Bamboo blooms in Odisha sanctuary, but rat boom and crop damage need not be a given

  • Bamboo clumps in Chandaka-Dampara Wildlife Sanctuary in Odisha are flowering, and this has triggered scare of a boom in rat population and subsequent crop loss.
  • A mass flowering phenomenon seen at long intervals in bamboo plants, known as gregarious bamboo flowering, is known to trigger rodent outbreaks and subsequent famine in northeast India.
  • The ‘mautam’ famine in Mizoram is associated with the flowering of the bamboo Melocanna baccifera, locally known as ‘mautak’. Besides Mizoram, regular rodent migration following gregarious bamboo flowering, fruiting and seeding also occur in Manipur, Arunachal Pradesh, Meghalaya, Tripura and Nagaland.
  • Even though increase in rat population, disease outbreak and crop loss need not happen in all locations, experts feel that there is a need to monitor the situation.

Around mid-December last year (2017), dense clumps of Indian thorny bamboo (Bambusa bambos), burst into flower simultaneously across several square km of the Chandaka-Dampara Wildlife Sanctuary, close to the Odisha state capital Bhubaneswar. 

This recent organised flowering event, technically known as ‘gregarious bamboo flowering’, has brought the spotlight on the so-called “botanical enigma” that is reported to have wreaked ecological havoc in rural corners of the country’s northeast.

Gregarious bamboo flowering refers to the phenomenon when all populations of a particular species flower roughly at the same time. The bamboo plants die after flowering and setting seeds.

Such synchronised flowering, sometimes at intervals as long as 50 to 120 years, may bring in its wake a swarm of rats, subsequent famine and loss of lives and livelihoods.

Boom and bust

“Gregarious flowering occurred in Chandaka in a cycle of 40 to 45 years in Daba bamboo [Indian thorny bamboo]. It started in the second week of December 2017. Mature seeds started falling on the forest floor during the third week of March this year,” Kedar Kumar Swain, divisional forest officer, Chandaka Wildlife Division, told Mongabay-India.

In Chandaka Dampara, which was notified as a sanctuary in 1988, Daba forms about 10 percent of vegetation of the nearly 200 square km-wide protected area.

Gregarious bamboo flowering at Chandaka Dampara Wildlife Sanctuary, Odisha. Photo by Special Arrangement

Regular rodent migration following flowering, subsequent fruiting and seeding, is a scientifically accepted phenomenon. It has been documented in the northeastern states of Mizoram, Manipur, Arunachal Pradesh, Meghalaya, Tripura and Nagaland, as well as in Laos, Japan, Madagascar and South America. After devouring the seeds, the rodents turn their attention to paddy and other crops and granaries, triggering famine and potential rodent-borne disease outbreaks beyond borders.

Allaying concerns over rodent migration and famine, Swain said so far, impacts of the rare occurrence on wildlife have been positive. Meanwhile, the forest department has launched a study to map the impact of the flowering on wildlife and their habitats. It is also being proactive in preventing forest fire and biotic interference to facilitate natural regeneration of the species.

“We have noticed a congregation of residential birds and insects at flowering sites. Common langur, Rhesus macaque and elephants are feeding on succulent flowers and seeds. Peafowl, red junglefowl, jungle babbler, bulbuls are among the birds that are flocking at these sites. So far, impact on wildlife is positive,” Swain stressed.

Environmentalist Biswajit Mohanty said that while rat migration is not a concern at the moment, the major worry is the lack of food for elephants that could lead to rise in man-elephant conflicts. “They may be forced to move to households and paddy fields.”

Steven Belmain, professor of ecology at the Natural Resources Institute, University of Greenwich, UK, who was involved in the study of the most recent event (2004 to 2011) that took place in the border area of Mizoram, Chittagong Hill Tracts of Bangladesh and Chin, Myanmar, said the phenomenon is actually well- understood now in scientific terms.

“It is often perceived as a ‘botanical enigma’ largely because local people don’t understand how bamboo can synchronise its flowering over large scales, said Belmain.

Should officials be worried?

When asked whether there is need for worry due to the gregarious flowering, Belmain said: “I would say it partly depends on the historical context.  If there have been problems in the past in the area, this is likely to be known by the communities living there.  If such communities have not had problems during previous masting (mass seeding) events, there is probably little reason to be concerned.”

Not all historical cases may be well understood, particularly if the cycle is more than 50 years, said Belmain, stressing that “there is the potential for disease outbreaks and other issues that may not be have been previously appreciated”.

