International Journal of Forestry Research

Volume 2014 (2014), Article ID 959875, 9 pages

http://dx.doi.org/10.1155/2014/959875

Research Article

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

Sumit Srivastava, Ashish Dvivedi, and Ravindra Prasad Shukla

Plant Ecology Laboratory, Department of Botany, DDU, Gorakhpur University, Gorakhpur 273009, India

Received 19 January 2014; Accepted 21 April 2014; Published 12 May 2014

Academic Editor: Robin Reich

Copyright © 2014 Sumit Srivastava et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

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 interfere with 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.

1. 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 [9–12]. 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.

2. The Site, Climate, and Vegetation

The study was conducted in the Terai landscape of north-eastern 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 km²; 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 2000–2005). 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.

3. 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, 27–33]. 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.

4. 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.

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

S. No.
Name of the Species
Family
Habit
Nativity
Categories

1
Acacia farnesiana (L.) Willd
Mimosaceae
Tree
Tropical South America
Naturalized

2
Acanthospermum hispidum DC.
Asteraceae
Herb
Brazil
Naturalized

3
Aerva tomentosa
Amaranthaceae
Herb
Tropical America
Naturalized

4
Ageratum conyzoides L.
Asteraceae
Herb
Tropical America
Noxious

5
Ageratum houstonianum Mill.
Asteraceae
Herb
Tropical America
Interfering

6
Alternanthera paronychioides A. St. Hill
Amaranthaceae
Herb
Tropical America
Naturalized

7
Alternanthera pungens Kunth
Amaranthaceae
Herb
Tropical America
Naturalized

8
Alternanthera sessilis (L.) R. Br. ex DC.
Amaranthaceae
Herb
Tropical America
Naturalized

9
Amaranthus spinosus L.
Amaranthaceae
Herb
Tropical America
Naturalized

10
Anagallis arvensis L.
Primulaceae
Herb
Europe
Naturalized

11
Antigonon leptopus Hook and Arn.
Polygonaceae
climber
Tropical America
Noxious

12
Argemone mexicana L.
Papaveraceae
Herb
Tropical South America
Noxious

13
Argemone ochroleuca Sweet.
Papaveraceae
Herb
Mexico
Interfering

14
Asphodelus tenuifolius Cav.
Liliaceae
Herb
Tropical America
Naturalized

15
Blainvillea acmella (L.) Philipson
Asteraceae
Herb
Tropical America
Interfering

16
Blumea eriantha DC.
Asteraceae
Herb
Tropical America
Interfering

17
Blumea lacera (Burm f.) DC.
Asteraceae
Herb
Tropical America
Interfering

18
Blumea obliqua (L.) Druce
Asteraceae
Herb
Tropical America
Interfering

19
Borassus flabellifer L.
Arecaceae
Tree
Tropical Africa
Naturalized

20
Calotropis gigantea (L.) R. Br.
Asclepiadaceae
Shrub
Tropical Africa
Interfering

21
Calotropis procera (Ait) R. Br.
Asclepiadaceae
Shrub
Tropical Africa
Interfering

22
Cannabis sativa L.
Cannabaceae
Herb
Central Asia
Interfering

23
Cassia absus L.
Caesalpiniaceae
Herb
Tropical America
Naturalized

24
Cassia alata L.
Caesalpiniaceae
Shrub
West Indies
Naturalized

25
Cassia hirsute L.
Caesalpiniaceae
Herb
Tropical America
Naturalized

26
Cassia obtusifolia L.
Caesalpiniaceae
Herb
Tropical America
Naturalized

27
Cassia occidentalis L.
Caesalpiniaceae
Herb
Tropical South America
Naturalized

28
Cassia pumila Lam.
