The 22nd day of the month of May is celebrated every year as the International day for biological diversity. It is a United Nations–sanctioned international holiday for the promotion of biodiversity issues. Biological diversity includes all life on earth and comprises of not only the plants and animals that we see but also the microscopic organisms that live in the soil, the bacteria in our digestive tracts, and the myriad biological processes that sustain life on earth. Biodiversity can be broadly classified into three types:
1. Genetic biodiversity: Diversity within a species having two key characteristics, the capacity to evolve and the molecular information held in genepools.
2. Species biodiversity: Diversity between species referred to as the combined measure of the number of species and the number of individuals in a species.
3. Ecosystem biodiversity: Refers to the diversity within and between different ecosystems.
The theme for the International Day for Biological Diversity (IDB) in 2009 is invasive alien species (IAS) - one of the greatest threats to bio-diversity, and to the ecological and economic well-being of society and the planet.
Alien species are non-native or exotic organisms that occur outside their natural adapted ranges and dispersal potential. Many alien species support our farming and forestry systems in a big way. However, some of the alien species become invasive when they are introduced deliberately or unintentionally outside their natural habitats into new areas where they express the capability to establish, invade and out compete native species. International Union for Conservation of Nature and Natural Resources (IUCN) defines Alien Invasive Species as an alien species which becomes established in natural or semi natural ecosystems or habitat, an agent of change, and threatens native biological diversity. These invasives are widely distributed in all kinds of ecosystems throughout the world, and include all categories of living organisms. Nevertheless, plants, mammals and insects comprise the most common types of invasive alien species in terrestrial environments. The threat to biodiversity due to invasive alien species is considered second only to that of habitat destruction. Invasive species cause loss of biodiversity including species extinctions, and changes in hydrology and ecosystem function. Differences between native and exotic plant species in their requirements and modes of resource acquisition and consumption may cause a change in soil structure, its profile, decomposition, nutrient content of soil, moisture availability, etc. Invasive species are thus a serious hindrance to conservation and sustainable use of biodiversity, with significant undesirable impacts on the goods and services provided by ecosystems. Biological invasions now operate on a global scale and will undergo rapid increase in this century due to interaction with other changes such as increasing globalization of markets, rise in global trade, travel and tourism. For effective management of invasive species, knowledge about their ecology, morphology, phenology, reproductive biology, physiology and phytochemistry is essential. About 40% of the species in the Indian flora are alien, of which 25% are invasive (Kavita Gupta; National Bureau of Plant Genetic Resources). A list of invasive alien species was presented during a national level workshop sponsored by the Ministry of Environment &Forests held at the Banares Hindu University. The workshop focussed on themes related with the ecology of alien invasive species such as: biology of invasive species, reasons behind invasiveness, prediction of invasive potential of non-native species, susceptibility of ecosystems to invasions, impact of invasion on native plant species and biodiversity, possibility of enhancing the capacity of ecosystems to resist or recover from alien species invasion, possible control measures and development of a reporting system for alien invasive species. The list of invasive species includes some species commonly found in Nagaland. They are Parthenium hysterophorus, Eupatorium adenophorum, Eupatorium odoratum, Ageratum conyzoides, and Lantana camera. A brief description of some of the above mentioned plants are given below:
1. Parthenium hysterophorus: It is an exotic species from Tropical America that has naturalized most of India because of its strong invasive potential. This weed was first reported in India in 1951 from Maharashtra.The weed is an aggressive colonizer of degraded areas with poor groundcover and exposed soil such as fallow wastelands, roadsides and overgrazed pastures. It does not usually become established in undisturbed vegetation or in vigorous pastures, and there is a marked inverse relationship between existing plant cover and native weed density. Parthenium hysterophorus is considered as a noxious weed because of its prolific seed production and fast-spreading ability, allelopathic effect on other plants, strong competitiveness with crops and health hazard to humans as well as animals. The weed is highly allergenic and causes respiratory problems, dermatitis and asthma. However, except for allelopathic aspect and crop–weed interaction, almost no study is available on the impact of this weed on the ecosystem processes.
2. Ageratum conyzoides : It is an annual weed native to South America that has invaded and now naturalized in several parts of southern Asia including India. The invasive potential of weed is attributed to its fast growth, production of large number of small-sized wind and water-disseminated seeds and vegetative proliferation through stolons. The weed has become a problem in agro ecosystems.
3. Lantana camera: It is one of the ten worst weeds of the world, which is a native of tropical and subtropical America. The species was introduced in India as an ornamental shrub during AD 1809–1810. It is now found all over the Indian sub-continent, stretching from the sub montane regions of the outer Himalaya to southernmost part of India. The plant is spreading fast due to the human disturbances such as cultivation, road construction and forest fragmentation and degradation. Important attributes of Lantana making it invasive includes fitness homeostatis, phenotypic plasticity, benefits from destructive foraging activities, widespread geographical range, vegetative reproduction capabilities, fire resistance, better competitive ability and allelopathy. Low allocation of biomass to roots, and low wood density enable it to rapidly establish aboveground plant cover. High nutrient extraction efficiency contributes to its colonization on the eroded sites with shallow soils.
little information exists regarding invasive fauna and microbes in India. There is a need of creating specialist groups in this regard so that better information can be compiled. The only fauna on which information is available is mosquito, several species of which is invasive and are spreading fast throughout the world.
Many of the invasive species can be used for economic benefits. Scientists have emphasized that economic valuation of most of the invasive species is due and should be done on priority basis. In this context, M. N. V. Prasad (University of Hyderabad) has worked on the use of metalliferous invasive species to cleanup metal-contaminated ecosystems. The knowledge of how metalliferous invasive plants can specifically accumulate or exclude essential elements, bioavailability of metals, rhizospheric processes as well as translocation and processing and storage in the plant parts is essential for proper utilization of these plants.
Department of Forests, Nagaland: Kohima.
