Evolutionary changes in natives in response to obscurity until Rao reported it in 1956 from Pune. selection from aliens are usually overlooked, yet common However, its exponential spread was witnessed between responses include altered anti-predator defenses, 1985 and 1995 when it engulfed almost the whole of changes in the spectrum of resources and habitats used, India including NW Himalaya (Himachal Pradesh) up to and other adaptations that allow native populations to 2000 m (Dogra et al., 2009). persist in invaded areas (Mooney and Cleland, 2001). So, introduction of such invasive species leads to change in the structure and composition of native communities (Rice and Emery, 2003). It is basically of two types: IMPACT OF PLANT INVASIONS 1). Human introduced invasions Studies of past introductions demonstrate that the effects 2). Natural invasions of invasive species are complex and can permanently alter the structure of communities (Holway et al., 2002; Carlton, 2003). Invasive alien species pose a threat to Human introduced invasions native/indigenous plant communities globally, especially where these communities are disturbed (D’Antonio et al., The human-made introductions in the new habitats are 2001). However, relatively few alien plant species seem quick and responsible for rapid change within the to have the capacity to invade undisturbed native plant indigenous communities (Ridenour and Callaway, 2001). communities (Rejm´anek, 1989). In India A. conyzoides The introduction of plant species by humans increased L., P. hysterophorus L., E. adenophorum Sp. and L. during the last five centuries, especially during the camara L. are well recognized alien invaders which twentieth century, due to rapid increase in trade and posed threat to indigenous plant communities under travel across the globe. Planes, ships, and other forms of various habitats and areas from planes to hills (Table 1). modern transport have allowed both deliberate and inadvertent movement of species, often resulting in unexpected and sometimes disastrous consequences Impact on the natural plant species (Moore, 2004). Some times the species are introduced in such environments which can not be chosen by the species themselves for their growth and establishment. Disturbed and unattended habitats are more prone to the The introduction of new species in the balanced invasion as compare to the well-managed ecosystems ecosystems and habitats can affect the natural process and habitats. The habitats which have more diverse which leads towards destruction or loss of biodiversity communities are highly competitive and resist invasion (Louda et al., 2003). Introduction of Eucalyptus citriodora (Crawley, 1987). For example, direct competition with the Hook., Populus deltoides Marsh. and Lantana camara L. native flora can result in monocultures of an alien species in India is an example of human introduced species, such as by Psidium cattleianum Sabine invasions (Kohli et al., 2004; Dogra et al., 2009). (strawberry guajava) in Mauritius and P. hysterophorus L. (white top) in Australia and India (Evans,1997). The invasive trees introduced in Florida (USA) cause Natural invasions major threats to the native vegetation. The tree species included Brazilian pepper (Schinus terebinthifolius), The impact of natural invasion is almost similar to that of Australian paperbark (Melaleuca quinquenrvia) and human made invasions but this kind of invasion mostly Australian pine THAT IS Casuarina sp. (Schmitz et al., depends upon the dispersal ability of the invading plants 1997). Invasion by different pine species becomes a and animals. The time scale for natural invasion can problem to natural habitats in Australia, New Zealand, range from few years to several years. The sources for and South Africa (Richardson et al.,1994). It was reported natural invasion are birds, animals, water and wind etc that in Christmas Island (Australia) 52.70% species have (Herbold and Moyle 1986). Ageratum conyzoides L. and been found to be aliens (Claussen, 2001) and most of Parthenium hysterophorus L. are examples of such type them are confined to disturbed regions such as of invasions in India (Kohli et al., 2004; Dogra et al., minefields, overburden dumps, and road sides. These 2009). After natural invasion by an alien plant species, include Leucaena leucocephala, Muntingia calabura, there is a “lag phase” that may range from decades to Ricinis communis, Carica papaya and Psidium guajava centuries before an exponential phase of its fast spread (Green et al., 2004). (Ghate, 1991). The species that at a given time may The alien terrestrial invaders are responsible for appear to be non-invasive may suddenly begin to spread extensive and unpredictable irreversible changes to the rapidly. P. hysterophorus fits well as an example in this natural habitats (Higgins et al., 1999). Many exotic tree Dogra et al. 177 Table 1. Impact of some major invasive plants in India. Botanical, common name and habit S/No. Origin Threat Reference of alien plants 1 Ageratum conyzoides L. Tropical America Wastelands, plantations, pastures and Dogra et al., 2009 (Goat Weed) all forest types. Posing threat to Asteraceae indigenous

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