Invasive Alien Plants of Indian Himalayan Region — Diversity and Implication

The present study deals with comprehensive list of Invasive alien plants of Indian Himalayan Region with background information on family, habit and nativity. A total of 190 invasive alien species under 112 genera, belonging to 47 families have been recorded. Among these, the dicotyledons represent by 40 families, 95 genera and 170 species; monocotyledons represent by 7 families, 17 genera and 20 species. The analysis of invasive species reveals that 18 species have been introduced intentionally, while the remaining species established unintentionally through trade. In terms of nativity, amongst 13 geographic regions, the majority of invasive plants reported from American continent (73%). While in life form analysis, the herbs (148 species) are dominant, followed by shrubs (19 species), Grass (11 species), Trees (4 species), sedges and climber (3 species each). Most of the invasive species are annual habit (63%). Apart from these, 90 species (47%) are being used by locals for medicinal purposes. A better planning is needed for early detection to control and reporting of infestations of spread of new and naturalized weeds to be monitored.


Introduction
The Himalaya, is an enchantment territory of the nature where the magnificence of the world's highest mountains is mirrored in the rugged beauty and unique culture of the people who live in their shadow.The Indian part of Himalayas covering an area about 5 lakh km 2 (about 16.2% of country's total geographical area) and forms the northern boundary of the country.It extends between latitudes 26˚20' and 35˚40' North, and between longitudes 74˚50' and 95˚40' East.The Indian Himalayan Region (IHR) is spreading on 10 states (administrative regions) namely, Jammu & Kashmir, Himachal Pradesh, Uttaranchal, Sikkim, Arunachal Pradesh, Meghalaya, Nagaland, Manipur, Mizoram, Tripura, and hill regions of 2 states viz., Assam and West Bengal of Indian Republic.Starting from foot-hills in the south (Siwaliks) the region extends to Tibetan plateau in the north (trans-Himalaya) comprising about 95 districts of the country and contributes about 16.2% of India's total geographical area [1].The most of IHR area is covered by snow-clad peaks, glaciers of higher Himalaya, dense forest cover of mid-Himalaya.A total of 10,000 plant species are estimated in IHR, of which 3160 species are endemic [2].There is no record about the invasive species found in IHR.
Alien species are exotic organisms that occur outside their natural adapted ranges and dispersal potential [3].
Many alien species supports our farming and forestry systems in bulk.However, a few alien species become invasive when they are introduced intentionally or unintentionally outside from their natural habitats into new areas where they express the capability to establish, invade and out-compete native species [4,5].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 to native biological diversity.These invasive are widely distributed among all categories of living organisms as well as all kinds of ecosystems throughout the world.
Invasive species cause loss of biodiversity including species extinctions, changes in hydrology and ecosystem function [6].The exotic plant species vary from native one, based on their requirements, modes of resource acquisition and more consumption which may cause changes in soil structure, its profile, decomposition, nutrient content, moisture, etc.It results significant undesirable impacts on the biodiversity and ecosystems.Thus, Invasive species are a serious hindrance for conservation and sustainable use of biodiversity.Biological invasions now operated on global level and it will undergo rapid increase due to increasing globalization of markets, rise in global trade, travel and tourism [7].Therefore, it is very important to make an effective implication management of invasive species, knowledge about their diversity, life form, habitat, uses, is essential.Considering these reasons, the present study has been selected to enumerate the alien species of Indian Himalayan Region and its diversity with future implication of the region.
The nativity of the invasive plants was recorded from the published literature [22][23][24][25][26][27][28][29][30][31][32][33][34][35].The modes of introduction of these species in Indian Himalayan Region (IHR) were recorded from the published literature and categorized as food, fodder, medicinal, ornamental, etc. Plants were categorized by life form (herb, undershrub, shrub, climber and tree) and habit (annual and perennial).Habitat (wasteland, cultivated field, river banks, forest, roadside, aquatic, etc.) where a given species was most abundant also noted and parasitic plants were also recorded.Literature and herbarium were consulted to find out use value, if any, of these species.The invasive species are enumerated alphabetically in tabular form, followed by author's abbreviations, name of the Family, Nativity, Life form, Habit, Uses, Habitat and mode of Introduction.
A total of 13 different geographic regions in terms of nativity are recorded in the present study.Among these, about 90% are contributed by four major geographical regions, viz., continent of America (140 sp.), Africa (20 sp.), Europe (7 sp.) and Mediterranean (4 sp.).The American continents contributed majority (73%) of noxious invasive plants in IHR.The Africa and Europe contribute 10 and 3 percent respectively.Annuals comprise about 63% (120 sp.) and the remaining are perennials.Herbs constitute 77% (148 plants), whereas trees were represented by only four species viz., Acacia dealbata, A. farnesiana, Borassus flabellifer and Leucaena latisiliqua; three climbers namely, Antigonon leptopus and Merremia aegyptia, Solanum seaforthianum have been recorded apart from 19 Shrubs (Table 1 and Figure 1).Three sedges recorded as an invasive species namely, Cyperus difformis, C. iria and Fuirena ciliaris.Apart from these, 11 species of grasses are also recorded as an Invasive of IHR (Table 1).While analyzing the plant habit, 63% are annuals and 37% are perennials.The genera with the highest number of alien invasive species in IHR are Ipomoea (10 species); Cassia (9 sp.); Alternanthera, Corchorus and Solanum (5 sp.each); Cleome,    About 54% of invasive species were most abundant in wastelands, while cultivated fields, road sides, river beds, forest/forest edges were favored by 17%, 15%, 10% and 9% respectively.A search of literature, herbarium and consultation with local people indicated that several of the invasive species are also being used for different purposes for example, the stem of Malvastrum coromandelianum, Sesbania bispinosa, Sida acuta, and Cannabis sativa is being used for fibre, and Borassus flabellifer is being used for Hand-held fan.Ninety species listed in Table 1 are reported to be used by locals for medicinal purposes.The species namely, Leucaena leucocephala is being effectively used for social forestry.The uses of twenty seven species are not known or even not used by locals.Five plants are reported having high allelopathic potential, namely, Echinochloa crusgalli, Lagascea mollis, Lantana camara, Parthenium hysterophorus and Prosopis juliflora.
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 invasive 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 [3].In Indian Himalayan Region, comprehensive studies on invasive species and plant invasions are still missing.In view of this, the present study attempted to focus on document the invasive alien species in the flora of IHR.This listed invasive exotic species will serve as basic information for future research towards the conservation of endemic and natural forest vegetation of Himalaya.
In IHR, 190 species distributed in 112 genera and 47 families recorded as invasive alien in the flora.Amongst the recorded invasive species, many plants are known invasive of nearby region also.For example, 124 species listed in table 1 are common invasive in the state of Uttar Pradesh [35].Among these invasive species of IHR, 73% are native to American continent.The invasive flora of India also concerns more than 58% of invasive plants are native to American continent [34,35].The lesser percentage of American elements in IHR may be due to the presence of high altitudes, as the Europian flora contributed maximum percentage of invasive species in Kashmir Himalaya [37].Annuals are recorded the predomi-