Caesalpiniaceae
Herb
Tropical America
Naturalized

29
Cassia tora L.
Caesalpiniaceae
Herb
Tropical South America
Noxious

30
Celosia argentea L.
Amaranthaceae
Herb
Tropical Africa
Naturalized

31
Chenopodium album L.
Chenopodiaceae
Herb
Europe
Interfering

32
Chenopodium ambrosioides L.
Chenopodiaceae
Herb
Tropical America
Interfering

33
Chenopodium murale L.
Chenopodiaceae
Herb
Tropical America
Naturalized

34
Chloris barbata Sw.
Poaceae
Herb
Tropical America
Naturalized

35
Chrozophora rottleri (Geis) Spring
Euphorbiaceae
Herb
Tropical Africa
Naturalized

36
Cleome burmanni
Capparidaceae
Herb
West Africa
Naturalized

37
Cleome gynandra L.
Capparidaceae
Herb
Tropical America
Naturalized

38
Cleome rutidosperma DC.
Capparidaceae
Herb
Tropical America
Naturalized

39
Cleome viscosa L.
Capparidaceae
Herb
Tropical America
Naturalized

40
Clerodendrum splendens G. Don
Verbenaceae
Climber
Africa
Interfering

41
Convolvulus arvensis L.
Convolvulaceae
Herb
Europe
Naturalized

42
Corchorus aestuans L.
Tiliaceae
Herb
Tropical America
Naturalized

43
Corchorus fascicularis Lam.
Tiliaceae
Herb
Tropical America
Naturalized

44
Corchorus olitorius L.
Tiliaceae
Herb
Tropical Africa
Naturalized

45
Coronopus didymus (L.) Smith
Brassicaceae
Herb
Tropical America
Interfering

46
Crotalaria mucronata.Ait
Papilionaceae
Herb
Tropical America
Interfering

47
Croton bonplandianum Boil.
Euphorbiaceae
Herb
Temperate South America
Naturalized

48
Cryptostegia grandiflora R. Br.
Asclepiadaceae
Herb
Madagascar
Interfering

49
Cuscuta reflexa Roxb.
Cuscutaceae
Herb
Mediterranean
Interfering

50
Cynodon dactylon (Linn.) Pers
Poaceae
Herb
Africa
Naturalized

51
Cyperus difformis L.
Cyperaceae
Herb
Tropical America
Naturalized

52
Cyperus flabelliformis Rottb.
Cyperaceae
Herb
Africa
Interfering

53
Cyperus iria L.
Cyperaceae
Herb
Tropical America
Naturalized

54
Cyperus cyperoides L.
Cyperaceae
Herb
Tropical America
Naturalized

55
Datura innoxia Mill.
Solanaceae
Shrub
Tropical America
Noxious

56
Datura metel L.
Solanaceae
Shrub
Tropical America
Interfering

57
Datura stramonium L.
Solanaceae
Shrub
Tropical America
Noxious

58
Digera muricata (L.) Mart
Amaranthaceae
Herb
South-West Asia
Interfering

59
Duranta repens Linn.
Verbenaceae
Shrub
America
Naturalized

60
Echinochloa colonum (L.) Link
Poaceae
Herb
Tropical South America
Naturalized

61
Echinochloa crus-galli (L.) Beauv.
Poaceae
Herb
Tropical South America
Noxious

62
Echinops echinatus Roxb.
Asteraceae
Herb
Afghanistan
Naturalized

63
Eclipta prostrata (L.) Mart.
Asteraceae
Herb
Tropical America
Naturalized

64
Emilia sonchifolia (L.) DC.
Asteraceae
Herb
Tropical America
Naturalized

65
Erigeron bonariensis L.
Asteraceae
Herb
South America
Interfering

66
Eupatorium adenophorum Sprengel
Asteraceae
Shrub
Mexico
Noxious

67
Eupatorium odoratum L.
Asteraceae
Shrub
Tropical America
Interfering

68
Euphorbia chamaesyce L.
Euphorbiaceae
Herb
West Africa & Mauritius
Naturalized

69
Euphorbia hirta L
Euphorbiaceae
Herb
Tropical America
Naturalized

70
Euphorbia  heterophylla L.
Euphorbiaceae
Herb
Tropical America
Naturalized

71
Evolvulus nummularius(L.) L.
Convolvulaceae
Herb
Tropical America
Naturalized

72
Flaveria trinervia (Spreng.) C. Mohar
Asteraceae
Herb
Tropical Cent. America
Naturalized

73
Galinsoga parviflora Cav.
Asteraceae
Herb
Tropical America
Naturalized

74
Glossocardia bosvallia(L. f.) DC.
Asteraceae
Herb
West Indies
Naturalized

75
