Alien plants invasion in Horton Plains

Dr. Lalith GUNASEKERA
Invasive Plants Specialist - Melbourne, Australia

Spreading across over 3,169 hectares of land, Horton Plains had been originally known as Mahaeliya and had been known as ‘Elk Plain’ during the colonial period. Horton Plains situated at 2,100 metres above sea level, is nestled in the highest tableland of Sri Lanka in the Southern end of the central mountain.

Horton Plains consist of four ecosystems such as Montane evergreen forests, grasslands, marshy lands and aquatic ecosystem. On July 30, 2010, the central highlands of Sri Lanka which incorporates Horton Plains National Park was inscribed on the World Heritage list. As we all know, Horton Plains is one of our treasures given by nature. It has a large number of endemic flora and fauna species you won’t find anywhere in the world.

My recent visit to Sri Lanka in August 2011 allowed me to walk through this beautiful piece of land as I like to see the natural beauties of my motherland. As an invasive plant specialist I have the knowledge and skills to recognize most invasive plants of tropical/subtropical and temperate environments. Thus I always go searching around the environment for exotic plant species. There were a very few invasive plants recorded from the Horton Plains in the last century or so.

Gorse or katu-gas - Ulex europeus

The British were introduced this plant through the Royal Botanical gardens at Peradeniya in 1888 and then planted in their gardens in Nuwara Eliya area. It escaped from gardens and migrated to Horton Plains. There are no records found as to how it came to Horton Plains. Some believe that it was initially planted in Far Inn by the British owner and then escaped to Horton Plains. Anyhow this plant is still growing in the plains.

There are three more plant species introduced to Horton Plains during the colonial period. They are still growing in the grassland areas. Examples are:

Waralla - Pteridium aqulinium
Nil mal - Aristea ecklonii
Kikuyu grass - Pennisetum clandestinum

But I couldn’t believe my eyes after seen some of the worst invasive plant species along the walking track of Horton Plains as they were never recorded before.

Mist Flower - Ageratina riparia

This plant introduced to Sri Lanka through Hakgala Botanical garden in 1905 and used as a hedge plant in home gardens in up country home gardens. The plant has been spreading along the walking track towards to world’s end viewing area.

A native plant of Central and South America, Mist flower is a low growing sprawling perennial herb grow up to 40-60 cm tall. It produces numerous branching stems that produce roots at the joints where they touch the ground. Leaves are opposite, mostly 5-8 cm long and 2-4 cm wide, toothed along the edges and tapered at each end.

White small flowers produced at the ends of the branches. Large numbers of black seeds produced with fine white hairs at the tip. Mature plants can produce up to 100,000 seeds each year. They spread by wind, water animals and humans.

The Mist flower is an aggressive invader spreading into endemic forest areas and grasslands of Horton Plains and displacing native vegetation. It can quickly invade disturbed areas on mountain slopes and dominate riverine groundcover habitats excluding many native species and the native animals which were reliant upon those plants. This species is the most invaded invasive plant in Horton Plains. The Mist flower has been listed as a potential invasive plant under the provisional list prepared by the panel of experts on invasive species in Sri Lanka.

Suddha (Austroeupatorium inulifolium)

When I walked along the track, I was amazed to notice this species within Horton Plains as it has large buffer zone to protect the area from different invasions (humans, flora and fauna). There were several large Suddha plants are being grown in the Park and they are about two-three years old according to their appearance and growth.

This plant is similar in appearance to Podisinghomaran (Chromolaena odorata) and belongs to the same plant family Asteraceae but grows on higher elevations. The Suddha plant is a perennial, spreading scrambling shrub grows up to two-five meters tall. Stems covered with dense short hairs and moderately branched. Leaves are simple and opposite below becoming sub opposite or alternate above. Leaf petiole is one-two cm long, leaf blades are ovate to narrowly oblong, 7-14 cm long, two-eight cm wide, margins are serrate, three veined starting from well above base, hairy, pale green beneath. Flowers are terminal or arising from upper nodes. Flower head comprising three-four series of bracts enclosing 10-15 creamy white florets with corollas four-five mm long, flowers fragrant. Seeds oblong with a whitish pappus four mm long. Seeds are spread by wind, water, animals, humans and vehicles.

Suddha plant rapidly colonizes areas cleared for planting, open areas, waste lands, roadsides, natural forests, grasslands, wetlands, and riparian areas. This is a prohibited plant in Australia and listed as an ‘environmental weed’ and agricultural weed in the Global Compodium of Weeds. It is a serious weed in the Phillippines where it forms around thickets in rubber, tea and rosella plantations, upland rice and secondary forests.

According to my observation in Horton Plains, Suddha plants can be eradicated as it has not totally out of control. I assumed about 100-150 plants in total around the walking track. This is very important time to eradicate them before it get established in the park and displace native forest and grasslands.

Suddha plant has been listed as a potential invasive plant under the provisional list prepared by the panel of experts on invasive species in Sri Lanka.

Crofton Weed or Mexican Devil (Eupatorium adenophorum)

Once I observed a beautiful scene at World’s End, where I walked towards on Chimney Pool area. I passed several Suddha plants and suddenly noticed another aggressive invader in the same Asteraceae family named Crofton Weed. I wonder how this plant came into this isolated park. It is a puzzle. But I saw few small infestations of crofton weed around Nuwara Eliya area.

Crofton weed is native to Mexico presently serious weed in Australia, New Zealand, India, Thailand, Jamica, Fiji, South Africa, China and United States.

Crofton weed is a shrubby perennial with a woody rootstock and numerous upright stems. It usually grows 1-2 metres tall. Young drooping stems are soft and establish roots where they touch the ground. The leaves are bright green, diamond shaped, 50-70 mm long, 25-50 mm broad with the edges toothed and arranged in opposite pairs along the stem. Stems are usually purple and are covered stalked sticky hairs.

Stem branch in opposite pairs. Flowers are white, in small, dense heads at the ends of the branches. Seeds are slender, 2 mm long, almost black with fine white hairs at the tip. Mature crofton weed plant can produce between 10,000 and 100,000 seeds per year. Seeds very light (25,000 seeds/g) are highly viable and disperse by wind, water, animals and humans.

Crofton weed densely overtopping ground covers and preventing native plant species from regenerating. It can invade a wide range of habitats and are especially happy in wetland areas where they compete with vulnerable native plant species. This plant can tolerate shade, damp areas and moist soil types.

This plant should be included in the invasive plants list in Sri Lanka.

Further I noticed that there are some more new and emerging invasive plants such as wild tobacco, banana passion, Mexican Elder etc in the buffer zone area out of the Horton Plains. It is very important to keep an eye on this important land mass to keep them away. Please protect this place from alien invasive plants. Then future generations will appreciate us for our hard work.

I am always happy to help protect our unique environment of Sri Lanka. If you have any question or help, don’t hesitate to contact me on my email. [email protected]