At first sight the giant panda is a paradox. Classified as carnivores it persists in acting like herbivores, feeding almost exclusively on plant material. It has been described as an 'obligate grazer' on bamboo, meaning that it is obliged to eat bamboo and cannot survive without it. More than 99 per cent of the food the giant panda consumes consists of bamboo.
- One of the Most Special Features of the Bamboos – Synchronous Flowering
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When bamboo flowers and dies, nutrients locked up in the plants are released and light can penetrate to the forest floor. This allows tree seedlings a chance to establish and grow |
Along with almost all other bamboos, the species at Wolong have another unusual feature that differentiates them from other members of the grass family - synchronous flowering. During most years the bamboo reproduces itself vegetatively, producing underground runners that send up new shoots to the surface at irregular intervals. This method has served the bamboo very well but by itself it is, in evolutionary terms, a dead end. To ensure long-term viability, sexual reproduction must take place at some point in the bamboo's lifetime so that different combinations of hereditary factors can occur. This ensures the genetic variety that allows a species to adapt to new conditions and new environments. All the grass family reproduces sexually, flowering and setting seed. But it is the bamboo's timetable that sets it apart from the rest of its kind.
Most 'normal' grasses flower every year, and the same is true for a minority of bamboo species. Bamboos such as Arundinaria wightiana, Arundinaria glomerulata, Bambusa lineata and Shibataea kumasasa have never been observed flowering or seeding at greater than yearly intervals. These so-called iteroparous bamboos all grow to maturity and then flower, seed and die on an annual basis. But most bamboo species 'hold back' their flowering cycles for relatively long periods of time. At regular intervals, varying with the species between thirty and 120 years, all the plants flower at the same time and then die. Distance does not seem to affect synchrony: in the late sixties the mainland Chinese giant timber bamboo, Phyllostachys bambusoides, seeded en
Bamboo flowers masse in its homeland; transplanted bamboo of the same species also flowered at this time in Japan, Russia, England and the United States. The cues that trigger such synchronous displays are not well understood.
In Wolong the umbrella bamboo flowers every seventy to eighty years, with the arrow bamboo having a shorter period of between forty-two and forty-eight years.
Appendix: Why do the plants have synchronous flowering?
After the synchronous flowering of the bamboo, the amount of seed produced can be prodigious. The seeds range from the size of a rice kernel to as much as 350 g. During mass seeding, the kernels can lie to a depth of up to 15 cm below the parent plant. A 33m-sq clump of Dendrocalamus strictus produced around 145 kg of seed. At 900 seeds to the ounce, this means that more than four and a half million seeds were set from this small clump of bamboo. Many birds and mammals take advantage of this bounty, everything from rats, mice and porcupines, through pheasants, doves and parrotbills, to Man. Where only a small 'island' of bamboo flowers synchronously the whole crop may be consumed and the species made locally extinct. More usually, however, the hordes of seed-eaters cannot cope with the superabundance of seeds.
Any bamboo in a given area that fails to flower at the 'correct' time will face severe retribution. Those few plants that flower too early will have their seed destroyed because it has not been produced in sufficient numbers to satisfy predators. Similarly, late-flowering plants will fall victim to seed-eating species that have been drawn to the earlier, heavier fall of seed, the survivors of which will, by now, have germinated and no longer be regarded as food by the seed-eaters. The very creatures that feed on the bamboo's seeds are responsible for maintaining synchronous flowering; the cycle is self-policing, once established.
The only species that could defeat this defensive stratagem, as it has defeated so many others, is Man. Humans counteract the mechanism that regulates synchronous flowering because they do not consume either the early- or the late-flowering plants. It is the main block of synchronously seeding plants that are preyed on. Fortunately for the bamboo, human seed collection is confined to a few scattered areas and does not seem to have a serious impact on the ability of the plant to flower in unison. Humans have probably harvested bamboo seed-fall for thousands of )rears, and in periods of famine the plant can substantially affect the chances of human survival. Dendrocalamus seeds were responsible for saving an estimated 35 000 people from starvation during a drought in the central provinces of India between 1899 and 1900. Similarly, the Sasa bamboo of Japan was harvested in times of famine.
In a naturally wild habitat, untouched by Man, the giant panda can usually count on at least one other species of bamboo being available as a dietary fall-back. This species may not be as palatable or even as nutritious as the panda’s favourable bamboo, but it can sustain the animal during the ten to fifteen years that it takes for the panda’s preferred food plant to re-establish itself. Unfortunately, such habitat is becoming increasingly rare nowadays.