Gnaphalium polycaulon Pers.
Asteraceae
Herb
Tropical America
Interfering

76
Gomphrena celosioides Mart.
Amaranthaceae
Herb
Tropical America
Naturalized

77
Gomphrena globosa Linn.
Amaranthaceae
Herb
America
Naturalized

78
Grangea maderaspatana (L.) Poir.
Asteraceae
Herb
Tropical South America
Naturalized

79
Hyptis suaveolens (L.) Poit
Lamiaceae
Herb
Tropical America
Interfering

80
Imperata cylindrica (L.) Raensch.
Poaceae
Herb
Tropical America
Naturalized

81
Indigofera glandulosa Roxb. Ex Willd
Papilionaceae
Herb
Tropical America
Naturalized

82
Indigofera hirsuta Hook.
Papilionaceae
Herb
Tropical Africa
Naturalized

83
Indigofera linearis Ali
Papilionaceae
Herb
Tropical Africa
Naturalized

84
Indigofera linifolia (L. f.) Retz.
Papilionaceae
Herb
Tropical South America
Naturalized

85
Ipomoea eriocarpa R. Br.
Convolvulaceae
Climber
Tropical Africa
Interfering

86
Ipomoea fistulosa Mart DC.
Convolvulaceae
Shrub
Tropical America
Interfering

87
Ipomoea muricata L.
Convolvulaceae
Climber
Tropical America
Naturalized

88
Ipomoea nil (L.) Roth.
Convolvulaceae
Climber
North America
Naturalized

89
Ipomoea obscura (L.) Ker. Gawl.
Convolvulaceae
Climber
Tropical Africa
Interfering

90
Ipomoea pes-tigridis L.
Convolvulaceae
Climber
Tropical East Africa
Interfering

91
Ipomoea purpurea (Linn.) Roth
Convolvulaceae
Herb
America
Interfering

92
Ipomoea quamoclit L.
Convolvulaceae
Climber
Tropical America
Interfering

93
Jatropha curcas
Euphorbiaceae
Herb
Tropical America
Naturalized

94
Jatropha gossypifolia L.
Euphorbiaceae
Shrub
Brazil
Naturalized

95
Lagascea mollis Cav
Asteraceae
Herb
Tropical Cent. America
Noxious

96
Lantana camara L.
Verbenaceae
Shrub
Tropical America
Noxious

97
Leonotis nepetifolia (L.) R. Br.
Lamiaceae
Herb
Tropical Africa
Interfering

98
Leucaena leucocephala (Lam.) de. Wit
Mimosaceae
Herb
Tropical America
Noxious

99
Lippia alba
Verbenaceae
Herb
Trop. America & West Indies
Interfering

100
Ludwigia adscendens (L.) Hara
Onagraceae
Herb
Tropical America
Naturalized

101
Ludwigia octovalvis (Jacq.) Raven
Onagraceae
Herb
Tropical America
Naturalized

102
Ludwigia parviflora Roxb.
Onagraceae
Herb
Tropical Africa
Naturalized

103
Malvastrum coromandelianum (L.) Gar.
Malvaceae
Herb
Tropical America
Naturalized

104
Martynia annua L.
Pedaliaceae
Herb
Tropical America
Interfering

105
Mecardonia procumbens (Mill.) Small
Scrophulariaceae
Herb
Tropical North America
Naturalized

106
Melilotus alba Desv.
Papilionaceae
Herb
Europe
Naturalized

107
Melochia corchorifolia L.
Sterculiaceae
Herb
Tropical America
Naturalized

108
Merremia dissecta (Jacq.) Hallier f.
Convolvulaceae
Herb
Tropical America
Naturalized

109
Mikania micrantha Kunth.
Asteraceae
Climber
Tropical America
Noxious

110
Mimosa pudica L.
Mimosaceae
Herb
Brazil
Naturalized

111
Nicotiana plumbaginifolia Viv.
Solanaceae
Herb
Tropical America
Naturalized

112
Ocimum americanum L.
Lamiaceae
Herb
Tropical America
Naturalized

113
Opuntia elatior Mill.
Cactaceae
Herb
Tropical America
Noxious

114
Oxalis corniculata L.
Oxalidaceae
Herb
Europe
Naturalized

115
Oxalis corymbosa DC.
Oxalidaceae
Herb
South America
Naturalized

116
Parthenium hysterophorus L
Asteraceae
Herb
Tropical North America
Noxious

117
Passiflora foetida L.
Passifloraceae
Herb
Tropical South America
Interfering

118
Pedalium murex L.
Pedaliaceae
Herb
Tropical America
Naturalized

119
Peperomia pellucida (L.) Kunth.
Piperaceae
Herb
Tropical South America
Naturalized

