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Bamboo
by Susan Lumpkin

Giant and red pandas depend on bamboo for survival. So do billions of people in Asia, where bamboo forms an extraordinarily important part of everyday life. Bamboo shoots and seeds provide food for people, stems and leaves provide forage for live-stock. People fashion bamboo into hats, baskets, tools, toys, musical instruments, furniture, chopsticks, paper, and weapons. A secretion of some bamboos, called tabsheer, is traditionally prescribed for coughs and asthma; it is also used as an aphrodisiac.

Bamboo stems are used to build houses, to make the tables and chairs that furnish the houses, and the fences that surround them. Workers scale bamboo scaffolding to construct even the tallest buildings in Asia. These flimsy-looking structures are actually models of resilience, merely swaying in typhoons that collapse steel frameworks. A bridge over the Min River in Sichuan hangs from cables of twisted bamboo—and has done so for more than 1,000 years!

In botanical circles, debates rage over the bamboos. Even the seemingly simple question of how many species there are yields answers varying from more than 200 to 1,200. And no one can quite agree on what to call each of these species, however many there might be. In fact, bamboos, members of the grass family, are amazingly diverse and widespread plants. What distinguishes bamboos from other grasses - and makes them so useful - are their woody culms, or stalks. Some bamboo giants reach heights of 60 to 90 feet, with culms up to eight inches or more in diameter. Others are delicate dwarfs, still others are all sizes in between. Most bamboos live in subtropical or tropical habitats, but some, like those of western China that giant pandas feed on, have adapted to cooler climates in areas of high rainfall and humidity. Canebreaks, once very common in the south eastern United States, are native North American bamboos, but the bamboos grown in gardens all over the Washington area are species introduced from China and Japan.

Many bamboos also share the habit of "gregarious flowering": All members of a particular species flower, produce seeds, then die in synchrony throughout their distribution. And they do this at intervals that range, depending on the species, from three to 120 years. How bamboos "know" when to flower remains a mystery, but scientists suspect that a genetically programmed "clock," rather than environmental factors, controls gregarious flowering.

Why bamboos flower and die gregariously has more to do with seeds than flowers. When bamboos finally get around to it, they set massive crops of seeds. A 40-square-yard clump of one Indian species may produce more than 300 pounds of seeds—at between 800 and 1,000 seeds per ounce! One oft-told tale is of a surveyor who had to quit working when the pear-sized seeds of another Indian bamboo were falling so thickly, over a 6,000-square-mile area, that they were breaking his instruments. Having put prodigious amounts of energy into seeds, the bamboos are spent, and die.

Massive seeding in synchrony may have evolved in response to the multitudes of seed predators, from rats and birds to rhinos and elephants and people, that find bamboo seeds appealing. A bamboo producing only a few seeds at a time risks having all of those seeds eaten. But huge seed crops swamp predators—they simply can’t eat them all—so many seeds survive to grow into plants. And a bamboo that produces seeds when all the other bamboos are producing seeds will see more of its seeds survive than a bamboo that drops seeds alone.

Between flowerings, bamboos reproduce vegetatively via rhizomes. The rhizomes develop underground and, once a year, the bamboo sends up shoots that emerge from sheaths to grow into culms. In many species these shoots grow incredibly fast - the record is a Japanese bamboo culm that grew almost four feet in a day! In contrast, bamboos grown from seed may take five to 20 years to reach full size and maturity. So for all who depend on bamboo—giant pandas, red pandas, and people—flowering predicts privation for years to come.

(ZooGoer 21(2) 1992. Copyright 1992 Friends of the National Zoo. All rights reserved.)

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