Invasive Alien Species of Terrestrial Vegetation of North-Eastern Uttar Pradesh

The vegetational landscape of north-eastern Terai region at the foot hills of Central Himalayas is a mosaic of grassland, old-field, wasteland, and forest ecosystems. Like many other parts of the country, this region is also infested with alien intruders which not only interferewith the growth and production of food crops but also exercise adverse effects on the biodiversity of native species.The present study attempts to catalogue the invasive alien species of the terrestrial vegetation of north-eastern Uttar Pradesh especially with reference to their habit, taxonomic position, and nativity. A total of 1135 plant species within 580 genera under 119 families are so far known to occur in the region. Of these, only 149 species within 100 genera under 41 families have been found to be invasive aliens as evident from their center of origin, past history, nature of aggregation, and invasion observed under field conditions. About 80% of these invaders have been introduced from neotropics. Out of 173 invasive plants across India, this region shares 149 species, out of which 66% of species have come from Tropical America, 14% from African continent, and the rest from other countries. A better planning in the form of early identification and reporting of infestation and spread of noxious weeds is needed for their control.


Introduction
Invasion of alien plant species in recent times has been recognized as the second worst threat after habitat destruction [1].The International Union for Conservation of Nature and Natural Resources (IUCN) defines "alien invasive species" as an alien species which becomes established in natural or seminatural ecosystems or habitat as agent of change and threatens native biological diversity.Identifying the processes that determine the distribution and diversity of exotic species is a major area of research in ecology because exotics impose significant economic, social, and environmental costs, including human health [2].Biological invasion may be considered as a form of biological pollution and the significant component of anthropogenic changes leading to extinction of native species.The ecological approach to plant invasion has been mostly based on (a) biological and ecological features promoting the invasion success of particular species [3,4] and (b) the character and invasibility of invaded communities [5].Recently, both approaches are treated as complementary [6,7].The phytogeographical and floristic approaches are important for research on alien plants [8].A number of workers have studied and provided catalogues of the invasive alien plant species in different parts of the world [9][10][11][12].Establishment of a database of naturalized species is the first step in the development of invasion biology.A naturalized species is an introduced species that can consistently reproduce and sustain population over many generations without direct intervention by humans [13,14].After successful establishment few naturalized species disperse and produce viable offsprings in areas far from the sites of their introduction.Such naturalized species are then called invasive.It is estimated that as many as 50% of invasive species, in general, can be classified as ecologically harmful [13].
Due to increasing trade and transcontinental transport, the floras of Indian subcontinent have a number of alien species from various parts of the world as evident from the studies made at different parts in India, namely, Upper Gangetic Plain [15,16], Khandwa Plateau [17], Kodaikanal and Palani Hills [18], Kashmir Himalaya [19,20], Ranchi [21], Gangtok [22], Allahabad [23], Rajasthan [24], South Gujarat [25], and Doon Valley [26].This paper presents observations on the habit and nativity of invaders of north-eastern Uttar Pradesh and their impact on the diversity of native plants.

The Site, Climate, and Vegetation
The study was conducted in the Terai landscape of northeastern Uttar Pradesh.This area is characterized by even topography and fine alluvial deposits from Rapti and Gandak rivers.Mean altitude of the study area is 95 m amsl.The region slopes gently from north-west to south-east direction.Administratively the study area (∼10,000 km 2 ; 27 ∘ 5  to 27 ∘ 40  N latitude and 83 ∘ 30  to 84 ∘ E longitude) falls in Gorakhpur district of Uttar Pradesh state.It is bounded by Nepal in the north and Bihar state of India in the east.The landscape comprises a mosaic of human habitations, agricultural fields, grasslands, commercial plantations, and forests.The climate is typically monsoonic with three distinct seasons, namely, summer (March to mid-June), rainy (mid-June to mid-October), and winter (mid-October to February).The total average annual rainfall is about 1814 mm; about 87% of annual rainfall is received during warm rainy season and the rest 13% is distributed in the form of occasional showers from November to May.Relative humidity ranges between 74 and 87%.The mean maximum temperatures during wet summer, winter, and dry summer season are 35.2∘ , 27 ∘ , and 24-39 ∘ C and mean minimum temperatures are 26.2 ∘ , 12.1 ∘ , and 24.2 ∘ C, respectively (based on climatic data for [2000][2001][2002][2003][2004][2005].The soil of the region is classified as Gangetic alluvium, ranging from clayey to sandy loam in texture with pH ranging from 6.5 to 7.5.In the northern area there are a few elevated mounds, locally called dhus, which range in size from a few hundred meters to 4-5 km and have brown sandy soil.

Data Sources and Methods
Over the period between 1960 and 2013, a comprehensive list of invasive alien plant species of north-eastern Uttar Pradesh was made.The truly aquatic plants were avoided but marshy plants were considered as component of terrestrial vegetation.Several extensive reviews on invasive plant species are available [12,[27][28][29][30][31][32][33].The website http://www.isws.in/invasive-plants-of-india.php[34] was also searched for information on the origin and nativity of these invaders.Some information pertaining to the nativity of the species in India has been extracted from 18, 21-24, and 36-40.
Invasive alien species occurring in this region were compiled based on the literature survey, field observation, and discussion with local people.They were divided into three categories: naturalized, interfering, and noxious.Self-replacing plant populations by recruitment through seeds/ramets and capable of independent growth were categorized as naturalized.Alien and native plants which impacted agriculture adversely especially on the disturbed sites were taken as noxious.The adverse impact of noxious species was in the form of competition for space with tillage or forage crops and harbouring of pests or disease vectors, harmful to crops/native species.In addition to efficient vegetative mode of propagation the seeds of these species are mostly wind-distributed and may remain viable for several years.The species which were neither injurious nor noxious but caused profuse interference and hindrance to the growth of crop/native species over a large area by virtue of their vast numbers were taken as interfering.