120
Peristrophe paniculata (Forsk.) Brummitt
Acanthaceae
Herb
Tropical America
Interfering

121
Physalis minima L.
Solanaceae
Herb
Tropical America
Naturalized

122
Physalis peruviana L
Solanaceae
Herb
Tropical America
Interfering

123
Pilea microphylla
Urticaceae
Herb
Tropical South America
Naturalized

124
Portulaca oleracea L.
Portulacaceae
Herb
Tropical S. America
Naturalized

125
Portulaca quadrifida L.
Portulacaceae
Herb
Tropical America
Naturalized

126
Rauvolfia tetraphylla
Apocynaceae
Herb
West Indies
Naturalized

127
Ricinus communis Linn.
Euphorbiaceae
Shrub
Africa
Interfering

128
Rubus ellipticus Smith
Rosaceae
Shrub
Tropical America
Naturalized

129
Ruellia tuberosa L.
Acanthaceae
Herb
Tropical America
Naturalized

130
Saccharum spontaneum L.
Poaceae
Herb
Tropical West Asia
Interfering

131
Scoparia dulcis L.
Scrophulariaceae
Herb
Tropical America
Naturalized

132
Sesbania bispinosa (Jacq.) W. F. Wight
Papilionaceae
Shrub
Tropical America
Naturalized

133
Sida acuta Burm f.
Malvaceae
Herb
Tropical America
Naturalized

134
Solanum khasianum
Solanaceae
Herb
Tropical America
Interfering

135
Solanum nigrum L.
Solanaceae
Herb
Tropical America
Naturalized

136
Solanum torvum Sw.
Solanaceae
Shrub
West Indies
Interfering

137
Solvia anthemifolia (Juss) R.
Asteraceae
Herb
America
Interfering

138
Sonchus asper Hill.
Asteraceae
Herb
Mediterranean
Interfering

139
Sonchus oleraceus L.
Asteraceae
Herb
Mediterranean
Interfering

140
Synedrella nodiflora (L.) Gaertn.
Asteraceae
Herb
West Indies
Naturalized

141
Tithonia diversifolia (Hense) A. Gray
Asteraceae
Shrub
Mexico
Naturalized

142
Trema orientalis L.
Ulmaceae
Tree
Africa
Naturalized

143
Tribulus terrestris L.
Zygophyllaceae
Herb
Tropical America
Naturalized

144
Tridax procumbens L.
Asteraceae
Herb
Tropical Cent. America
Naturalized

145
Triumfetta rhomboidea Jacq.
Tiliaceae
Herb
Tropical America
Naturalized

146
Urena lobata L.
Malvaceae
Shrub
Tropical Africa
Interfering

147
Xanthium strumarium L.
Asteraceae
Herb
Tropical America
Noxious

148
Youngia japonica (L.) DC.
Asteraceae
Herb
Tropical South America
Naturalized

149
Zephyranthes candida Lindl.
Amaryllidaceae
Herb
America
Naturalized

The herbaceous elements predominated the regional alien flora. The number of dicot alien species was 136, under 93 genera and 32 families. On the other hand, there were only 13 species of monocot aliens distributed among 9 genera under 5 families (Amaryllidaceae, Arecaceae, Cyperaceae, Liliaceae, and Poaceae). Of 41 families having alien species, Asteraceae was the most dominant (29 species) followed by Convolvulaceae (11), Amaranthaceae and Solanaceae (9 species each), Euphorbiaceae (8), Caesalpiniaceae and Papilionaceae (7 each), Poaceae (6), Capparidaceae, Cyperaceae, Tiliaceae, and Verbenaceae (4 each), Asclepiadaceae, Chenopodiaceae, Lamiaceae, Malvaceae, Mimosaceae, and Onagraceae (3 each), Acanthaceae, Oxalidaceae, Papaveraceae, Pedaliaceae, Portulacaceae, and Scrophulariaceae (2 each), and Amaryllidaceae, Apocynaceae, Arecaceae, Brassicaceae, Cannabaceae, Cuscutaceae, Cactaceae, Liliaceae, Polygonaceae, Primulaceae, Passifloraceae, Piperaceae, Rosaceae, Sterculiaceae, Ulmaceae, Urticaceae, and Zygophyllaceae (1 species each). Of these aliens, 15 species were judged as noxious, 43 species as interfering, and 91 as naturalized species (Figure 1). Habit wise analysis shows that 80% of species are herbs, 12% are shrubs, 6% are herbaceous climbers, and 2% are trees (Figure 2). The eight dominant families contributed 47% of the invasive alien flora of wild terrestrial vegetation of north-eastern Uttar Pradesh (Figure 3).

