By Vipin Kumar
Urban development for the provisioning of shelter to the ever increasing population transforms agricultural land into concrete jungles, and forests into agricultural land, thereby causing habitat degradation and fragmentation. This increases the extinction rate of wild flora and fauna several folds. This geographical landscape disturbance also results in nutrient cycle disturbance and accumulation of hazardous material in the air, soil and water, making them unfit for living beings. Surprisingly, these disturbed areas provide a conducive environment to alien species which go on to form monocultures by outcompeting native plants, causing great damage in non-native ranges (Lodge 1993). After habitat destruction, plant invasion is the second biggest threat to biodiversity.
Alien species are non-native or exotic organisms that occur outside their natural adapted ranges (Vermeij 1996), having high dispersal potential. Some of the alien species become invasive when they are introduced deliberately or unintentionally outside their natural habitats, in new areas where they express the capability to establish, invade and out compete native species (Sharma et al. 2005a). In order to become ‘invasive’, a species has to overcome a range of barriers, from individual level to population level, at each stage of survival.
Figure 1. Diagrammatic representation of generalised phases of invasion (Source: Sharma et al. 2005, Current Science).
Invasive plant species generally have some unique traits in comparison to native flora. For example, their growth rate is fast and the chances of ecological adaptability is high, enabling them to withstand environmental stresses in an alien environment. Interestingly, invasive species possess the ability to complete their vegetative phase in the shortest possible time period, allowing them to attain early maturity. Each plant has a different quest for its growth and survival, thus expressing different traits which are decisive in the degree of invasiveness they possess. So, to categorize a species as an ‘invasive’, and design strategies for its effective control, it is extremely important to explore the traits which provide an aid to its invasiveness.
Figure 2. Prosopis juliflora and Ricinus communis thriving at the verge of a railway track near Punjabi Bagh, Delhi.
Figure 3. Similarily Ricinus communis patches were found in between park and road near Naraina, Delhi.
Unproductive patches near construction sites, and road and railway lines are the potential sites which promote primary establishment of alien plants. It was observed that after their establishment, the alien species start propagating and disperse over long distances. Moreover, they outcompete the native species, and result in imbalances in the ecosystem that consequently lead to environment degradation.
Figure 4. Antigonon leptopus establishment near a housing society of Police Colony, Kingsway Camp, Delhi.
Studying morphological and physiological traits of alien plants, and environment exploration will assist conservation of biodiversity and provision of ecosystem services in urban environments (Williams et al. 2015). Thus, it is suggested that alien species that exploit habitats like those near city centers should be suppressed. Due to low competition from native plants in these disturbed habitats, it is advantageous to suppress invasive plants in these spaces. Tajerova et al. 2017 also suggested that management of habitats itself is a vital tool to control invasive plants.
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Sharma, G.P., Singh, J.S., & Raghubanshi, A.S. (2005a). Plant invasions: Emerging trends and future implications. Current Science, 88, 726–734
Vermeij, G.J. (1996). An agenda for invasion biology. Biological Conservation, 78, 3-9
Williams, N.S.G., Hahs, A.K., Vesk, P.A. (2015) Urbanisation, plant traits and the composition of urban floras. Perspect Plant Ecol Evol Syst 17:78–86
Tajerova, K.S., Petr, S., Milauer, P.S., Bruna, J.,Pysˇek, P. Landscape Ecol (2017) 32:681–692