Written by Chaitanya Krishna, photographs by Sarang Mhamane and Wikimedia Commons

In the past, people feared invasions by neighbouring kingdoms, because apart from the very real threat to life and limb, their culture and way of life could be lost to the invaders. A far cry from the invading armies of yester year, today’s invasions are aided by more commonplace means such as world wide commerce and tourism. The raiders of today’s ark are certain plants and animals who have travelled, often as hitchhikers to new territories and in the process affected the native or original flora and fauna of a region. Research on modern day invasions suggest that fast growing rapidly reproducing species capable of adapting quickly to new environmental conditions can become invasive when introduced into new areas. There are some invasive species that have received a lot of attention due to their potential to create great economic losses (e.g. Zebra mussels in North America) and others have had ecological impacts (e.g. Lantana camara). One study estimated the environmental damages and losses caused by invading alien species in the United States to be $120 billion/year. The plant Hyptis suaveolens, commonly called pignut or chan, has remained in the background, but is starting to show symptoms of becoming invasive in India.

The Hyptis invasion

Native to tropical America, Hyptis was introduced widely across the world and is now found in tropical Africa, Asia and Australia. In India, Sir Joseph Dalton Hooker, the British botanist recorded Hyptis in the late 19th century from the Deccan and Cachar regions, but the species was not recorded from north India. Around the same time, John Firminger Duthie, an English botanist and explorer, did not record Hyptis in the Upper Gangetic Plain, a vast area bounded by the Himalayan foothills to the north and the Vindhyan mountain range in the south. Now, a century later, researchers have found that certain areas of the Vindhyan plateau have been invaded by Hyptis. In the Himalayan foothills, the species was reported by the mid 1970s itself. A recent study in the Doon Valley and Siwalik foothills has estimated that up to 11 square kilometres has been invaded by Hyptis, primarily along riverine areas, forest edges and open areas. This sequence of events clearly suggests that the plant is spreading across India.

Below, Hyptis plants in the grassland areas of the Great Indian Bustard Sanctuary at Nannaj in Maharashtra.

Laying waste to native biodiversity

Hyptis reportedly establishes in many different kinds of areas; alongside roads, railway tracks, forest clearings and areas typified by rocky and arid substrates. Several traits of Hyptis enable it to spread. It produces a large number of seeds which bear hooks, which enable the seeds to be transported from one area to another by attaching themselves to the fur of passing animals or clothes of humans and the plants can tolerate dry periods. Additionally, the plant contains chemicals which inhibit the growth of native species, as demonstrated in the Vindhyan plateau, where it alters the composition of native plant diversity, and the plant itself is unpalatable to livestock. So if Hyptis is allowed to spread unchecked, the diverse set of native plant species edible to livestock will be replaced by an unpalatable weedy monoculture.

Detection and control

Hyptis may join the ranks of other invasive plant species like lantana and parthenium and have negative effects on native biodiversity if steps are not taken in earnest to control its spread. As in any attempts to control invasive plants, the best approach is early detection and removal as a means to prevent large areas from being affected. The best and most cost-effective method to control its spread is physically uprooting the plants before they have set seed, which occurs after the monsoon. Scientists at the Kerala Forest Research Institute have classified Hyptis as an invasive plant that poses medium risk to native flora. More such assessments are needed.

Today’s invasive species are a far cry from historical invaders. In the past, kingdoms went to great lengths to keep invaders at bay, the Great Wall of China is one such attempt. Unfortunately, even an architectural feat such as that will be unable to keep today’s invaders in check. Strictly enforced regulations at customs and border checkpoints will help, but in today’s era of globalization, the risk of species being transported to new regions in the world is ever present.

Controlling Hyptis: A case study

During post monsoon field work in 2009 in the Great Indian Bustard Sanctuary located near the village of Nannaj in Maharashtra, my field assistant and I stumbled across a plant that gave off a distinctive odour and looked vaguely familiar. “Raan Tulas” my field assistant replied in Marathi when I asked him if he knew the plant. The literal English translation being “Wild Tulsi”, the plant was Hyptis suaveolens.

Hyptis could proliferate and invade the semi-arid grasslands of the sanctuary, which are home to great Indian bustards, blackbuck, Indian wolves, Indian foxes and migratory pallid harriers. The resulting loss of the grassland habitat could affect almost all of the above species but of special concern is the threat to the great Indian bustard, a critically endangered iconic and majestic bird whose global population in the wild is estimated to be just 200 individuals.

Following the detection of Hyptis in 2009 in the sanctuary, the protected area manager was informed and a decision was taken to uproot the plants after the monsoon. Following the monsoon in 2010 and 2011, the Maharashtra Forest Department staff, interested youth from surrounding areas, the author and his research team joined hands to remove Hyptis from the sanctuary. In both years, the plants were uprooted by hand. This activity has controlled the spread of Hyptis in the sanctuary and needs to be continued in order to eventually eradicate the weed from the sanctuary.

Below: Maharashtra Forest Department staff, the author and his team after uprooting the Hyptis plants at the Great Indian Bustard Sanctuary at Nannaj in Maharashtra.

An edited version of this article appeared in the 30th June 2013 edition of the environmental magazine Down to Earth and can be accessed here.