Canopy formed by the Bamboo branches at the Periyar National Park and Wildlife Sanctuary, India. Photo by Anand/Wikimedia Commons

“The government should at least monitor the issue and be prepared for impacts, either caused by subsequent rodent outbreaks, or other ecological imbalances leading to disease transmission to crops, livestock or people,” he added. For example, bamboo outbreaks in Argentina are known to facilitate hantavirus outbreaks.

Bamboo flowering and crop loss

Gregarious bamboo flowering is notorious for causing famine in Mizoram and Arunachal Pradesh. A saying goes in the northeast states, “when bamboo flowers, death and destruction will follow.”

In Mizoram, which has about 31 percent of its geographical area under bamboo, the famine associated with the flowering of the bamboo species Melocanna baccifera (locally called ‘mautak’) is referred to as mautam or ‘bamboo death’.

Of the over twenty species of bamboo in the state, Melocanna baccifera is the dominant forest resource. It is a unique bamboo that produces the largest fruits among all bamboos. It flowers once every half a century, signalling death and destruction to the locals.

The mautak bamboo grows naturally in northeast India, as also in Nepal, Myanmar and Bangladesh and is cultivated in several gardens world over.

There are two major reasons for the fear surrounding mautam in Mizoram, observed Shyamal Biswas of the National Centre for Disease Control, Plague Surveillance Unit, Bengaluru.

“The bamboo clumps die after flowering after every 48 years and it takes a few years before bamboo plants produce seeds again, leaving the soil bare and exposed which is disastrous in mountainous regions. This would lead to food scarcity, since several animals depend on this plant,” Biswas said.

As the flowers bloom in synchronicity across vast swathes, hungry rats descend on them like a plague and feed on the flowers and seeds of the dying bamboo tree. Most outbreaks are usually due to rats (Rattus spp).

“Because of the high nutritive value of bamboo fruits, there is a spontaneous increase in rat population. In addition, there is a drop in cannibalism [among rats] due to the availability of plenty of food during bamboo flowering. This leads to a multiplication in rat numbers and they feed on agricultural crops in the fields and granaries, leading to famine,” Biswas told Mongabay-India.

The rats not only devastate the naturally regenerating seeds and seedlings, they also reduce the regeneration rate of bamboo.

Green gold

In India around 16 million hectares (160,000 square km) is estimated to be under bamboo.

As many as 125 indigenous and 11 exotic bamboo species are found in India. More than 50 percent of the bamboo species occur in eastern India including eight states in the northeast region.

Closely interwoven with the region’s economy and culture, bamboo, around 50 years ago, was the solution for everything: right from construction material to the blade for cutting the umbilical cord of a newborn baby and even food for survival.

Apart from Melocanna baccifera, Bambusa tulda also has a life cycle of 48 years. The two species do not flower together at the same time. Mautam famines were recorded in Mizoram in 1815, 1863, 1911, 1959 and 2007.

Bamboo fruits of Bambusa tulda species responsible for ‘thingtam’ famine in northeast India. Photo by Shyamal Biswas.

But MNV Prasad of the University of Hyderabad has a word of caution. Since most bamboo flowering events are unpredictable, there is not sufficient information available for species to state without any doubt that flowering at such long, fixed intervals is the norm for that species, Prasad stressed.

“Only for Melocanna baccifera there is reasonable evidence to suggest that the patterns observed are likely to be representative of the species,” he added.

Other factors affect rat numbers

In fact, a surge in rat numbers may vary depending on the nature of fruits.

Melocanna baccifera fruits are large and so they can support a large population of rats. Fruits of the Indian thorny bamboo (Bambusa bambos) on the other hand resemble barley grains and may not support a large rat population,” Biswas elaborated.

Belmain pointed out that the rodent numbers may still be low – this depends on where you are in the masting (mass seeding) cycle.  

“Normally the rodent population expansion is only noticed near the end of the cycle when the remaining seeds are germinating.  It should still be possible to find seeds that have been damaged by rodents, or gnawed on,” said Belmain.

The lack of rodents may also be due to the rodent species in the area not being able to exploit the bamboo seeds as a food resource, he said.

“And it may be because of the species of bamboo not being a very good food resource.  Without more information it is hard to explain what is or is not driving rodent numbers in this case,” he added.

Gregarious bamboo flowering and rodent migration in Mizoram. Photo by Shyamal Biswas.

Biswas suggested that rodent management strategies that have been tested in northeast region and found effective by the scientists of national rodent management network can be applied since outbreaks continue to occur during or after the bamboo flowering.

“Rodent migration after gregarious bamboo flowering can trigger a consequence far more serious than crop destruction — an increase in the frequency of transmission of rodent-borne pathogens to human and animals,” Biswas added.

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