The annual yield of a bamboo clump depends on the number of new culms produced each year. This in turn is related to the production of young leaves.
Culms become mature after two or three years.
Prior to this stage, young culms contribute greatly to the health of the clump through photosynthesis in their new leaves. The foods they synthesize are partly consumed by leaves but the greater proportion is transported to the rhizomes. Here it is stored as energy which is converted into next year's growth of new shoots. This is why to maximise shoot output some shoots must be left each year to develop into leafy young culms. Clearly it is a marketing advantage to have a number of plantations producing in sequence.