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INVASIVE ALIEN SPECIES


FLORA

For a small island, Sri Lanka is rich in biological diversity. Yet, this natural wealth is under threat from various sources, including invasive alien species. IAS grow rapidly, compete vigorously, push out native species and alter ecosystems. Their impacts are enormous and they have the potential to cause damage to the environment, human health, livelihoods and the economy.
 
 
 
 

Lantana

(Lantana camara)

Family: Verbenaceae

Common name: Lantana, Big sage, Wild sage (English), Gandapana, Baloliya, Rata Hinguru (Sinhala).

Synonyms: Lantana mutabilis , Lantana scabrida , Lantana viburnoideslLantana camara

Taxonomic notes:

The variety hybridizes readily with other varieties and other related species when these grow in proximity, so intermediate and puzzling forms are very common.

Character identification:

Lantana camara is a low, erect or subscandent, vigorous shrub which can grow to 2-4 m in height. The leaf is ovate or ovate oblong, 2-10 cm long and 2-6 cm wide, arranged in opposite pairs. Leaves are bright green, rough, finely hairy, with serrate margins and emit a pungent odour when crushed. The stem in cultivated varieties is often non- thorny and in weedy varieties has re-curved prickles. It is woody, square in cross section, hairy when young, cylindrical and up to 15 cm thick as it grows older. Lantana is able to climb to 15 m with the support of other vegetation. Flower heads contain 20-40 flowers; the colour varies from white, cream or yellow to orange pink, purple and red. The fruit is a greenish blue-black colour, 5-7 mm in diameter, drupaceous, shining, with two nutlets.

Total length: Can grow to 2-4 m in height. Up to 15 m with support of other vegetation

Morphologically similar species:

Sri Lanka has another three species (L. trifolia, L. montevidensis, and L. indica) of Lantana which were introduced to the island during the colonial period, but have very limited distribution. There are few varieties of this species in Sri Lanka, however, the variety that is commonly identified as invasive is L. camara var. aculeata.

History and introduction:

The species is native to South America and it is believe that this species was introduced to Sri Lanka around 1826 through the Royal Botanic Gardens. However, the history of introduction of L. camara to Sri Lanka is not confirmed due to the absence of proper documentation records. It has been cultivated for over 300 years and now has hundred of cultivars and hybrids.

Present distribution:

Naturalized in approximately 60 countries or island groups. Occurs widely in the Asia-Pacific region, Australia, New Zealand, Central and South America, West Indies and Africa.

It is a major invasive species found throughout Sri Lanka and has invaded natural ecosystems particularly when open conditions are prevalent. This species is commonly found in dense stands along roadsides and abandoned lands.

It has invaded Udawalawe National Park, a leading elephant sanctuary of the island, significantly reducing the grazing lands available for elephants. It has also spread in forest plantations and degraded natural forests interfering with natural regeneration (Weerawardane, 2000).

Dispersal and reproduction (pollination and seed dispersal):

Mature plants produce up to 12,000 seeds annually. Seed germination occurs when sufficient moisture is present; germination is reduced by low light conditions. Fruit dispersal is through frugivorous birds, jackals and rodents. Viability of its seeds is improved when the seed passes through the digestive system of birds and animals. High light intensity and soil temperature will stimulate germination of seeds which means that clearing of forest areas, inappropriate burning and other disturbances will help spread the weed. Seeds are capable of surviving the hottest fires (FAO).

Impact on native species and habitats:

It infests diverse habitats with various soil types. Affected areas in Sri Lanka include national parks and elephant pastures. The plants can grow individually in clumps or as dense thickets, crowding out more desirable species. In disturbed native forests it can become the dominant understorey species, disrupting succession and decreasing biodiversity.

Direct exploitation / destruction of native species:

As the density of lantana in forests increases, species richness decreases (Fensham et al., 1994, in Day et al., 2003). Its allelopathic qualities can reduce vigour of plant species nearby and reduce productivity in orchards (Holm et al., 1991, in Day et al., 2003). According to studies, it shows allelopathy where it can suppress the growth of the plants. Phenotypic plasticity (ability to change morphology to suite environmental conditions) helps L. camara to thrive in various environmental condions while native species struggle to survive.

Current uses:

Lantana camara is mostly used as a herbal medicine and sometimes as firewood and mulch. Lantana berries are consumed as fruit by children. It is also a butterfly attracting plant. Stem of the plant is also used in handicrafts.

Natural threats (pest / predators):

Not known. Leaves of this plant is toxic to many animals.

Prevention and control:

Preventing the spread of Lantana is the most cost-effective management tool. This would require the restriction of further importation of Lantana into the country, restriction of sale and use of Lantana in gardens as well as strategically controlling infestations wherever they currently occur. Mechanical control: Stick-raking, bulldozing, ploughing and grubbing (medium sized plants) are the main methods of control. Hand cutting using brush cutters, hand pulling, chain pulling and flame weeding are also used. Re-growth will be imminent if the rootstock is not removed while weeding. However, mechanical control is suitable only for small areas and is not recommended in areas susceptible to erosion. Fire can provide some control when used under the right conditions, especially if the fires are hot and Lantana is actively growing. But, when using fire as a management tool, the risk to people and property must be avoided. Burning is not recommended in natural forest areas and vine thickets for various reasons. Re-vegetation of a treated site by planting trees or encouraging naturally occurring seedlings is a key component of a Lantana management program. Biological control, in itself, has not been effective in controlling Lantana infestation wherever it has been attempted, the main reasons being the extreme variability of the plants, the extensive climatic range it invades and the high level of parasitism on the natural enemies.

Special notes:

L. camara is a highly variable species. Cultivars can be distinguished morphologically (variation in flower size, shape and colour; leaf size, hairiness and colour; stem thorniness), physiologically (variation in growth rates, toxicity to livestock) and by chromosome number and DNA content (Binggeli, 1999).

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ias lantana map

 
 
IAS Documentary
Information for the public knowledge about Invasive Alien Species in Sri Lanka...

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Information about the policies of Invasive Alien Species in Sri Lanka...



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