Details of this species in Shivalik Ranges
Source: Dogra et al. 2009
Species Notes for this Location:
Ageratum conyzoïdes forms monocultural or monospecific stands in the Shivalik Ranges of the north-western Himalayas in the province of Himachal Pradesh (Singh et al. Undated A). The weed is established dominantly in the area to an altitude of up to 1800 meters (Kohli et al. 2006, in Dogra et al. 2009). Singh (Undated) found that A. conyzoides was more dominant at the altitude range of 300 meters to 1500 meters than at 1500 meters to 2400 meters. The weed has spread extensively in this region, occupying the following habitats (Kohli et al. 2004; Singh et al. Undated; Dogra et al. 2009; Batish 2008): Forests; Grasslands; Plantations (eg: Pinus roxburghii); Agricultural fields; Horticultural land; Wastelands; Roadsides; Pastures; and Water channels. In general the favored niches of invasive plants in the Shiwaliks are: Open eroded areas; Deforested areas; Overgrazed grassland; and Fallow agricultural areas.
A. conyzoides flowers from July to March in India (Batish 2008). Its seeds are easily dispersed into wide areas in the hilly tracts of Shivalik hills by wind and water, which help in their establishment in a wide range of climatic conditions (Kohli et al. 2006, in Dogra et al. 2009). Reasons for the proliferation and invasiveness of the weed include: enormous seed production, high regeneration potential, fast growth rate, greater tolerance to conditions compared with other species and allelopathic interference (Callaway & Aschehoug, 2003, in Singh et al. Undated A; Singh et al. Undated A).
It should be noted that along with Ageratum conyzoides, the following plant weed species are highly established invasive plant species in the Shivalik hills: Lantana camara, Parthenium hysterophorus, Ricinus communis, Eupatorium odoratum (Chromolaema odorata), Artemisia scoparia, Datura stramonium, Chenopodium ambrosioides, Cassia occidentalis and Bidens pilosa. During a survey (2002 - 2004) of the lower Shivalik hills: A. conyzoides, P. hysterophorus and L. camara from subtropical America were found to be highly dominant in the Shivalik hills. These species directly affect ecosystem dynamics in the invaded habitats in lower Shivaliks (Kohli et al., 2004, in Dogra, Kohli & Sood 2009) and pose a threat to the establishment of other plant species (Kohli et al., 2004, in Dogra, Kohli & Sood 2009).
Management Notes for this Location:
Research: Work by Dogra and colleagues (2009) was carried out to find the intensity of invasion (dominance, density, abundance, frequency and importance value index) of these three significantly invasive species (A. conyzoides, L. camara, P. hysterophorus) in the lower Shivalik hills and to understand the impact of invasive plants on the structure and composition of other species. Their results showed that more than 20% vegetational area in lower Shivalik hills is covered by these three invasive species. The authors also found that the number of plant species is highly reduced in the areas invaded by these weeds and that the decrease was 30% for A. conyzoides. Similarly, Margalef index of species richness was also decreased by 36%. The index of dominance increased by 53% in the Ageratum invaded areas. The higher value of this dominance index among the invaded plant communities predicts the homogenous nature of the vegetation. The a-diversity of vegetation was drastically reduced due to the invasion of these three plant species in Shivalik hills (40% for Ageratum) Likewise, the number of abundant species (N1) and very abundant species (N2) and index of evenness were also significantly decreased in the areas invaded by these three invasive plant species. The comparison of the fresh and dry biomass of vegetation between the invaded and un-invaded areas also shows the decrease in productivity of communities in the invasive invaded areas.
Medicinal plants, including Acyranthes aspera, Dichanthium annulatum, Murraya koenigii, Adhatoda vasica, Carissa spp. and Colebrookea spp., declined in areas invaded by A. conyzoides (Singh Undated). There is an urgent need for the management of indigenous or medicinally valuable plants in the invaded areas under their natural habitats (Dogra et al. 2009).
Factors considered to contribute to the invasiveness of A. conyzoides are (Singh Undated): Fast growth rate; Unpalatable or bitter tasting - rich chemistry; Long flowering and fruiting periods; Very high seed production; Adaptability and wide ecological amplitude; High regenerative potential; and Absence of natural enemies / competitors.
The Shivalik Ranges in the North-western Himalayas in India are well-known for their rich floral diversity and the Himalayas as an entity constitute an important biodiversity hotspot (Batish 2008). During the last two decades humans have intentionally and unintentionally introduced a number of exotic weeds into the Himalayas; these weeds have invaded the area damaging the structure and dynamics of natural communities causing severe harm to its floral diversity (Batish 2008). The flora of the Shivalik Ranges is under threat due to the rapid invasion of invasive species (Dogra et al 2009).