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

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

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

5. 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 [38–40]. 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 north-eastern 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 north-eastern 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]. Our field observation and discussion with local people indicate that there are 15 most noxious invasive plant species in this region, namely, Ageratum conyzoides, Antigonon leptopus, Argemone mexicana, Cassia tora, Datura stramonium, Datura innoxia, Echinochloa crus-galli, Eupatorium adenophorum, Lantana camara, Lagascea mollis, Leucaena leucocephala, Mikania micrantha, Parthenium hysterophorus, Opuntia elatior, and Xanthium strumarium. Some species such as Ageratum conyzoides, Eupatorium adenophorum, Lantana camara, and Parthenium hysterophorus are harmful to native species [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 nutrient-enriched 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.

6. 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.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

The authors are thankful to the Head Department of Botany, D.D.U., Gorakhpur University, Gorakhpur, for providing access to departmental herbarium and other required facilities. They also feel grateful to the anonymous reviewer for his critical comments and suggestions to improve the quality and clarity of the content and to Dr. Robin Reich for very quick response.

References

C . B. D, “Invasive Alien species,” Convention on Biological Diversity, 2005, http://www.biodiv.org/programmes/cross-cuttings/Alien

D. S. Wilcove, D. Rothstein, J. Dubow, A. Phillips, and E. Losos, “Quantifying threats to imperiled species in the U. S.,” BioScience, vol. 48, no. 8, pp. 607–615, 1998.

A. E. Newsome and I. R. Noble, “Ecological and physiological characters of invading species,” in Ecology of Biological Invasions: An Australian Perspective, R. H. Groves and J. J. Burdon, Eds., pp. 1–20, Australian Academy of Sciences, Canberra, Australia, 1986.

M. Rejmánek, “What makes a species invasive?” in Plant Invasions: General Aspects and Special Problems, P. Pysek, K. Prach, M. Rejmánek, and M. Wade, Eds., pp. 3–13, SPB Academic, Amsterdam, The Netherlands, 1995.

M. Rejmánek, “Invasibility of plant communities,” in Biological Invasions: A Global Perspective, J. A. Drake, H. A. Mooney, F. di Castri et al., Eds., pp. 369–388, John Wiley & Sons, Chichester, UK, 1989.

D. M. Lodge, “Biological invasions: lessons for ecology,” Trends in Ecology and Evolution, vol. 8, no. 4, pp. 133–137, 1993.

R. J. Hobbs and L. F. Huenneke, “Disturbance, diversity, and invasion: implications for conservation,” Conservation Biology, vol. 6, no. 3, pp. 324–337, 1992.

J. A. McNeely, H. A. Mooney, L. E. Neville, P. Schei, and J. K. Waage, “A global strategy on invasive Alien species,” in Collaboration With the Global Invasive Species Programme, IUCN, Gland, Switzerland, 2001.

J. A. Drake, H. A. Mooney, F. di Castri et al., Biological Invasions: A Global Perspective, John Wiley & Sons, New York, NY, USA, 1989.