Results
A total of 149 species of invasive aliens of the terrestrial vegetation of north-eastern Uttar Pradesh have been documented.These 149 alien species belonged to 100 genera under 41 families.The alien species amounted to 13.1% of 1135 wild terrestrial plant species of the region.The habit, nativity, and the impact of invasive species on forest, grassland, and agricultural communities were noticed to prepare a catalogue of invasive alien/exotic plant species (Table 1). 100 aliens have their origin in Tropical America compared to 21 species in African continent.About 28 species of alien plants reached the study area from such far off places as Afghanistan, Australia, Brazil, East Indies, Europe, Madagascar, Mascarene Islands, Mediterranean, Mexico, Peru, Temperate South America, Tropical West Asia, West Indies, and Western Europe.

Discussion
Alien species are nonnative or exotic organisms that occur outside their natural adapted ranges and dispersal potential   [35].These invasive species 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 [36].Many alien plant species support our farming and forestry systems in a big way.However, some of these aliens 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 outcompete native species [37].An important requirement for successful colonization of invaders is open habitat with reduced competition.Generally, the microsites created by grazing may be occupied by invader species [38][39][40].The invaders usually dominate the highly disturbed and man-made landscapes.So far, no ready hand catalogue of invasive species is available for this region.The present catalogue of invasive exotic species is likely to serve as basic information for future research towards conservation of native plant species of the region.
As evident from the data, the vegetation of northeastern Uttar Pradesh shows greater incidence of invaders as compared to the whole of Uttar Pradesh [41] and India [42].Reddy documented all invasive plant species irrespective of their habitat and use.In the present case, however, only the wild invasive plant species of terrestrial vegetation were considered and truly aquatic and ornamental invasive species were excluded.Many species, recorded as invader of northeastern Uttar Pradesh, are common to Indian Himalayan region and the whole of Uttar Pradesh.For example, 103 invaders are common to the whole of the state of Uttar Pradesh [41] and 95 species to the whole of India [42].Among the invasive species of north-eastern Uttar Pradesh, 70.5% are native to American continent.Other such studies vary slightly in percent share of tropical American nativity.While Singh et al. [41] reported 73% of invasive plant species of Uttar Pradesh, for Indian Himalayan region, however, Sekar [43] also noticed 73% invaders of American nativity.Reddy [42] noticed 58% of the invasive flora of India to be natives of American continent.
Alien species have been classified into naturalized and noxious species by various workers [13,44,45] [41,46,47].Further, some of these species are known to be highly allergic, causing diseases in human beings [48,49].Since they are rarely palatable, their dominance drastically reduces the number of grazers by way of reducing the carrying capacity of the pasture and wasteland [40].Datura innoxia and Datura stramonium are serious threat to the native species of the region and are known to cause delay in seedling growth of neighbouring plants [50].Leucaena leucocephala alters the natural growth of native plants because not only it obstructs plenty of sunlight to reach surface layer but also its allelopathic exudates cause retardation in seedling growth of neighbouring plants [51].Mikania micrantha could climb trees and cover the whole habitats through fast vegetative propagation and could also suppress the growth of crops and natural vegetation through competition and allelopathic effects [45].These species occur as invasive species under shifting agriculture in north-eastern Uttar Pradesh and combine an effective seed based reproduction with clonal propagation [52].Many invasive species such as species of Eupatorium tend to respond to temporarily nutrientenriched soil substrata and grow and quickly cover the gaps in disturbed forests.They can destroy arable soil, negatively affect the growth of orchard, and could also supplant grasses in pasture, excreting a toxic volatile that prevents grazing [48].
The herbaceous invasive plant species were recorded as the dominant invasive flora (80%) of north-east Uttar Pradesh, in the form of 119 invasive species.The greater viability and tolerance to harsh conditions could result in the preponderance of herbs across the region.Invasive species of Asteraceae exhibited a much higher reproductive capacity than those of other families.This high reproductive potential is achieved by partitioning of reproductive capital into a large number of propagules that are minute, light, and wind dispersed [53].Various other workers have also reported the dominance of Asteraceae among invasive alien species in Uttar Pradesh [41] and in Indian Himalayan region [43].
The invasive species cause loss of biodiversity through species extinction and their impact on ecosystem function.Differences between native and invasive plant species in their resource acquisition and consumption may cause a change in soil structure, decomposition, and nutrient content of the soil.Thus, invasive species are a serious hindrance to conservation with significant undesirable impacts on the goods and services provided by ecosystems.Biological invasions now operate on a global scale and are likely to undergo rapid increase in this century due to interaction with other changes such as increasing travel and tourism.A quick monitoring of invasion can, therefore, be done through qualitative approach like species inventory method.

Conclusion
Plant invasions in the new areas alter indigenous community composition, deplete species diversity, affect ecosystem process, and thus cause huge economic and ecological imbalance.A quick inventory and plant identification network are, therefore, needed for early detection and reporting of noxious and naturalized weeds in order to control the spread of invasive plant species.

Figure 1 :
Figure 1: Families accounting for >5 speciesinvasive in the terrestrial vegetation of north-eastern Uttar Pradesh.

Figure 2 :
Figure 2: Number (%) of plant invasive species under different habit categories within terrestrial vegetation of north-eastern Uttar Pradesh.

Figure 3 :
Figure 3: Species number under three different categories of invasive plants.

Table 1 :
Wild invasive plant species in terrestrial vegetation of north-eastern Uttar Pradesh.