Invasive plants have spread all over the world, including the Himalayan region. In 2009, the distribution pattern of invasive alien plants was studied on 38 plots, from 100 to 4200 m, in Arunachal Pradesh and Assam, India. Eighteen invasive alien plants (frequency >5%) from 7 families were recorded, of which 15 species (83.3%) were from North and South America. The most common plants by both frequency and coverage (>50%) were Ageratum conyzoides, Chromolaena odorata, and Mikania micrantha. Species composition changed with altitude. Thirteen species grew in the tropical zone, 10 in the subtropical, 6 in the temperate. and 1, Taraxacum officinale, in the subalpine zone. We suggest that low temperature and snowfall in the highlands may filter nonadapted species from tropical regions and that recent construction and use of roads facilitate the establishment of invasive alien plants. Although several invasive alien plants were regarded as noxious weeds, local residents in the study area mentioned their beneficial uses: A. conyzoides and Solanum carolinense are used as medicine, Galinsoga quadriradiata is used as a vegetable, and Eichhornia crassipes is used to improve fish growth in aquaculture. Information from scientific assessment and local perception of invasive alien plants will assist in the development of appropriate plant resource management plans in Arunachal Himalaya.
Many plant species have been either accidentally or deliberately translocated far from their native areas (Khuroo et al 2007). Newly introduced plants, called alien plants (Pysek et al 2004), have various effects on the environment and economy of non-native areas. Some alien species, often cultivated, may provide food, medicine, fuel, or fodder to local communities (Kull et al 2007; Roder et al 2007). Other alien species have negative impacts on agricultural production, forest regeneration, livestock grazing, native vegetation, and ecosystems or human health (Pimentel et al 2000; Sharma et al 2005; Kohli et al 2006). Introduced species with high reproductive rates and the potential to spread rapidly over large areas are regarded as invasive alien plants (Pysek et al 2004).
The Himalayan region has also been invaded by alien plants (Khuroo et al 2007). The vegetation of Arunachal Himalaya is known for its great diversity and endemism (Behera et al 2002; Hegde 2003; Bhagabati et al 2006), and many plants are used for food, medicine, resin, fiber, handicrafts, or cultural rituals (Tag and Das 2004; Tag et al 2008). There have been few studies of invasive alien plants in this region, and information is required for management planning.
Arevalo et al (2005) and Pickering and Hill (2007) report that road construction facilitated plant invasion in mountainous regions and that the distribution pattern of invasive plants along roadsides varied with altitude. Arevalo et al (2005) found the highest number of alien plants at intermediate altitudes between 0 and 2000 m. Pauchard and Alaback (2004) showed that alien species richness was negatively correlated with elevation along roadsides between 280 and 1290 m. Similar patterns of invasion after road construction and distribution with altitude may also apply to the Arunachal Himalaya region.
The present study compiled information on the distribution patterns of some invasive alien plants alongside roads in Arunachal Himalaya and gathered information on cultural perceptions of invasive plants for development of plant resource management.
Material and methods
Arunachal Pradesh (26°28′–29°31′N; 91°30′–97°30′E) and Assam (24°09′–27°58′N; 89°42′–96°01′E) are located at the eastern end of the Himalayan region at altitudes between 100 and 7000 m. There are 3 seasons per year: a warm and dry summer (March–May), monsoon (June–September), and a cool and dry winter (October–February). About 85% of annual rainfall (3000 mm) occurs during the monsoon season. Mean annual maximum and minimum temperatures are 29.3°C and 19.2°C in Itanagar (200 m), 27°C and 16°C in Along (300 m), 22°C and 12°C in Ziro (1600 m), and 19°C and 5°C in Tawang (3000 m), respectively (Purkayastha 2008).
Vegetation types vary with altitude and climatic conditions, from tropical (below 900 m), subtropical (900–1800 m), temperate (1800–3500 m) to subalpine and alpine (above 3500 m). Rice is cultivated below 2000 m on the plain and