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Lantana likes living next to streams

  • Lantana covering a hillside in Bandipur National Park. Photograph by Raman Sukumar.

Lantana covering a hillside in Bandipur National Park. Photograph by Raman Sukumar.

Lantana is an alien invasive plant species that was introduced in India about 200 years ago. Finding ways to control its proliferation is still a challenge for both scientists and forest managers. A recent study has shone light on the conditions under which lantana proliferates.

Lantana camara L,(or simply lantana) is a woody shrub originally from South and Central America. European explorers brought it to Europe and cultivated it as an ornamental garden plant. It then spread to European colonies in other continents, soon to become an infamous weed. Today, it can be found in about 50 countries, and is known to be one of the most invasive species on earth.

In a paper to be published in the Journal of Biosciences, researchers from the Indian Institute of Science (details at the end) explain how lantana responds to different ecological challenges in the tropical dry forests of Mudumalai Tiger Reserve in Tamil Nadu.

Lantana has all the characteristics of an invasive plant. It does not have many predators or parasites that depend on the plant. It produces large quantities of fruit; animals and birds that eat them disperse the seeds to far off places. The species also alters ecosystem processes and has been shown to have an undesirable influence on the survival of the native species.

In Mudumalai Tiger Reserve, as in many other nearby forests such as Bandipur and Biligirirangaswamy Temple Tiger Reserves, it has not only flourished, but refuses to go.

Lantana is usually a scrambling bush, with an umbrella-like canopy and multiple stems at the base. Such bushes can grow up to 3m tall, with a diameter of up to 2m. In some parts of Mudumalai, lantana is a voracious climber on trees, reaching 10-15m into the canopy.

In ecological parlance, ‘edge’ denotes an area where two different habitats come into contact. In this study, the authors have called the bank of a stream or any water source an ‘edge’. Such regions are known to have better access to resources, often due to flooding, and hence are prone to invasion by a variety of species. These invaders consume the local resources, and flourish, often at the cost of species that are local to the region.

Invasive species respond in different ways to changes in an ecosystem. Hence, in order manage them, it is imperative to clearly understand their responses. Though the  invasion of the banks of  perennial rivers are well studied, their seasonal river counterparts are poorly understood. The present paper from the IISc researchers fills this gap to some extent.

Lantana growing in the tropical dry forests of Mudumalai could be influenced by four  major factors in their surroundings: distance from streams, amount of rainfall, availability of light, and the history of fire occurrences in the region. The researchers report how lantana responds to these challenges.

Spread across 321 sq km (which is less than half the area of Bangalore City), Mudumalai is home to a variety of habitats. The eastern parts of the sanctuary receives about 700 mm of rainfall annually (on an average, Bangalore receives 974 mm every year), and contains tropical dry thorn forests. The rainfall increases considerably as one moves from east to west. The wetter regions are home to semi-evergreen forests.

The researchers studied lantana proliferation across Mudumalai. Mudumalai is dotted with a number seasonal streams, and has a history of ground fires in the dry seasons. They measured the area covered by lantana at sixty locations, all near streams, and measured local conditions like shade and fire history as well. Lantana abundance (number of stems per unit area) and lantana area (area covered by the plant) were chosen as measures of proliferation.

The results show that Lantana loves to be close to the stream: both abundance and area covered was maximum near streams. They were also higher in areas which had  experienced fewer fires in the past 11 years. Lantana did not seem to get affected by shading by large trees. 

Managing and controlling the spread of invasive species in general, and lantana in particular, has been a problem. “Other researchers have reported a series of methods to control the spread of lantana: uprooting, cutting-and-burning, cutting rootstock, chemical and biological methods; but they found these methods fail to different extents to control its spread”, said Geetha.

“In Mudumalai, the most popular way of managing lantana is uprooting it. However, uprooting often causes buried seeds to come to the surface, starting a second bout of lantana spread in the managed area”, she continued. 

She says her study does not directly help devising plans to manage lantana. “However, forest managers can make decisions on where to manage lantana given that it is likely to be denser in certain areas”, said Geetha while explaining the significance of her findings.

Author information:

Geetha Ramaswami finished her PhD with Professor Raman Sukumar at the Centre for Ecological Sciences, Indian Institute of Science, Bangalore. She is available at geetha.ramaswami@gmail.com

Professor Sukumar: http://rsukumar.weebly.com/prof-r-sukumar.html