M. Williamson, Biological Invasions, Chapman & Hall, New York, NY, USA, 1996.

J. R. Carey, P. Moyle, M. Rejmánek, and G. Vermeij, “Invasion biology,” Biological Conservation, vol. 78, pp. 1–214, 1996.

P. Pysek, M. Chytry, J. Pergll, J. Sadloland, and J. Wild, “Plant invasions in the Czech Republic: current state, introduction dynamics, invasive species and invaded habitats,” Preslia, vol. 84, pp. 575–629, 2012.

D. M. Richardson, P. Pyšek, M. Rejmánek, M. G. Barbour, F. Dane Panetta, and C. J. West, “Naturalization and invasion of Alien plants: concepts and definitions,” Diversity and Distributions, vol. 6, no. 2, pp. 93–107, 2000.

P. Pyšek, J. Sádlo, and B. Mandák, “Catalogue of Alien plants of the Czech Republic,” Preslia, vol. 74, no. 2, pp. 97–186, 2002.

M. B. Raizada, “Recently introduced or otherwise imperfectly known plants from the upper gangetic plain,” Journal of Indian Botanical Society, vol. 14, pp. 339–348, 1935.

M. B. Raizada, “Recently introduced or otherwise imperfectly known plants from the upper gangetic plain,” Journal of Indian Botanical Society, vol. 15, pp. 149–167, 1936.

J. K. Maheshwari, “Studies on the naturalized Flora of India,” in Proceedings of the Summer School of Botany, pp. 156–170, New Delhi, India.

K. M. Matthew, “Alien flora of Kodai Kanal and Palni Hills,” Records of Botanical Survey of India, vol. 20, pp. 1–241, 1969.

G. Singh and B. Misri, “Some exotic ornamentals of Kashmir,” Indian Journal of Horticulture, vol. 31, p. 834, 1974.

G. Singh and P. Kachroo, “Exotic trees and shrubs of Kashmir,” Indian Forester, vol. 109, pp. 60–76, 1983.

J. K. Maheswari and S. R. Paul, “The Alien flora of Ranchi,” Journal of the Bombay Natural History Society, vol. 72, pp. 158–188, 1975.

P. K. Hajra and B. K. Das, “Vegetation of gangtok with special reference to Alien plants,” India Forums, vol. 107, pp. 554–566, 1982.

B. D. Sharma, Exotic Flora of Allahabad, Botanical Survey of India, Dehra Dun, India, 1984.

R. P. Pandey and P. J. Parmar, “The exotic flora of Rajasthan,” Journal of Economic and Taxonomic Botany, vol. 18, pp. 105–121, 1994.

S. R. Kshirsagar, “Origin, present status and distribution of exotic plants in South Gujarat,” Indian Journal of Forestry, vol. 28, pp. 136–143, 2005.

P. S. Negi and P. K. Hajra, “Alien flora of Doon Valley, Northwest Himalaya,” Current Science, vol. 92, no. 7, pp. 968–978, 2007.

H. A. Mooney and J. A. Drake, “The ecology of biological invasions,” Environment, vol. 29, no. 5, pp. 10–37, 1987.

C. M. D'Antonio and P. M. Vitousek, “Biological invasions by exotic grasses, the grass/fire cycle, and global change,” Annual Review of Ecology and Systematics, vol. 23, no. 1, pp. 63–87, 1992.

P. T. Jenkins, “Trade and exotic species introductions,” in Invasive Species and Biodiversity Management, O. T. Sandlund and P. Schei, Eds., pp. 229–235, Kluwer Academic, Dodrecht, The Netherlands, 1999.

H. A. Mooney and R. J. Hobbs, Invasive Species in a Changing World, Island Press, Washington, DC, USA, 2000.

C. S. Elton, The Ecology of Invasions by Animals and Plants, University of Chicago Press, Chicago, Ill, USA, 2000.

R. Cowie, “Does the Public care about Species loss? A Glimpse into the Public's thinking,” Conservation Biology in Practice, vol. 2, pp. 28–29, 2001.

E. Wasson, Complete Encyclopedia of Trees and Shrubs: Descriptions, Cultivation Requirements, Pruning, Planting, Thunder Bay Press, San Diego, Calif, USA, 2003.