Agricultural: The weed is a problem for farmers, ecologists, locals, environmentalists and animals (Batish 2008). It is a troublesome weed of cultivated lands. A. conyzoides is responsible for replacing grasses in pastures and causing fodder loss (as cattle do not feed on the weed), deteriorating soil quality and reducing crop quality and yield (wheat, chickpea, rice, maize, and sugarcane) (Singh Undated). A. conyzoides also adversely affects animal health; and causes hindrances to ploughing (Batish 2008).
Competition: A. conyzoides replaces other vegetation including native grasses (Batish 2008; Singh Undated).
Ecosystem change: Dogra and colleagues (2009) evaluated the impact of A. conyzoides on the diversity and floristic compositions of native species. It was found that as compared to control, in the Ageratum invaded area:
It was concluded that invasion by A. conyzoides drastically affects the productivity, composition and diversity of the invaded areas in Shivalik hills of Hamirpur district.
- The average number of plant species was reduced by 32% (81 species in the control area as compared to 55 in Ageratum invaded areas);
- Margalef's index of species richness, alpha species diversity and evenness index were reduced by 37%, 41% and 15%, respectively;
- The fresh and dry biomass of plants was significantly reduced by 52% and 48%, respectively ;
- The number of abundant species (N1) and very abundant species (N2) were also significantly reduced; and
- The value of index of dominance was higher, indicating that communities were homogenous in nature and dominated by a single species (compared with un-invaded communities which showed more heterogeneity).
Habitat alteration: The invasion of these three invasive plant species (A. conyzoides, L. camara, P. hysterophorus) highly reduces the available habitats or niches for the growth of other useful plant species. They are responsible for the loss of productivity and diversity of species in the invaded areas. They drastically alter the structure, function and dynamics of invaded habitats (Dogra, Kohli & Sood 2009).
Human health: A. conyzoides presents a health hazard to humans (Batish 2008).
Modification of hydrology: A. conyzoides chokes water channels (Singh Undated).
Modification of nutrient regime: A. conyzoides deteriorates soil quality (Batish 2008). The weed is strongly allelopathic and adversely affects crop productivity through its allelochemicals. Almost all parts of the weed (stem, roots, leaves, inflorescence), are known to cause allelopathic effects. Volatile allelochemicals include Precocene I, Precocene II and Caryophyllene etc. Non-volatile phenolic acids include gallic acid, coumalic acid, and protocatechuic acid, p-hydroxybenzoic acid, p-coumaric acid, sinapic acid and benzoic acid.
Dogra and colleagues (2009) found that the amount of phenolics in the soil was 41% higher in A. conyzoides-invaded areas than in control areas. The pH in the A. conyzoides-invaded areas was slightly higher than in the control areas. The conductivity of the ions was 31% more in the A. conyzoides invaded area as compared to control. Percent organic carbon and organic matter also increased in the invaded area by nearly 49%. The increase in the available nitrogen content was highest among all other nutrients. It increased by 57% in the invaded area. The amount of available phosphorus, potassium and sodium were more by 48%, 38% and 25% respectively in the A. conyzoides-invaded soil as compared to the control soil. The amount of available calcium, magnesium and chloride were more by 37%, 32% and 33% respectively in the A. conyzoides-invaded soil as compared to the control soil (Dogra et al 2009).
Reduction in native biodiversity: Dogra and colleagues (2009) found that A. conyzoides, L. camara and P. hysterophorus reduce species diversity and composition in the Shivaliks. The decrease in diversity indices and biomass in the invaded sites show that plant communities become less productive in response to these invasive plant species in the lower Shivaliks of Himachal Pradesh, India (Dogra et al. 2009). Batish (2008) found that A. conyzoides adversely affects biodiversity and checks the growth of grasses and other weeds. A. conyzoides can result in an up to 50% decrease in average dry biomass (grams per meter squared) and can cause an over 30% reduction in total species number (Batish 2008). Singh and colleagues (Undated) found that, compared with controls, native vegetation in A. conyzoides-infested habitats was significantly reduced (including numbers of species, plant density and biomass) especially in wastelands and grassland, indicating that invasion by A. conyzoides reduces plant biodiversity.
Dogra and colleagues (2009) found that the number of herbs decreased sharply (as compared to other life forms) in the A. conyzoides-invaded areas. Results showed that herbal vegetation was affected maximally as compared to other vegetation types. Major medicinal plants affected by the invasion of A. conyzoides were Murraya koenigii, Dichanthium annulatum, Cynodon dactylon, Trifolium repens, Achyranthes aspera, Adhatoda vasica and Carissa carandas (Dogra et al. 2009).
Last Modified: 27/11/2009 12:09:43 p.m.