So, is bamboo "green"? Yes. And no. (As you all know by now, I'm a big one for being grey in my green.)
Here are some pluses on bamboo: rapidly renewable for sure. A raw material that provides new stock every five years is pretty hard to beat. (Bamboo should be harvested between ages three to six to get the best-quality material.) It usually grows well without heavy chemical or fertilizer requirements (although there are reports that some new plantations are using them), does not require a lot of maintenance (such as thinning) and generally, if harvested properly, it naturally (even aggressively) regenerates. Harvesting usually does not require a lot of heavy power equipment or secondary forest damage. Finally, it can grow in areas where other woods don't, or can be grown in an economical manner.
Bamboo, like wood, is a great carbon sink…some research suggests that because of its rapid growth rate that it is an even better carbon sink then hardwood. A World Wildlife Fund report estimated that an acre of bamboo can store 6.88 metric tons of carbon annually-about 70 percent more than an acre of hardwoods.
But of course there are negatives as well. Bamboo requires a lot of power and the use of other resources to process. The fibers go through a bleaching process and chemical treatment against insects, and while neither treatment has any potential to cause any health risks to consumers, they do utilize more resources and power. More power is also consumed in the cases where the bamboo is turned caramel-brown in color through a high temperature carbonization process. Much has also been made of the amount of glue required. Most all companies use low-formaldehyde glues, and some bamboo flooring comes formaldehyde-free, but simply because a lot of glue is used, no matter what kind, the processing of bamboo is energy-intensive.
(By the way, "strand" bamboo has the same basic pluses and minuses. Strand uses bamboo fiber that would be otherwise thrown away or burned, so that makes it more green in more fully utilizing the resource and creating a good home for post-industrial waste. However, yes, it uses more glue and energy to create.)
There is also a surprising potential negative that comes from the structure of bamboo. Bamboo has "knuckles" between the segments of its hollow, tube-like stalk. They seal each compartment (which is one reason why bamboo is so strong and why it's been used as a water or food storage device in many regions.) However, when the bamboo is harvested, water often pools in the lower knuckle, and this little stagnant pool has become a breeding ground for mosquitoes. To kill the mosquitoes, some areas have turned to chemical control.
Some people talk about the carbon costs of transporting the bamboo from Asia into the U.S., but container shipping has the lowest carbon footprint of any transportation method. A shipment of bamboo flooring from Asia to Los Angeles is more "green" from the transportation viewpoint than a shipment of red oak trucked over from the East Coast. Location and shipping costs (be they financial or "carbon") will factor into any "green calculation," so I don't see that as a fair consideration to throw only at bamboo.
So bamboo has pluses and negatives; this is no surprise. I think the pluses can outweigh the negatives, and with some common sense and care in harvesting and processing, bamboo can be a very green product. Bamboo is durable and beautiful. Being beautiful doesn't make it green, but the durable aspect will. Properly manufactured bamboo (and hardwood) flooring has a usable "life" of over 25 years, easily beating alternatives like carpet and rubber. Long-term usage of a product is extremely green.
Finally, we have to recognize that bamboo is economically and very socially important. A great deal of Asian culture is interwoven with bamboo. There are many different species, and some feed pandas (not the type used for flooring), some feed humans, some provide scaffolding or other construction material. Where I lived in Japan, the train gates (the poles that came down to block the road when a train passed) were made of brightly painted bamboo stalks. One report I read noted that approximately 6 million people in China alone work in bamboo industries (construction, food, furniture, farming, etc.) and over 600 million people worldwide rely on income from some species or use of bamboo. In my mind, this is a factor in "green" as well, recognizing the extended benefits provided to a huge number of people.
And there is no reason Americans can't enjoy the benefit and beauty of bamboo, as well.