C. S. Reddy, G. Bagyanarayana, K. N. Reddy, and V. S. Raju, “Invasive Alien Flora of India,” National Biological Information Infrastructure, USGS, USA, 2008, http://www.isws.in/invasive-plants-of-india.php

M. A. McGeoch, S. H. M. Butchart, D. Spear et al., “Global indicators of biological invasion: species numbers, biodiversity impact and policy responses,” Diversity and Distributions, vol. 16, no. 1, pp. 95–108, 2010.

A. S. Raghubanshi, L. C. Rai, J. P. Gaur, and J. S. Singh, “Invasive Alien species and biodiversity in India,” Current Science, vol. 88, no. 4, pp. 539–540, 2005.

Y. H. Sujay, H. N. Sattagi, and R. K. Patil, “Invasive Alien insects and their impact on agroecosystem,” Karnataka Journal of Agricultural Sciences, vol. 23, pp. 26–34, 2010.

P. Singh, “Lantana Weed and Lantana Lace bug,” Indian Forester, vol. 102, pp. 474–478, 1976.

P. M. Sinha, “Studies on the use of some Weedicides on Lantana camara,” Indian Forester, vol. 102, pp. 298–305, 1976.

V. B. Sawarker, “Lantana camara on wildlife habitats with special reference to the melaghat tiger reserve,” Cheetal, vol. 26, pp. 24–38, 1984.

K. P. Singh, A. N. Shukla, and J. S. Singh, “State-level inventory of invasive Alien plants, their source regions and use potential,” Current Science, vol. 99, no. 1, pp. 107–114, 2010.

C. S. Reddy, “Catalogue of invasive Alien flora of India,” Life Science Journal, vol. 5, no. 2, pp. 84–89, 2008.

K. C. Sekar, “Invasive Alien plants of Indian Himalayan region—diversity and implication,” American Journal of Plant Science, vol. 3, pp. 177–184, 2012.

S. H. Wu, C. F. Hsieh, and M. Rejmánek, “Catalogue of the naturalized flora of Taiwan,” Taiwania, vol. 49, pp. 16–31, 2004.

Q. Q. Huang, J. M. Wu, Y. Y. Bai, L. Zhou, and G. X. Wang, “Identifying the most noxious invasive plants in China: role of geographical origin, life form and means of introduction,” Biodiversity and Conservation, vol. 18, no. 2, pp. 305–316, 2009.

S. Tripathi and R. P. Shukla, “Effect of clipping and grazing on various vegetational parameters of grassland communities of Gorakhpur, Uttar Pradesh,” Tropical Ecology, vol. 48, no. 1, pp. 61–70, 2007.

K. S. Dogra, R. K. Kohli, and S. K. Sood, “An assessment and impact of three invasive species in the Sivalik Hills of Himanchal Pradesh, India,” International Journal of Biodiversity Conservation, vol. 1, pp. 4–10, 2009.

K. G. Saxena, “Biological invasion in the Indian sub-continent: review of invasion by plants,” in Ecology of Biological Invasion in the Tropics, P. S. Ramakrishnan, Ed., pp. 53–73, International Scientific Publications, New Delhi, India, 1991.

S. Tripathi, Plant diversity of grassland of north-eastern U.P. with emphasis on population of Parthenium hysterophorus L. [Ph.D. thesis], Gorakhpur University, Gorakhpur, India, 1999.

S. K. Sood, S. Kumar, K. S. Dogra, and R. Sharma, “Alien plants distribution and ecology in the temple-courtyards of Himachal Pradesh, North-West Himalaya,” Himachal Pradesh University Journal, pp. 1–11, 2011.

C. H. Chou, “Allelopathic researches in the subtropical vegetation in Taiwan,” Comparative Physiology and Ecology, vol. 5, pp. 222–234, 1980.

P. S. Ramakrishnan, Ecology of Biological Invasions in the Tropics, International Scientific, New Delhi, India, 1991.

K. G. Saxena and P. S. Ramakrishnan, “Partitioning of biomass and nutrients in the secondary successional herbaceous population subsequent to Slash and Burn,” Proceedings’of the Indian National Science Academy, vol. 8, pp. 807–818, 1982.