FLOWERING

Bamboo Flowering at Anamalai Tiger ReserveThe flowering of bamboo can occur at many levels. On the smallest level, a single branch on a single culm of a single plant may produce a spikelet of flowers. At the largest level, an entire population, covering thousands of square kilometres, may flower and die in unision. Individual culms may flower and die while the parent plant remains unscathed, or whole plants may flower but survive to regenerate from rhizomes depending on the species. Mass flowering attracts the most attention, such as that of Bashania fangiana in the 1980s that affected the Giant panda, and the regular, once-every-48-year, flowering of Melocanna baccifera in Northeast India that brings famine and environmental degradation.

In many cultures the flowering of bamboos is strongly associated with the onset of natural disasters or famines. While evidence for a causual relationship between flowering and floods or earthquakes does not exist, bamboo flowering is known to cause increases in rodent populations, which multiply rapidly due to the sudden increase in seed availability. After consuming the bamboo seeds, the rodents turn to other sources of grain, such as stored cereals or crop still standing in fields, and thereby cause famines. Rodents are prolific breeders and attain sexual maturity when they are 3½ months old. A litter normally contains about 12-18 babies and a single parent can have upto 4 litters every year. The first three litters would have also begun breeding by the end of the year. The Mizoram Government infact pays Rs. 2.00 for every rat tail delivered to them.

The bamboo in the Anamalais belong to a singular variety, Bambusa bambos, a fast growing species reaching a height of over 100' and a thickness of 7". They are thick-walled but soft, the lower branches being long, wiry and armed with thorns. The inner shoot is edible.

THEORIES

Three major theories to explain mass bamboo flowering at long many-year intervals have been proposed.

  1. The predator satiation hypothesis suggested by Janzen suggests that mass seeding is a means of ensuring some at least seeds survive predators. Many animals eat bamboo seeds, particularly rodents, but also wild fowl and pigs, elephants and other birds. Flowering and seed set encourages predator populations to increase, either by increased fecundity or by migration. This may be fatal to the bamboo seeds if only a limited number of seeds were produced, as none would survive, so the bamboo swamps predators with too many seeds to ensure some survive.
  2. The plant competition theory suggests that under ideal circumstances bamboos maintain dominance over other vegetation in the areas in which they grow (see some of the extensive tracts of forests in India and China for excellent examples) and so to maintain that dominance, mass seeding carpets the ground with offspring and prevents other species from getting a foothold.
  3. The fire cycle hypothesis, put forward by Keeley and Bond, that suggests that large scale death of flowered bamboos increases the chances of fire and the fire removes from competiton any other plants. 

No one theory has found general favour amongst ecologists and foresters, and whatever the original reason, mass flowering at many year intervals remains one of the least understood aspects of the bamboo life cycle.