Discussion
Alien species are non-native or exotic organisms that occur outside their natural adapted ranges and dispersal potential [6].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 [3].International Union for Conservation of Nature and nant invasive flora of IHR (63%), so the habit-wise classification of alien invasive shows a preponderance of herbs (77%).Further, greater viability and tolerance to harsh conditions could result this preponderance of herbs in the alien flora.Asteraceae is the dominant invasive family of IHR and contributed most of the exotic weed species in our country [34].Singh et al. [35] also recorded the dominance of Asteraceae in invasive alien flora of Uttar Pradesh and Rao and Murugan [37] also found that the Asteraceae is dominating family in alien flora of India.It is obvious that the family Fabaceae is one among the largest families of alien flora of IHR and having the potential of Nitrogen fixing capacity would be helpful to them in colonizing the empty niches.It is obviously recorded that 47 percent of the invasive species are under the consideration of medicinal purposes.But some of the species like Echinochloa crus-galli, Lagascea mollis, Lantana camara and Parthenium hysterophorus are having high allelopathic potential and harmful to natural plant population [35].
The 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, reproducetive biology, physiology and phytochemistry is essential [3].Monitoring of invasion can be done through qualitative approach like species inventory (seasonally) and quantitative approach using phytosociological methods and mapping using ground-based methods (via map overlays or GPS), remotely-sensed images (aerial photos, high resolution multi-spectral digital data).A better planning is needed for early detection and reporting of infestations of spread of new and naturalized weeds by creation of plant detection network in IHR by establishing communication links between taxonomists, ecologists and land managers to monitor and control.

Figure 2 .
Figure 2.Ten dominant families of invasive species.